Chapter 47: SystemUI

SystemUI is the Android process responsible for nearly everything visible on screen outside of the currently focused application. It draws the status bar, the notification shade, Quick Settings, the lock screen, the navigation bar, the volume dialog, the power menu, the screenshot experience, and the recent-apps overlay. It lives in a single APK that runs as a persistent system service under the UID android.uid.systemui and cannot be killed without the framework automatically restarting it through RescueParty.

SystemUI is one of the largest single packages in AOSP. Its source directory contains over 187 sub-packages under src/com/android/systemui/, covering domains from accessibility to wmshell. The codebase is undergoing a multi-year migration: legacy single-class god-objects are being replaced by an MVI architecture (Model-View-Intent) with Dagger dependency injection, Kotlin coroutines, and Jetpack Compose.

This chapter examines every major subsystem in detail, tracing the code from process startup through each visible surface.

---

47.1 SystemUI Architecture

47.1.1 Process Startup

SystemUI is declared in its manifest with android:sharedUserId="android.uid.systemui" and coreApp="true":

<!-- frameworks/base/packages/SystemUI/AndroidManifest.xml -->
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.android.systemui"
    android:sharedUserId="android.uid.systemui"
    coreApp="true">

The process starts when system_server calls IStatusBarService.registerStatusBar(). The entry point is SystemUIService, a plain Android Service:

// frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIService.java
public class SystemUIService extends Service {
    @Inject
    public SystemUIService(
            @Main Handler mainHandler,
            DumpHandler dumpHandler,
            BroadcastDispatcher broadcastDispatcher,
            LogBufferEulogizer logBufferEulogizer,
            LogBufferFreezer logBufferFreezer,
            BatteryStateNotifier batteryStateNotifier,
            UncaughtExceptionPreHandlerManager uncaughtExceptionPreHandlerManager) {
        // ...
    }

    @Override
    public void onCreate() {
        super.onCreate();
        // Start all of SystemUI
        ((SystemUIApplication) getApplication()).startSystemUserServicesIfNeeded();
        // ...
    }
}

The Application subclass is SystemUIApplicationImpl. Its onCreate initialises the Dagger graph and registers for BOOT_COMPLETED:

// frameworks/base/packages/SystemUI/src/com/android/systemui/application/impl/
//   SystemUIApplicationImpl.java
public class SystemUIApplicationImpl extends SystemUIApplication
        implements ApplicationContextInitializer, HasWMComponent {

    @Override
    public void onCreate() {
        super.onCreate();
        TimingsTraceLog log = new TimingsTraceLog("SystemUIBootTiming",
                Trace.TRACE_TAG_APP);
        log.traceBegin("DependencyInjection");
        mInitializer = mContextAvailableCallback.onContextAvailable(this);
        mSysUIComponent = mInitializer.getSysUIComponent();
        mBootCompleteCache = mSysUIComponent.provideBootCacheImpl();
        log.traceEnd();
        // ...
    }
}

47.1.2 Dagger Dependency Injection

SystemUI uses a three-level Dagger component hierarchy:

graph TD
    A["GlobalRootComponent<br/>(process-scoped)"] --> B["SysUIComponent<br/>(@SysUISingleton)"]
    A --> C["WMComponent<br/>(Window Manager Shell)"]
    B --> D["KeyguardBouncerComponent"]
    B --> E["DozeComponent"]
    B --> F["ComplicationComponent"]
    B --> G["HomeStatusBarComponent"]
    B --> H["SystemUIDisplaySubcomponent"]

GlobalRootComponent is the top-level component. It is bound to the Context of the application and exposes the SysUIComponent.Builder:

// frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/
//   GlobalRootComponent.java
public interface GlobalRootComponent {
    interface Builder {
        @BindsInstance Builder context(Context context);
        @BindsInstance Builder instrumentationTest(@InstrumentationTest boolean test);
        GlobalRootComponent build();
    }

    WMComponent.Builder getWMComponentBuilder();
    SysUIComponent.Builder getSysUIComponent();
    InitializationChecker getInitializationChecker();
    @Main Looper getMainLooper();
}

SysUIComponent is the main subcomponent where most of SystemUI's singletons live. It installs a large number of Dagger modules:

// frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/
//   SysUIComponent.java
@SysUISingleton
@Subcomponent(modules = {
        DefaultComponentBinder.class,
        DependencyProvider.class,
        MultiUserUtilsModule.class,
        NotificationInsetsModule.class,
        QsFrameTranslateModule.class,
        ReferenceSystemUIModule.class,
        StartControlsStartableModule.class,
        StartBinderLoggerModule.class,
        SystemUIModule.class,
        SystemUICoreStartableModule.class,
        WallpaperModule.class})
public interface SysUIComponent {
    // ...
    Map<Class<?>, Provider<CoreStartable>> getStartables();
    @PerUser Map<Class<?>, Provider<CoreStartable>> getPerUserStartables();
}

The builder accepts shell interfaces from WMComponent, such as Pip, SplitScreen, Bubbles, and ShellTransitions. This is how SystemUI integrates with the window manager shell process.

SystemUIInitializer orchestrates the Dagger graph construction:

// frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIInitializer.java
public abstract class SystemUIInitializer {
    public void init(boolean fromTest) throws ExecutionException, InterruptedException {
        mRootComponent = getGlobalRootComponentBuilder()
                .context(mContext)
                .instrumentationTest(fromTest)
                .build();

        // Stand up WMComponent
        setupWmComponent(mContext);

        // Build SysUI, injecting Shell interfaces
        SysUIComponent.Builder builder = mRootComponent.getSysUIComponent();
        builder = prepareSysUIComponentBuilder(builder, mWMComponent)
                .setShell(mWMComponent.getShell())
                .setPip(mWMComponent.getPip())
                .setSplitScreen(mWMComponent.getSplitScreen())
                // ... more shell bindings
                ;
        mSysUIComponent = builder.build();

        Dependency dependency = mSysUIComponent.createDependency();
        dependency.start();
    }
}

47.1.3 CoreStartable -- The Service Lifecycle

Every major SystemUI feature is implemented as a CoreStartable. This interface defines the lifecycle that the application drives:

CoreStartable
  +-- start()          // Called once, in topological order
  +-- onBootCompleted()
  +-- isDumpCritical() // Included in bugreport CRITICAL section?
  +-- dump()           // For `adb shell dumpsys`

CoreStartables are registered in Dagger modules using multibinding:

// frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/
//   SystemUICoreStartableModule.kt
@Module
abstract class SystemUICoreStartableModule {
    @Binds @IntoMap @ClassKey(KeyguardViewMediator::class)
    abstract fun bindKeyguardViewMediator(sysui: KeyguardViewMediator): CoreStartable

    @Binds @IntoMap @ClassKey(GlobalActionsComponent::class)
    abstract fun bindGlobalActionsComponent(sysui: GlobalActionsComponent): CoreStartable

    @Binds @IntoMap @ClassKey(WMShell::class)
    abstract fun bindWMShell(sysui: WMShell): CoreStartable

    // ... 30+ more bindings
}

The application starts them with a topological sort that respects declared dependencies:

// SystemUIApplicationImpl.java -- topological start loop
boolean startedAny = false;
ArrayDeque<Map.Entry<Class<?>, Provider<CoreStartable>>> queue;
ArrayDeque<Map.Entry<Class<?>, Provider<CoreStartable>>> nextQueue =
        new ArrayDeque<>(startables.entrySet());

do {
    startedAny = false;
    queue = nextQueue;
    nextQueue = new ArrayDeque<>(startables.size());
    while (!queue.isEmpty()) {
        Map.Entry<Class<?>, Provider<CoreStartable>> entry = queue.removeFirst();
        Class<?> cls = entry.getKey();
        Set<Class<? extends CoreStartable>> deps =
                mSysUIComponent.getStartableDependencies().get(cls);
        if (deps == null || startedStartables.containsAll(deps)) {
            mServices[i] = startStartable(clsName, entry.getValue());
            startedStartables.add(cls);
            startedAny = true;
        } else {
            nextQueue.add(entry);
        }
    }
} while (startedAny && !nextQueue.isEmpty());

If any startable's dependencies cannot be resolved, the process throws a RuntimeException with details about which dependencies are missing.

47.1.4 Plugin System

SystemUI supports runtime extensibility through a plugin architecture. Plugins are APKs that implement interfaces from the plugin source set:

frameworks/base/packages/SystemUI/plugin/src/com/android/systemui/plugins/
  qs/QSTile.java
  qs/QSFactory.java
  qs/QS.java
  GlobalActions.java
  VolumeDialogController.java
  ...

The ExtensionController discovers and loads plugins, with the GlobalActionsComponent being a canonical example:

// frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/
//   GlobalActionsComponent.java
@Override
public void start() {
    mExtension = mExtensionController.newExtension(GlobalActions.class)
            .withPlugin(GlobalActions.class)
            .withDefault(mGlobalActionsProvider::get)
            .withCallback(this::onExtensionCallback)
            .build();
    mPlugin = mExtension.get();
}

This pattern allows OEMs to replace the default power menu, volume dialog, or QS tiles by shipping a plugin APK signed with the platform key.

47.1.5 Feature Flags

SystemUI uses Android's aconfig flag system for feature gating. Flags are defined in:

frameworks/base/packages/SystemUI/aconfig/

Code checks flags via generated accessors:

import com.android.systemui.Flags;

if (Flags.predictiveBackAnimateShade()) {
    // new behavior
}

The QS pipeline has its own flag repository:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/pipeline/shared/
//   QSPipelineFlagsRepository.kt
@SysUISingleton
class QSPipelineFlagsRepository @Inject constructor() {
    val tilesEnabled: Boolean
        get() = AconfigFlags.qsNewTiles()
}

47.1.6 Directory Structure

The following is an abbreviated listing of the 187+ sub-packages under src/com/android/systemui/:

accessibility/    -- Magnification, floating menu
activity/         -- Activity lifecycle helpers
ambient/          -- Ambient display
authentication/   -- Device authentication domain layer
back/             -- Predictive back gesture
battery/          -- Battery state
biometrics/       -- Fingerprint, face, UDFPS
bluetooth/        -- Bluetooth QS tile data
bouncer/          -- Keyguard bouncer (MVI)
brightness/       -- Brightness slider
camera/           -- Camera access tracking
charging/         -- Charging animation
classifier/       -- Touch classifier (falsing)
clipboardoverlay/ -- Clipboard preview overlay
communal/         -- Communal (glanceable hub) mode
controls/         -- Device controls (home automation)
dagger/           -- DI components and modules
demomode/         -- Demo mode for screenshots
display/          -- Display management
doze/             -- Doze/AOD
dreams/           -- Screen saver (daydream)
flags/            -- Feature flag infrastructure
fragments/        -- Fragment host
globalactions/    -- Power menu
keyguard/         -- Lock screen
media/            -- Media controls, route picker
navigationbar/    -- Navigation bar and gesture nav
notifications/    -- Notification pipeline
plugins/          -- Plugin infrastructure
power/            -- Power domain layer
privacy/          -- Privacy indicators
qs/               -- Quick Settings
recents/          -- Recent apps
scene/            -- Scene container (next-gen UI)
screenshot/       -- Screenshot capture and editing
shade/            -- Notification shade
statusbar/        -- Status bar, icons, policies
volume/           -- Volume dialog
wallpapers/       -- Wallpaper management
wmshell/          -- WM Shell integration

graph LR
    subgraph "SystemUI Process"
        SysUIApp["SystemUIApplicationImpl"]
        SysUIApp --> DI["Dagger Graph"]
        DI --> CS["CoreStartable Map"]
        CS --> SB["CentralSurfacesImpl"]
        CS --> KVM["KeyguardViewMediator"]
        CS --> GAC["GlobalActionsComponent"]
        CS --> WMS["WMShell"]
        CS --> VOL["VolumeUI"]
        CS --> CLIP["ClipboardListener"]
        CS --> MAG["Magnification"]
        CS --> MORE["30+ more..."]
    end

---

47.2 Status Bar

The status bar is the narrow strip at the top of the screen that displays the clock, notification icons, battery level, signal strength, and system status icons. It is one of the first visual elements created during SystemUI startup.

47.2.1 CentralSurfaces -- The Orchestrator

CentralSurfaces is an interface extending both CoreStartable and LifecycleOwner. Its implementation, CentralSurfacesImpl, is a 3,291-line class that historically served as the central coordinator for the status bar, notification shade, keyguard, and more:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/
//   CentralSurfaces.java
public interface CentralSurfaces extends Dumpable, LifecycleOwner, CoreStartable {
    String TAG = "CentralSurfaces";
    boolean SHOW_LOCKSCREEN_MEDIA_ARTWORK = true;
    long LAUNCH_TRANSITION_TIMEOUT_MS = 5000;
    // ...
}

CentralSurfacesImpl is injected with an enormous constructor -- it depends on virtually every other SystemUI component. It manages:

• Status bar window creation and positioning
• Notification shade expansion
• Keyguard/bouncer transitions
• Light bar (dark/light icon tinting)
• Biometric unlock animations
• Media artwork on lock screen
• Demo mode

The class is progressively being decomposed. New code should depend on narrower interfaces (e.g., ShadeController, ShadeViewController, KeyguardStateController) rather than CentralSurfaces directly.

47.2.2 StatusBarWindowController

The status bar occupies a system window of type WindowManager.LayoutParams.TYPE_STATUS_BAR. Its window management is encapsulated in StatusBarWindowControllerImpl:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/window/
//   StatusBarWindowControllerImpl.java
public class StatusBarWindowControllerImpl implements StatusBarWindowController {
    // Window type, insets configuration, cutout handling
}

Key aspects of the status bar window:

Property	Value
Window type	TYPE_STATUS_BAR
Pixel format	PixelFormat.TRANSLUCENT
Cutout mode	LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS
Gravity	Gravity.TOP
Flags	FLAG_NOT_FOCUSABLE, FLAG_TOUCHABLE_WHEN_WAKING

The controller handles display cutouts (notches, punch-holes) and configures InsetsFrameProvider so that the status bar participates in the inset system. Applications receive statusBars() insets corresponding to the height of this window.

47.2.3 CollapsedStatusBarFragment

The visible content of the status bar is managed by CollapsedStatusBarFragment, a Fragment that inflates the R.layout.status_bar layout:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/
//   fragment/CollapsedStatusBarFragment.java
public class CollapsedStatusBarFragment extends Fragment
        implements CommandQueue.Callbacks,
                   StatusBarStateController.StateListener,
                   SystemStatusAnimationCallback {
    // Manages icon visibility, system event animations, ongoing call chip
}

The fragment listens to several signals:

• CommandQueue.Callbacks -- disable flags from system_server that hide icons
• StatusBarStateController -- state transitions (SHADE, KEYGUARD, SHADE_LOCKED)
• SystemStatusAnimationCallback -- animated chips for privacy indicators
• ShadeExpansionStateManager -- fading out icons during shade expansion

47.2.4 PhoneStatusBarView

PhoneStatusBarView is the root View of the collapsed status bar:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/
//   PhoneStatusBarView.java
public class PhoneStatusBarView extends BaseStatusBarFrameLayout
        implements DarkReceiverImpl.DarkReceiver {
    // Touch handling, dark mode tinting
}

The view controller (PhoneStatusBarViewController) coordinates dark/light icon tinting based on the underlying content, using region sampling to determine whether the wallpaper or app content below the status bar is light or dark.

47.2.5 Status Bar Icon Pipeline

Icons in the status bar flow through a multi-stage pipeline:

graph LR
    A["StatusBarManager<br/>setIcon()"] --> B["CommandQueue"]
    B --> C["StatusBarIconController"]
    C --> D["DarkIconManager"]
    D --> E["StatusBarIconView"]
    E --> F["NotificationIconContainer"]

The StatusBarIconController maintains the list of icons and their visibility. DarkIconManager applies tinting: white icons over dark backgrounds, dark icons over light backgrounds. The tinting boundary is computed by LightBarController using the Drawable content of the window behind the status bar.

47.2.6 Status Bar States

The status bar operates in several logical states managed by StatusBarStateControllerImpl:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/
//   StatusBarState.java
public class StatusBarState {
    public static final int SHADE = 0;          // Normal unlocked
    public static final int KEYGUARD = 1;       // Lock screen
    public static final int SHADE_LOCKED = 2;   // Shade pulled down over keyguard
}

Transitions between states drive animations throughout SystemUI. The state controller broadcasts changes to all registered StateListener instances.

stateDiagram-v2
    [*] --> SHADE : Device unlocked
    [*] --> KEYGUARD : Device locked
    KEYGUARD --> SHADE_LOCKED : Pull down shade
    SHADE_LOCKED --> KEYGUARD : Collapse shade
    KEYGUARD --> SHADE : Unlock
    SHADE --> KEYGUARD : Lock

---

47.3 Notification Shade

The notification shade is the panel that slides down from the top of the screen, revealing notifications and Quick Settings. It is one of the most complex UI components in Android.

47.3.1 Window Configuration

The notification shade occupies a separate window from the status bar. Its window type is TYPE_NOTIFICATION_SHADE (a special type that allows it to receive input above other system windows):

// frameworks/base/packages/SystemUI/src/com/android/systemui/shade/
//   NotificationShadeWindowControllerImpl.java
@SysUISingleton
public class NotificationShadeWindowControllerImpl
        implements NotificationShadeWindowController, Dumpable {
    // Manages the notification shade window parameters
    // Adjusts focus, touchability, and dimensions based on state
}

The window controller dynamically adjusts the window parameters based on the current state:

State	Window Behaviour
Shade collapsed	Not focusable, minimal height
Shade expanding	Expanding height, receives touch
Shade expanded	Full screen, focusable for remote input
Keyguard	Full screen, bouncer may be focusable
Dozing/AOD	Minimal, low power

47.3.2 NotificationPanelViewController

At 4,329 lines, NotificationPanelViewController is the primary controller for the shade panel. It manages:

• Touch tracking and velocity-based expansion/collapse
• QS expansion within the shade
• Keyguard-specific behaviour (clock, notifications on lock screen)
• Split shade on large screens (notifications left, QS right)
• Blur effects during expansion

// frameworks/base/packages/SystemUI/src/com/android/systemui/shade/
//   NotificationPanelViewController.java
public class NotificationPanelViewController
        implements Dumpable, ShadeViewController, ShadeSurface {
    // Handles all shade panel touch events and state transitions
}

Key touch handling flow:

sequenceDiagram
    participant User
    participant NSWV as NotificationShadeWindowView
    participant NPVC as NotificationPanelViewController
    participant FC as FalsingCollector
    participant SC as ShadeController

    User->>NSWV: ACTION_DOWN on status bar
    NSWV->>NPVC: onTouchEvent()
    NPVC->>FC: onTouchEvent() (classify gesture)
    NPVC->>NPVC: Track expansion fraction
    User->>NSWV: ACTION_MOVE (drag down)
    NSWV->>NPVC: onTouchEvent()
    NPVC->>NPVC: Update expansion (0.0 → 1.0)
    User->>NSWV: ACTION_UP
    NSWV->>NPVC: onTouchEvent()
    NPVC->>NPVC: Calculate fling velocity
    alt Velocity > threshold
        NPVC->>SC: animateExpandShade()
    else Velocity < threshold
        NPVC->>SC: animateCollapseShade()
    end

47.3.3 ShadeController

ShadeController is the interface that abstracts shade operations. It extends CoreStartable:

// frameworks/base/packages/SystemUI/src/com/android/systemui/shade/
//   ShadeController.java
public interface ShadeController extends CoreStartable {
    boolean isShadeEnabled();
    void instantExpandShade();
    void instantCollapseShade();
    void animateCollapseShade(int flags, boolean force,
                              boolean delayed, float speedUpFactor);
    void animateExpandShade();
    void animateExpandQs();
    void cancelExpansionAndCollapseShade();
    boolean isShadeFullyOpen();
    boolean isExpandingOrCollapsing();
    void collapseShade();
    void collapseShadeForActivityStart();
    // ...
}

The default implementation is ShadeControllerImpl, while ShadeControllerSceneImpl is the next-generation implementation for the scene container architecture.

47.3.4 NotificationStackScrollLayout

The notification list is rendered by NotificationStackScrollLayout, a custom ViewGroup that implements:

• Variable-height child views (notification rows)
• Over-scroll physics
• Dismissal gestures (swipe to dismiss)
• Grouping and section headers
• Heads-up notification insertion
• Shelf for overflow icons

Each notification row is an ExpandableNotificationRow, which itself contains inflated notification views (contracted, expanded, heads-up variants).

47.3.5 Scrim Management

The scrim (dimming overlay) behind the shade is managed by ScrimController, which handles multiple scrim layers:

graph TD
    A["ScrimController"] --> B["ScrimBehind<br/>(behind shade)"]
    A --> C["ScrimInFront<br/>(above shade, for bouncer)"]
    A --> D["NotificationsScrim<br/>(behind notifications)"]
    A --> E["ScrimState Machine"]
    E --> F["UNINITIALIZED"]
    E --> G["KEYGUARD"]
    E --> H["SHADE_LOCKED"]
    E --> I["BOUNCER"]
    E --> J["UNLOCKED"]
    E --> K["PULSING"]

Each ScrimState defines alpha values and tint colours for the scrims. Transitions between states animate these properties smoothly.

47.3.6 Lockscreen-to-Shade Transition

The LockscreenShadeTransitionController manages the drag-down gesture from the lock screen into the shade. It coordinates:

• QS expansion fraction
• Scrim alpha transitions
• Keyguard visibility
• Notification position interpolation

---

47.4 Quick Settings

Quick Settings (QS) is the tile grid accessible by pulling down the notification shade. The first pull shows a "Quick QS" strip of a few tiles; a second pull expands to the full QS panel.

47.4.1 Architecture Overview

graph TD
    subgraph "Quick Settings"
        QSHost["QSHost<br/>(tile management)"]
        QSPanel["QSPanel<br/>(full tile grid)"]
        QuickQS["QuickQSPanel<br/>(collapsed strip)"]
        QSTileImpl["QSTileImpl<br/>(base tile class)"]
        CustomTile["CustomTile<br/>(third-party tiles)"]
    end
    QSHost --> QSTileImpl
    QSHost --> CustomTile
    QSTileImpl --> QSPanel
    QSTileImpl --> QuickQS

47.4.2 QSHost -- Tile Management

QSHost is the interface that manages the set of active QS tiles:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/QSHost.java
public interface QSHost {
    String TILES_SETTING = Settings.Secure.QS_TILES;

    static List<String> getDefaultSpecs(Resources res) {
        final ArrayList<String> tiles = new ArrayList();
        int resource = QsInCompose.isEnabled()
                ? R.string.quick_settings_tiles_new_default
                : R.string.quick_settings_tiles_default;
        final String defaultTileList = res.getString(resource);
        tiles.addAll(Arrays.asList(defaultTileList.split(",")));
        return tiles;
    }

    Collection<QSTile> getTiles();
    void addTile(String spec);
    void addTile(String spec, int requestPosition);
    void addTile(ComponentName tile);
    void removeTile(String tileSpec);
    QSTile createTile(String tileSpec);
    void changeTilesByUser(List<String> previousTiles, List<String> newTiles);
}

The tile configuration is stored in Settings.Secure.QS_TILES as a comma-separated list of tile specs (e.g., "wifi,bt,flashlight,rotation"). The default set is defined in a string resource, which OEMs commonly overlay.

47.4.3 QSTile Interface

Every QS tile implements the QSTile plugin interface:

// frameworks/base/packages/SystemUI/plugin/src/com/android/systemui/plugins/qs/
//   QSTile.java
@ProvidesInterface(version = QSTile.VERSION)
public interface QSTile {
    int VERSION = 5;

    String getTileSpec();
    boolean isAvailable();
    void refreshState();
    void click(@Nullable Expandable expandable);
    void secondaryClick(@Nullable Expandable expandable);
    void longClick(@Nullable Expandable expandable);
    @NonNull State getState();
    CharSequence getTileLabel();
    void setListening(Object client, boolean listening);
    void destroy();
}

The State inner class carries all visual state:

Field	Description
state	Tile.STATE_ACTIVE, STATE_INACTIVE, STATE_UNAVAILABLE
icon	Drawable or resource
label	Primary text
secondaryLabel	Secondary text (e.g., network name)
contentDescription	Accessibility
dualTarget	Whether long press has a separate action

47.4.4 QSTileImpl -- Base Implementation

QSTileImpl is the abstract base class for built-in tiles:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tileimpl/
//   QSTileImpl.java
public abstract class QSTileImpl<TState extends State>
        implements QSTile, LifecycleOwner, Dumpable {

    protected final QSHost mHost;
    private static final long DEFAULT_STALE_TIMEOUT = 10 * DateUtils.MINUTE_IN_MILLIS;

    // Subclasses must implement:
    // - newTileState()
    // - handleClick()
    // - handleUpdateState(TState state, Object arg)
    // - getLongClickIntent()
    // - getTileLabel()
}

State management runs on a background looper. The flow is:

sequenceDiagram
    participant System as System Event
    participant Tile as QSTileImpl
    participant Handler as Background Handler
    participant View as QSTileView

    System->>Tile: Callback (e.g., WiFi state changed)
    Tile->>Tile: refreshState()
    Tile->>Handler: H.REFRESH_STATE message
    Handler->>Tile: handleRefreshState()
    Tile->>Tile: handleUpdateState(state, arg)
    Tile->>View: handleStateChanged(state)
    View->>View: Update icon, label, colours

47.4.5 Built-in Tiles

AOSP ships approximately 35 built-in QS tiles:

frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tiles/
  AirplaneModeTile.java        LocationTile.java
  AlarmTile.kt                 MicrophoneToggleTile.java
  BatterySaverTile.java        MobileDataTile.kt
  BluetoothTile.java           ModesDndTile.kt
  CameraToggleTile.java        NfcTile.java
  CastTile.java                NightDisplayTile.java
  ColorCorrectionTile.java     NotesTile.kt
  ColorInversionTile.java      OneHandedModeTile.java
  DataSaverTile.java           QRCodeScannerTile.java
  DeviceControlsTile.kt        QuickAccessWalletTile.java
  DreamTile.java               ReduceBrightColorsTile.java
  FlashlightTile.java          RotationLockTile.java
  FontScalingTile.kt           ScreenRecordTile.java
  HearingDevicesTile.java      UiModeNightTile.java
  HotspotTile.java             WifiTile.kt
  InternetTileNewImpl.kt       WorkModeTile.java

Each tile follows the same pattern. Here is FlashlightTile as a representative example:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tiles/
//   FlashlightTile.java
public class FlashlightTile extends QSTileImpl<BooleanState>
        implements FlashlightController.FlashlightListener {

    public static final String TILE_SPEC = "flashlight";
    private final FlashlightController mFlashlightController;

    @Inject
    public FlashlightTile(
            QSHost host,
            QsEventLogger uiEventLogger,
            @Background Looper backgroundLooper,
            @Main Handler mainHandler,
            FalsingManager falsingManager,
            MetricsLogger metricsLogger,
            StatusBarStateController statusBarStateController,
            ActivityStarter activityStarter,
            QSLogger qsLogger,
            FlashlightController flashlightController) {
        super(host, uiEventLogger, backgroundLooper, mainHandler,
                falsingManager, metricsLogger, statusBarStateController,
                activityStarter, qsLogger);
        mFlashlightController = flashlightController;
        mFlashlightController.observe(getLifecycle(), this);
    }
}

Modern tiles like WifiTile use a layered architecture with domain interactors:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tiles/
//   WifiTile.kt
class WifiTile @Inject constructor(
    private val host: QSHost,
    // ...
    private val dataInteractor: WifiTileDataInteractor,
    private val tileMapper: WifiTileMapper,
    private val userActionInteractor: WifiTileUserActionInteractor,
) : QSTileImpl<QSTile.State?>(/* ... */) {
    // Data flows through interactor -> mapper -> view
}

47.4.6 Custom Tiles (Third-Party)

Third-party apps can add QS tiles by implementing android.service.quicksettings.TileService. SystemUI manages these through CustomTile:

// frameworks/base/packages/SystemUI/src/com/android/systemui/qs/external/
//   CustomTile.java
public class CustomTile extends QSTileImpl<State>
        implements TileChangeListener, CustomTileInterface {
    public static final String PREFIX = "custom(";
    // Tile spec format: "custom(com.example.app/.MyTileService)"
}

The lifecycle of a custom tile is managed by TileLifecycleManager, which binds to the third-party TileService and manages the IQSTileService interface. TileServiceManager throttles bindings to prevent resource exhaustion.

graph LR
    subgraph "SystemUI Process"
        CT["CustomTile"]
        TLM["TileLifecycleManager"]
        TSM["TileServiceManager"]
        TS["TileServices"]
    end
    subgraph "App Process"
        TService["TileService"]
    end
    CT --> TLM
    TLM --> TSM
    TSM --> TS
    TLM -.->|bindService| TService
    TService -.->|IQSTileService| TLM

47.4.7 Auto-Add Tiles

Some tiles are automatically added when certain conditions are met (e.g., the Work Profile tile appears when a managed profile is created). This logic is implemented in the QS pipeline's data layer:

frameworks/base/packages/SystemUI/src/com/android/systemui/qs/pipeline/
  data/    -- Repositories for tile data and auto-add rules
  domain/  -- Interactors for tile lifecycle
  shared/  -- Shared flags and models

47.4.8 QSPanel Layout

The full QS panel uses QSPanel with TileLayout (or PagedTileLayout for pagination). The Quick QS strip uses QuickQSPanel with QuickTileLayout. Both are managed by their respective controllers (QSPanelController, QuickQSPanelController).

graph TD
    QSFragment["QSFragmentLegacy / QSFragmentCompose"]
    QSFragment --> QSImpl["QSImpl"]
    QSImpl --> QSContainerImpl["QSContainerImpl"]
    QSContainerImpl --> QuickStatusBarHeader["QuickStatusBarHeader"]
    QSContainerImpl --> QSPanel["QSPanel"]
    QuickStatusBarHeader --> QuickQSPanel["QuickQSPanel"]
    QSPanel --> TileLayout["TileLayout / PagedTileLayout"]
    TileLayout --> TileView1["QSTileView"]
    TileLayout --> TileView2["QSTileView"]
    TileLayout --> TileViewN["..."]

---

47.5 Lock Screen

The lock screen (keyguard) is a critical security surface. It must display before any user content is visible and must correctly manage authentication (PIN, pattern, password, biometrics).

47.5.1 KeyguardViewMediator

KeyguardViewMediator is the largest CoreStartable in SystemUI at 4,573 lines. It mediates between the KeyguardService (which receives lock/unlock commands from the framework) and the keyguard UI:

// frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/
//   KeyguardViewMediator.java
public class KeyguardViewMediator implements CoreStartable, Dumpable {
    // Manages keyguard lifecycle: show, hide, dismiss, lock
}

Key responsibilities:

Responsibility	Description
Lock timeout	Schedules lock after screen-off timeout
Keyguard sounds	Lock/unlock sound effects
SIM PIN handling	Prompts for SIM unlock
Trust agents	Integrates with Smart Lock
Occlusion	Handles activities shown over keyguard
Unlock animation	Coordinates the unlock transition

The mediator receives callbacks from system_server through ViewMediatorCallback:

sequenceDiagram
    participant SS as system_server
    participant KS as KeyguardService
    participant KVM as KeyguardViewMediator
    participant SBKVM as StatusBarKeyguardViewManager
    participant UI as Keyguard UI

    SS->>KS: setShowingLocked(true)
    KS->>KVM: onStartedGoingToSleep()
    KVM->>KVM: doKeyguardLocked()
    KVM->>SBKVM: show(options)
    SBKVM->>UI: Inflate/show bouncer or lockscreen

47.5.2 StatusBarKeyguardViewManager

StatusBarKeyguardViewManager bridges the mediator and the actual keyguard views. It manages the primary bouncer (PIN/pattern/password input), the alternate bouncer (biometric prompt), and the keyguard-to-shade transitions:

// frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/
//   StatusBarKeyguardViewManager.java
@SysUISingleton
public class StatusBarKeyguardViewManager implements Dumpable {
    // Manages bouncer visibility, predictive back animation,
    // alternate bouncer, global actions visibility
}

It interacts with several domain interactors from the new MVI architecture:

• PrimaryBouncerInteractor -- shows/hides the PIN/pattern/password bouncer
• AlternateBouncerInteractor -- manages the biometric (UDFPS) bouncer
• KeyguardDismissActionInteractor -- handles dismiss actions after unlock
• KeyguardTransitionInteractor -- tracks keyguard state transitions

47.5.3 Bouncer

The bouncer is the security challenge (PIN, pattern, or password). Its implementation lives in:

frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/
  data/repository/BouncerRepositoryModule.kt
  domain/interactor/BouncerInteractor.kt
  domain/interactor/PrimaryBouncerInteractor.kt
  domain/interactor/AlternateBouncerInteractor.kt
  domain/startable/BouncerStartable.kt
  ui/BouncerView.kt

The bouncer follows the MVI pattern:

graph LR
    A["BouncerRepository<br/>(data)"] --> B["BouncerInteractor<br/>(domain)"]
    B --> C["BouncerViewModel<br/>(presentation)"]
    C --> D["BouncerView<br/>(UI)"]
    D -->|"User input"| B

47.5.4 AOD (Always-On Display) Integration

When the device is dozing, the lock screen transitions to Always-On Display mode. This is coordinated by:

• DozeServiceHost -- bridges the DreamService-based doze with SystemUI
• DozeScrimController -- manages scrim opacity during doze
• DozeParameters -- configuration (pulse on notification, tap-to-check)

The keyguard state machine includes AOD-specific transitions:

stateDiagram-v2
    [*] --> OFF
    OFF --> AOD : Screen off, doze enabled
    AOD --> LOCKSCREEN : Wake by lift, tap, notification
    LOCKSCREEN --> AOD : Screen off timeout
    LOCKSCREEN --> BOUNCER : Security challenge
    BOUNCER --> GONE : Correct credentials
    AOD --> PULSING : Notification arrives
    PULSING --> AOD : Pulse timeout
    GONE --> OFF : Screen off

47.5.5 Lock Screen Customization

The lock screen supports:

• Clock customization -- pluggable clock faces via ClockRegistryModule
• Quick affordances -- shortcuts on the lock screen corners (camera, wallet)
• Complication -- weather, date, battery on AOD
• Wallpaper -- distinct lock screen wallpaper
• Communal (Glanceable Hub) -- widget surface accessible from lock screen

---

47.6 Recent Apps

SystemUI does not implement the Recents UI directly. Instead, it delegates to Launcher3 (or a Launcher-based quickstep implementation) through the OverviewProxy pattern.

47.6.1 Recents Architecture

graph LR
    subgraph "SystemUI"
        RC["Recents<br/>(CoreStartable)"]
        RI["RecentsImplementation<br/>(interface)"]
        OPRI["OverviewProxyRecentsImpl"]
        LPS["LauncherProxyService"]
    end
    subgraph "Launcher3 / Quickstep"
        LP["ILauncherProxy"]
        OA["OverviewActivity"]
    end
    RC --> RI
    RI --> OPRI
    OPRI --> LPS
    LPS -.->|Binder| LP
    LP --> OA

47.6.2 OverviewProxyRecentsImpl

The default RecentsImplementation proxies all calls to Launcher:

// frameworks/base/packages/SystemUI/src/com/android/systemui/recents/
//   OverviewProxyRecentsImpl.java
@SysUISingleton
public class OverviewProxyRecentsImpl implements RecentsImplementation {

    @Override
    public void showRecentApps(boolean triggeredFromAltTab) {
        ILauncherProxy launcherProxy = mLauncherProxyService.getProxy();
        if (launcherProxy != null) {
            try {
                launcherProxy.onOverviewShown(triggeredFromAltTab);
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to send overview show event to launcher.", e);
            }
        }
    }

    @Override
    public void toggleRecentApps() {
        ILauncherProxy launcherProxy = mLauncherProxyService.getProxy();
        if (launcherProxy != null) {
            final Runnable toggleRecents = () -> {
                try {
                    mLauncherProxyService.getProxy().onOverviewToggle();
                    mLauncherProxyService.notifyToggleRecentApps();
                } catch (RemoteException e) {
                    Log.e(TAG, "Cannot send toggle recents through proxy service.", e);
                }
            };
            if (mKeyguardStateController.isShowing()) {
                mActivityStarter.executeRunnableDismissingKeyguard(
                        () -> mHandler.post(toggleRecents), null, true, false, true);
            } else {
                toggleRecents.run();
            }
        }
    }
}

47.6.3 LauncherProxyService

The LauncherProxyService maintains the binder connection to Launcher's overview implementation. When the user swipes up from the navigation bar, SystemUI routes the gesture to Launcher, which renders the task thumbnails and handles task switching.

47.6.4 RecentsModule

The Dagger module binds the implementation:

// frameworks/base/packages/SystemUI/src/com/android/systemui/recents/
//   RecentsModule.java
@Module
public abstract class RecentsModule {
    @Binds
    abstract RecentsImplementation bindRecentsImplementation(
            OverviewProxyRecentsImpl impl);
}

---

47.7 Volume Dialog

The volume dialog appears when the user presses hardware volume keys or when system volume changes programmatically.

47.7.1 VolumeDialogControllerImpl

The controller is the source of truth for volume state. It runs on a dedicated background thread:

// frameworks/base/packages/SystemUI/src/com/android/systemui/volume/
//   VolumeDialogControllerImpl.java
@SysUISingleton
public class VolumeDialogControllerImpl implements VolumeDialogController, Dumpable {
    // All work done on a dedicated background worker thread
    // Methods ending in "W" must be called on the worker thread
}

The controller:

• Registers an IVolumeController callback with AudioManager
• Tracks state for multiple audio streams (MUSIC, RING, ALARM, VOICE_CALL, ACCESSIBILITY)
• Monitors ringer mode (normal, vibrate, silent)
• Tracks DND (Do Not Disturb) state
• Manages media sessions for per-app volume

47.7.2 VolumeDialogImpl

The dialog UI is implemented as a Dialog with a custom layout:

// frameworks/base/packages/SystemUI/src/com/android/systemui/volume/
//   VolumeDialogImpl.java  (2,859 lines)
public class VolumeDialogImpl implements VolumeDialog {
    // Window type: TYPE_VOLUME_OVERLAY
    // Displays seekbars for active audio streams
    // Handles ringer mode toggle (ring -> vibrate -> silent)
}

The dialog uses a vertical layout with one SeekBar per active stream:

graph TD
    subgraph "Volume Dialog"
        RS["Ringer Toggle<br/>(ring/vibrate/silent)"]
        MS["Media Stream<br/>SeekBar"]
        RS2["Ring Stream<br/>SeekBar"]
        AS["Alarm Stream<br/>SeekBar"]
        VC["Voice Call Stream<br/>SeekBar"]
        SET["Settings Gear<br/>(link to Sound settings)"]
    end

Key features:

Feature	Implementation
Auto-dismiss	Timeout handler (default 3 seconds)
Live feedback	Updates as system volume changes
CSD warning	CsdWarningDialog for hearing safety
Safety warning	SafetyWarningDialog for media volume
Captions toggle	CaptionsToggleImageButton
Posture-aware	Dismiss on foldable posture change

47.7.3 VolumeDialogComponent

VolumeDialogComponent wires the controller and dialog together as a CoreStartable:

// frameworks/base/packages/SystemUI/src/com/android/systemui/volume/
//   VolumeDialogComponent.java
public class VolumeDialogComponent implements VolumeComponent {
    // Integates VolumeDialogControllerImpl with VolumeDialogImpl
}

47.7.4 Volume Events

The Events class defines all volume-related telemetry events:

// frameworks/base/packages/SystemUI/src/com/android/systemui/volume/Events.java
public class Events {
    public static final int EVENT_SHOW_DIALOG = 0;
    public static final int EVENT_DISMISS_DIALOG = 1;
    public static final int EVENT_ACTIVE_STREAM_CHANGED = 2;
    public static final int EVENT_LEVEL_CHANGED = 3;
    public static final int EVENT_RINGER_TOGGLE = 4;
    // ...
    public static final int DISMISS_REASON_SETTINGS_CLICKED = 7;
    public static final int DISMISS_REASON_POSTURE_CHANGED = 12;
}

---

47.8 Power Menu

The power menu (Global Actions) appears when the user long-presses the power button. It provides options to power off, restart, emergency call, and optionally lockdown.

47.8.1 GlobalActionsComponent

GlobalActionsComponent is the CoreStartable entry point. It uses the plugin extension pattern to allow OEM replacement:

// frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/
//   GlobalActionsComponent.java
@SysUISingleton
public class GlobalActionsComponent
        implements CoreStartable, Callbacks, GlobalActionsManager {

    @Override
    public void start() {
        mBarService = IStatusBarService.Stub.asInterface(
                ServiceManager.getService(Context.STATUS_BAR_SERVICE));
        mExtension = mExtensionController.newExtension(GlobalActions.class)
                .withPlugin(GlobalActions.class)
                .withDefault(mGlobalActionsProvider::get)
                .withCallback(this::onExtensionCallback)
                .build();
        mPlugin = mExtension.get();
        mCommandQueue.addCallback(this);
    }

    @Override
    public void handleShowGlobalActionsMenu() {
        mStatusBarKeyguardViewManager.setGlobalActionsVisible(true);
        mExtension.get().showGlobalActions(this);
    }

    @Override
    public void shutdown() {
        mBarService.shutdown();
    }

    @Override
    public void reboot(boolean safeMode) {
        mBarService.reboot(safeMode);
    }
}

47.8.2 GlobalActionsImpl

The default plugin implementation:

// frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/
//   GlobalActionsImpl.java
public class GlobalActionsImpl implements GlobalActions, CommandQueue.Callbacks {

    @Override
    public void showGlobalActions(GlobalActionsManager manager) {
        if (mDisabled) return;
        mGlobalActionsDialog.showOrHideDialog(
                mKeyguardStateController.isShowing(),
                mDeviceProvisionedController.isDeviceProvisioned(),
                null /* view */,
                mContext.getDisplayId());
    }

    @Override
    public void showShutdownUi(boolean isReboot, String reason) {
        mShutdownUi.showShutdownUi(isReboot, reason);
        mShadeController.instantCollapseShade();
    }

    @Override
    public void disable(int displayId, int state1, int state2, boolean animate) {
        final boolean disabled = (state2 & DISABLE2_GLOBAL_ACTIONS) != 0;
        if (displayId != mContext.getDisplayId() || disabled == mDisabled) return;
        mDisabled = disabled;
        if (disabled) {
            mGlobalActionsDialog.dismissDialog();
        }
    }
}

47.8.3 GlobalActionsDialogLite

At 3,043 lines, GlobalActionsDialogLite implements the actual power menu dialog:

// frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/
//   GlobalActionsDialogLite.java
// Window type: TYPE_STATUS_BAR_SUB_PANEL
// Layout mode: LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS

The dialog dynamically builds its action list based on device capabilities:

graph TD
    subgraph "Power Menu Actions"
        PA["PowerAction<br/>(Power off)"]
        RA["RestartAction<br/>(Restart)"]
        EA["EmergencyAction<br/>(Emergency)"]
        LA["LockDownAction<br/>(Lockdown)"]
        BA["BugReportAction<br/>(Debug builds)"]
        SA["ScreenshotAction"]
    end

Action availability depends on:

Condition	Effect
Device provisioned	All actions available
Keyguard showing	May restrict some actions
User lockdown	Changes lockdown button text
Airplane mode	Affects emergency dialer
Telephony available	Controls emergency action
Debug build	Enables bug report action

47.8.4 ShutdownUi

When a shutdown or reboot is initiated, ShutdownUi displays a full-screen progress animation while the system shuts down. The shade is instantly collapsed to prevent interaction during the shutdown sequence.

47.8.5 Power Menu Layouts

Multiple layout classes support different screen configurations:

GlobalActionsColumnLayout.java   -- Vertical column (phones, portrait)
GlobalActionsFlatLayout.java     -- Horizontal row
GlobalActionsGridLayout.java     -- Grid (tablets)
GlobalActionsLayoutLite.java     -- Base layout logic
GlobalActionsPowerDialog.java    -- Power-specific dialog variant

---

47.9 Screenshots

The screenshot system captures the screen content, displays a preview, and provides editing/sharing actions.

47.9.1 TakeScreenshotService

Screenshot requests arrive from system_server via TakeScreenshotService, a bound service:

// frameworks/base/packages/SystemUI/src/com/android/systemui/screenshot/
//   TakeScreenshotService.java
public class TakeScreenshotService extends Service {
    // Receives screenshot requests from PhoneWindowManager
    // Routes to appropriate handler (headless or interactive)
}

47.9.2 ScreenshotController

ScreenshotController (Kotlin, using @AssistedInject) manages the entire screenshot flow:

// frameworks/base/packages/SystemUI/src/com/android/systemui/screenshot/
//   ScreenshotController.kt
class ScreenshotController @AssistedInject internal constructor(
    appContext: Context,
    screenshotWindowFactory: ScreenshotWindow.Factory,
    viewProxyFactory: ScreenshotShelfViewProxy.Factory,
    screenshotNotificationsControllerFactory:
        ScreenshotNotificationsController.Factory,
    screenshotActionsControllerFactory:
        ScreenshotActionsController.Factory,
    actionExecutorFactory: ActionExecutor.Factory,
    private val screenshotSoundController: ScreenshotSoundController,
    private val uiEventLogger: UiEventLogger,
    private val imageExporter: ImageExporter,
    private val imageCapture: ImageCapture,
    private val scrollCaptureExecutor: ScrollCaptureExecutor,
    // ...
    @Assisted private val display: Display,
) : InteractiveScreenshotHandler {

47.9.3 Screenshot Flow

sequenceDiagram
    participant User
    participant PWM as PhoneWindowManager
    participant TSS as TakeScreenshotService
    participant SC as ScreenshotController
    participant IC as ImageCapture
    participant SW as ScreenshotWindow
    participant IE as ImageExporter
    participant NC as NotificationsController

    User->>PWM: Power + Volume Down
    PWM->>TSS: takeScreenshot()
    TSS->>SC: handleScreenshot()
    SC->>IC: captureDisplay()
    IC-->>SC: Bitmap
    SC->>SW: Show preview window
    SC->>SC: Play shutter sound
    SW->>User: Screenshot preview + actions
    alt User taps Share
        User->>SC: Share action
        SC->>IE: exportToMediaStore()
        IE-->>SC: URI
        SC->>NC: showShareNotification()
    else User taps Edit
        User->>SC: Edit action
        SC->>SC: Launch edit activity
    else Timeout
        SC->>IE: exportToMediaStore()
        IE-->>SC: URI
        SC->>NC: showSavedNotification()
    end

47.9.4 Screenshot Components

Component	Role
ImageCapture / ImageCaptureImpl	Captures screen content as a Bitmap
ScreenshotWindow	Manages the preview overlay window
ScreenshotShelfViewProxy	Preview shelf UI (thumbnail + actions)
ImageExporter	Saves to MediaStore
ScreenshotNotificationsController	Shows save/share notifications
ScreenshotSoundController	Plays camera shutter sound
ScrollCaptureExecutor	Long/scrolling screenshot capture
ScreenshotDetectionController	Notifies apps of screenshot capture
MessageContainerController	Shows work profile messages
TimeoutHandler	Auto-dismisses after timeout
ScreenshotActionsController	Manages action buttons (share, edit)
ActionIntentCreator	Creates intents for share/edit

47.9.5 Long Screenshots

The scroll capture system enables capturing content beyond the visible viewport. ScrollCaptureExecutor communicates with the app's ScrollCaptureCallback to progressively capture tiles of content, which are then stitched together into a single image.

47.9.6 Cross-Profile Screenshots

ScreenshotCrossProfileService handles screenshots that involve managed profile content, using ICrossProfileService to proxy operations across user boundaries.

---

47.10 Multi-Display SystemUI

Modern Android supports multiple displays (external monitors, foldables with two screens, automotive secondary displays). SystemUI must render appropriate UI on each display.

47.10.1 PerDisplayRepository Pattern

The PerDisplayRepository<T> pattern (from com.android.app.displaylib) maintains per-display instances of components:

// frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/
//   PerDisplayRepositoriesModule.kt
@Module
interface PerDisplayRepositoriesModule {
    companion object {
        @SysUISingleton
        @Provides
        fun provideSysUiStateRepository(
            repositoryFactory: PerDisplayInstanceRepositoryImpl.Factory<SysUiState>,
            instanceProvider: SysUIStateInstanceProvider,
        ): PerDisplayRepository<SysUiState> {
            val debugName = "SysUiStatePerDisplayRepo"
            return if (ShadeWindowGoesAround.isEnabled) {
                repositoryFactory.create(debugName, instanceProvider)
            } else {
                DefaultDisplayOnlyInstanceRepositoryImpl(debugName, instanceProvider)
            }
        }
    }
}

When the ShadeWindowGoesAround flag is enabled, components like SysUiState are instantiated per-display. Otherwise, they fall back to default-display-only behaviour.

47.10.2 Per-Display Status Bar

The status bar window controller uses StatusBarWindowControllerStore to manage per-display instances:

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/window/
  StatusBarWindowControllerStore.kt    -- Store for per-display controllers
  StatusBarWindowControllerImpl.java   -- Per-display window management
  StatusBarWindowStateController.kt    -- Per-display window state tracking

Each display gets its own status bar window with appropriate insets and cutout handling.

47.10.3 Per-Display Navigation Bar

NavigationBarControllerImpl manages navigation bars on all displays:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/
//   NavigationBarControllerImpl.java
@SysUISingleton
public class NavigationBarControllerImpl implements
        ConfigurationController.ConfigurationListener,
        NavigationModeController.ModeChangedListener,
        Dumpable, NavigationBarController {

    private final SparseArray<NavigationBar> mNavigationBars = new SparseArray<>();
    // SparseArray keyed by display ID
}

When a new display is added, createNavigationBar() is called. When removed, removeNavigationBar() cleans up.

47.10.4 Display Subcomponent

The SystemUIDisplaySubcomponent provides display-scoped dependencies:

frameworks/base/packages/SystemUI/src/com/android/systemui/display/
  dagger/SystemUIDisplaySubcomponent.java
  data/repository/DisplayComponentRepository.kt

Each display gets its own coroutine scope, configuration controller, and set of display-aware UI components.

graph TD
    subgraph "SysUIComponent (process-wide)"
        DCS["DisplayComponentRepository"]
    end
    subgraph "Display 0 (primary)"
        SB0["StatusBarWindow"]
        NB0["NavigationBar"]
        SS0["SysUiState"]
    end
    subgraph "Display 1 (external)"
        SB1["StatusBarWindow"]
        NB1["NavigationBar"]
        SS1["SysUiState"]
    end
    DCS --> SB0
    DCS --> NB0
    DCS --> SS0
    DCS --> SB1
    DCS --> NB1
    DCS --> SS1

47.10.5 Connected Displays

The StatusBarConnectedDisplays flag gates the expansion of status bar functionality to connected displays. When enabled, CollapsedStatusBarFragment instances are created per-display, each with its own icon pipeline and visibility management.

---

47.11 Navigation Bar

The navigation bar provides the system navigation controls at the bottom (or side) of the screen. It supports three modes: 3-button, 2-button, and fully gestural.

47.11.1 Navigation Mode Controller

NavigationModeController tracks the current navigation mode, which is determined by an overlay package:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/
//   NavigationModeController.java
@SysUISingleton
public class NavigationModeController implements Dumpable {
    public interface ModeChangedListener {
        void onNavigationModeChanged(int mode);
    }
    // Reads navigation mode from overlay applied to
    // com.android.internal.R.integer.config_navBarInteractionMode
}

The three modes are defined in WindowManagerPolicyConstants:

Mode	Constant	Description
3-button	NAV_BAR_MODE_3BUTTON	Back, Home, Recents buttons
2-button	NAV_BAR_MODE_2BUTTON	Back gesture + Home pill
Gestural	NAV_BAR_MODE_GESTURAL	Full gesture navigation

47.11.2 NavigationBarView

NavigationBarView is the root view for the navigation bar:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/views/
//   NavigationBarView.java
public class NavigationBarView extends FrameLayout
        implements Gefingerpoken {
    // Contains ButtonDispatchers for Home, Back, Recents
    // Manages rotation, layout direction, and button visibility
}

The view uses ButtonDispatcher to abstract button behaviour across different button implementations (physical, software, or gesture targets):

graph TD
    NBV["NavigationBarView"]
    NBV --> NBIV["NavigationBarInflaterView<br/>(inflates button layout)"]
    NBIV --> BD_Back["ButtonDispatcher<br/>(Back)"]
    NBIV --> BD_Home["ButtonDispatcher<br/>(Home)"]
    NBIV --> BD_Recents["ButtonDispatcher<br/>(Recents)"]
    NBIV --> BD_IME["ContextualButton<br/>(IME Switcher)"]
    NBIV --> BD_Rotate["ContextualButton<br/>(Rotation Suggestion)"]
    NBIV --> BD_A11y["ContextualButton<br/>(Accessibility)"]

47.11.3 NavigationBarInflaterView

The button layout is defined by a string spec that NavigationBarInflaterView parses:

// Default 3-button layout spec:
"back[1.0];home;recent[1.0]"

// 2-button layout spec:
"back[1.0];home;contextual[1.0]"

// Gestural layout (minimal):
"home_handle"

This allows OEMs to customise button order and sizes through overlays.

47.11.4 Gesture Navigation

In gestural mode, the navigation bar is replaced by a thin home indicator handle. Navigation gestures are handled by EdgeBackGestureHandler:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/
//   gestural/EdgeBackGestureHandler.java
public class EdgeBackGestureHandler implements DisplayManager.DisplayListener,
        NavigationModeController.ModeChangedListener {
    // Handles edge swipe gestures for back navigation
    // Manages gesture exclusion zones
    // Integrates with predictive back animation
}

The gesture system:

graph TD
    subgraph "Gesture Navigation"
        EBG["EdgeBackGestureHandler"]
        EBG --> ML["ML Classifier<br/>(BackGestureTfClassifierProvider)"]
        EBG --> BP["BackPanelController<br/>(visual feedback)"]
        EBG --> WM["WindowManager<br/>(gesture exclusion)"]
        EBG --> FC["FalsingCollector<br/>(prevent false triggers)"]
    end

Edge back gesture detection:

1. The handler registers an input monitor for the display edges
2. When a touch starts within the edge zone (typically 24dp), tracking begins
3. A TensorFlow Lite classifier evaluates whether the gesture is a back swipe or an app gesture (e.g., drawer open)
4. If classified as back, the BackPanelController shows the visual arrow
5. The gesture is dispatched as a BackEvent to the focused window
6. If predictive back is enabled, the app can animate in response

47.11.5 DisplayBackGestureHandler

For multi-display support, DisplayBackGestureHandler wraps the per-display gesture handling:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/
//   gestural/DisplayBackGestureHandler.kt
// Per-display back gesture handling

47.11.6 NavigationBarTransitions

NavigationBarTransitions manages the visual transitions of the navigation bar between modes:

// Transition modes:
MODE_OPAQUE         -- Solid background (default)
MODE_SEMI_TRANSPARENT  -- Partially transparent
MODE_TRANSLUCENT    -- Fully transparent with scrim
MODE_LIGHTS_OUT     -- Dimmed (immersive mode)
MODE_TRANSPARENT    -- Fully transparent

47.11.7 Taskbar Integration

On large screens (tablets, foldables), the traditional navigation bar may be replaced by a taskbar provided by Launcher. TaskbarDelegate in SystemUI coordinates with the Launcher-provided taskbar:

// frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/
//   TaskbarDelegate.java
public class TaskbarDelegate implements // ...
    // Routes navigation bar callbacks to the Launcher taskbar
    // Falls back to traditional nav bar when Launcher is unavailable

The enableTaskbarOnPhones feature flag controls whether the taskbar is also available on phone form factors.

---

47.12 Monet / Dynamic Color / Material You

Android 12 introduced Material You, a design language where the entire system UI derives its colour palette from the user's wallpaper. The engine behind this is called Monet -- a colour-science pipeline that extracts a seed colour from WallpaperColors, generates tonal palettes through the Material Color Utilities library, and applies the resulting colours as fabricated resource overlays across every package.

47.12.1 End-to-End Pipeline

graph TB
    subgraph "Wallpaper Stack"
        WP[WallpaperManager]
        WC["WallpaperColors<br/>Primary / Secondary / Tertiary<br/>+ allColors population map"]
    end

    subgraph "SystemUI -- ThemeOverlayController"
        TOC["ThemeOverlayController<br/>CoreStartable"]
        SEED["getSeedColor()<br/>ColorScheme.getSeedColors()"]
        CS_DARK["ColorScheme<br/>(dark)"]
        CS_LIGHT["ColorScheme<br/>(light)"]
        FAB["FabricatedOverlay x3<br/>accent / neutral / dynamic"]
    end

    subgraph "Monet Library"
        HCT["Hct.fromInt(seed)"]
        SCHEME["DynamicScheme<br/>TonalSpot / Vibrant /<br/>Expressive / Neutral / ..."]
        TP["TonalPalette<br/>13 shade stops<br/>0..1000"]
    end

    subgraph "OverlayManager"
        OM["OverlayManagerService"]
        RES["android.R.color.system_*"]
    end

    subgraph "All Apps"
        APPS["Apps read<br/>system_accent1_500,<br/>system_neutral1_100, ..."]
    end

    WP -->|"onColorsChanged"| TOC
    TOC --> SEED
    SEED --> HCT
    HCT --> SCHEME
    SCHEME --> TP
    TP --> CS_DARK
    TP --> CS_LIGHT
    CS_DARK --> FAB
    CS_LIGHT --> FAB
    TOC -->|"applyCurrentUserOverlays()"| OM
    FAB --> OM
    OM -->|"registerFabricatedOverlay"| RES
    RES --> APPS

47.12.2 Colour Extraction -- Seed Selection

ColorScheme.getSeedColors() implements the Monet seed-selection algorithm. Given WallpaperColors (which contains all quantized colours with population data), it:

1. Builds a hue histogram -- 360 slots, each accumulating the proportion of colours with that hue.
2. Scores each colour by a weighted combination of hue proportion (70%) and chroma distance from the 48.0 target (30%).
3. Filters low-chroma colours (chroma < 5) which would produce grey themes.
4. Selects hue-distinct seeds -- iteratively reduces the minimum hue distance from 90 degrees down to 15, picking up to 4 seeds.
5. Falls back to GOOGLE_BLUE (0xFF1b6ef3) if no suitable colour exists.

// frameworks/libs/systemui/monet/src/com/android/systemui/monet/ColorScheme.java
public static List<Integer> getSeedColors(WallpaperColors wallpaperColors, boolean filter) {
    // ...
    // Score: 0.7 * hueProportion + 0.3 * (chroma - 48)
    // Iterative hue-distance selection from 90° down to 15°
    // Fallback: GOOGLE_BLUE
}

For Live Wallpapers where quantization population is zero, the method trusts the ordering of the three main colours directly, filtering only by minimum chroma.

47.12.3 The ColorScheme Class

ColorScheme wraps the Material Color Utilities DynamicScheme and exposes six TonalPalette instances:

// frameworks/libs/systemui/monet/src/com/android/systemui/monet/ColorScheme.java
@Deprecated  // migrating to MaterialDynamicColors
public class ColorScheme {
    private final TonalPalette mAccent1;   // primaryPalette
    private final TonalPalette mAccent2;   // secondaryPalette
    private final TonalPalette mAccent3;   // tertiaryPalette
    private final TonalPalette mNeutral1;  // neutralPalette
    private final TonalPalette mNeutral2;  // neutralVariantPalette
    private final TonalPalette mError;     // errorPalette
}

Each palette is constructed from Hct (Hue-Chroma-Tone) colour space via the Material library's TonalPalette. The class delegates to a style-specific DynamicScheme based on ThemeStyle:

ThemeStyle	DynamicScheme	Character
TONAL_SPOT	SchemeTonalSpot	Default -- balanced, moderate chroma
VIBRANT	SchemeVibrant	Higher chroma for bolder colours
EXPRESSIVE	SchemeExpressive	Maximum chromatic variety
SPRITZ	SchemeNeutral	Desaturated, subdued
RAINBOW	SchemeRainbow	Full hue rotation
FRUIT_SALAD	SchemeFruitSalad	Playful multi-hue
CONTENT	SchemeContent	Faithful to source image
MONOCHROMATIC	SchemeMonochrome	Single-hue grayscale
CLOCK	SchemeClock	Custom SystemUI scheme for lock screen clocks
CLOCK_VIBRANT	SchemeClockVibrant	High-chroma clock variant

47.12.4 TonalPalette and Shade Stops

Each TonalPalette contains 13 tonal stops:

// frameworks/libs/systemui/monet/src/com/android/systemui/monet/TonalPalette.java
public static final List<Integer> SHADE_KEYS =
    Arrays.asList(0, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000);

Shade 0 is white, shade 1000 is black. The getAtTone(shade) method maps the 0-1000 range to the Material library's 0-100 tone scale via (1000 - shade) / 10. This produces Android's system_accent1_0 through system_accent1_1000 resource colours.

47.12.5 ThemeOverlayController -- The Orchestrator

ThemeOverlayController is a CoreStartable that wires together wallpaper change detection, colour scheme generation, and overlay application:

// frameworks/base/packages/SystemUI/src/com/android/systemui/theme/
//   ThemeOverlayController.java
@SysUISingleton
public class ThemeOverlayController implements CoreStartable, Dumpable {
    // Key fields:
    protected ColorScheme mColorScheme;
    protected int mMainWallpaperColor = Color.TRANSPARENT;
    private int mThemeStyle = ThemeStyle.TONAL_SPOT;
    private double mContrast = 0.0;
    private FabricatedOverlay mAccentOverlay;
    private FabricatedOverlay mNeutralOverlay;
    private FabricatedOverlay mDynamicOverlay;
}

Listeners registered on start():

Listener	Purpose
WallpaperManager.OnColorsChangedListener	Detects wallpaper colour changes for all users
SecureSettings ContentObserver	Detects THEME_CUSTOMIZATION_OVERLAY_PACKAGES changes
UserTracker.Callback	Re-evaluates on user switch
UiModeManager.ContrastChangeListener	Re-evaluates when contrast level changes
BroadcastReceiver for ACTION_PROFILE_ADDED	Applies overlays to new managed profiles
BroadcastReceiver for ACTION_WALLPAPER_CHANGED	Re-enables colour event acceptance
KeyguardTransitionInteractor (asleep state)	Defers processing until screen off

47.12.6 Colour Event Deferral

The controller uses a sophisticated deferral mechanism to avoid jarring mid-use colour changes. When the user is looking at the screen, colour events are suppressed until the display goes off:

sequenceDiagram
    participant WM as WallpaperManager
    participant TOC as ThemeOverlayController
    participant KTI as KeyguardTransitionInteractor
    participant OMS as OverlayManagerService

    WM->>TOC: onColorsChanged(colors, userId)
    alt Screen is ON and acceptColorEvents=false
        TOC->>TOC: mDeferredWallpaperColors.put(userId, colors)
        Note over TOC: "Deferred until screen off"
    else acceptColorEvents=true
        TOC->>TOC: mAcceptColorEvents = false
        TOC->>TOC: handleWallpaperColors()
        TOC->>TOC: reevaluateSystemTheme()
    end

    KTI-->>TOC: isFinishedIn(DOZING) = true
    TOC->>TOC: Process deferred colours
    TOC->>TOC: createOverlays(seedColor)
    TOC->>OMS: applyCurrentUserOverlays()

The wallpaper picker sets EXTRA_FROM_FOREGROUND_APP=true on the ACTION_WALLPAPER_CHANGED broadcast, which resets mAcceptColorEvents to true -- so user-initiated changes apply immediately.

47.12.7 Overlay Creation and Application

The createOverlays() method produces three fabricated overlays:

private void createOverlays(int color) {
    mDarkColorScheme = new ColorScheme(color, true, mThemeStyle, mContrast);
    mLightColorScheme = new ColorScheme(color, false, mThemeStyle, mContrast);

    mAccentOverlay = newFabricatedOverlay("accent");
    assignColorsToOverlay(mAccentOverlay, DynamicColors.getAllAccentPalette(), false);

    mNeutralOverlay = newFabricatedOverlay("neutral");
    assignColorsToOverlay(mNeutralOverlay, DynamicColors.getAllNeutralPalette(), false);

    mDynamicOverlay = newFabricatedOverlay("dynamic");
    assignColorsToOverlay(mDynamicOverlay, DynamicColors.getAllDynamicColorsMapped(), false);
    assignColorsToOverlay(mDynamicOverlay, DynamicColors.getFixedColorsMapped(), true);
    assignColorsToOverlay(mDynamicOverlay, DynamicColors.getCustomColorsMapped(), false);
}

For themed (non-fixed) colours, each resource has _light and _dark variants:

overlay.setResourceValue(prefix + "_light", TYPE_INT_COLOR_ARGB8,
    p.second.getArgb(mLightColorScheme.getMaterialScheme()), null);
overlay.setResourceValue(prefix + "_dark", TYPE_INT_COLOR_ARGB8,
    p.second.getArgb(mDarkColorScheme.getMaterialScheme()), null);

Fixed colours (e.g. primaryFixed) are not dark/light variant and use the light scheme only.

47.12.8 DynamicColors Token Mapping

The DynamicColors class generates the full set of colour tokens:

// frameworks/libs/systemui/monet/src/com/android/systemui/monet/DynamicColors.java
public class DynamicColors {
    // Palette colours: accent1_0..1000, accent2_*, accent3_*, neutral1_*, neutral2_*
    public static List<Pair<String, DynamicColor>> getAllAccentPalette();
    public static List<Pair<String, DynamicColor>> getAllNeutralPalette();

    // Material Dynamic Colors: primary, onPrimary, primaryContainer, ...
    public static List<Pair<String, DynamicColor>> getAllDynamicColorsMapped();

    // Fixed colours: primaryFixed, secondaryFixed, ...
    public static List<Pair<String, DynamicColor>> getFixedColorsMapped();

    // Custom SystemUI-specific colours
    public static List<Pair<String, DynamicColor>> getCustomColorsMapped();
}

The token names are mapped to Android resource names with the prefix android:color/system_. For example, accent1_500 becomes android:color/system_accent1_500.

47.12.9 ThemeOverlayApplier -- The Transaction

ThemeOverlayApplier takes the fabricated overlays and applies them via OverlayManager in a single atomic transaction:

// frameworks/base/packages/SystemUI/src/com/android/systemui/theme/
//   ThemeOverlayApplier.java
@SysUISingleton
public class ThemeOverlayApplier implements Dumpable {
    // Overlay categories applied in order:
    static final List<String> THEME_CATEGORIES = Lists.newArrayList(
        OVERLAY_CATEGORY_SYSTEM_PALETTE,    // Tonal palette
        OVERLAY_CATEGORY_ICON_LAUNCHER,     // Launcher icons
        OVERLAY_CATEGORY_SHAPE,             // Adaptive icon shape
        OVERLAY_CATEGORY_FONT,              // System font
        OVERLAY_CATEGORY_ACCENT_COLOR,      // Accent colour
        OVERLAY_CATEGORY_DYNAMIC_COLOR,     // Dynamic Material colours
        OVERLAY_CATEGORY_ICON_ANDROID,      // Framework icons
        OVERLAY_CATEGORY_ICON_SYSUI,        // SystemUI icons
        OVERLAY_CATEGORY_ICON_SETTINGS,     // Settings icons
        OVERLAY_CATEGORY_ICON_THEME_PICKER  // Theme picker icons
    );
}

The applier first disables all currently enabled overlays in the affected categories, then registers new fabricated overlays, and enables them -- all in a single OverlayManagerTransaction to minimise configuration changes.

Categories in SYSTEM_USER_CATEGORIES are applied to both the current user and user 0 (system user), ensuring SystemUI and framework processes see the correct colours.

47.12.10 Settings Integration

Theme customisation is persisted in Settings.Secure.THEME_CUSTOMIZATION_OVERLAY_PACKAGES as a JSON object:

{
  "android.theme.customization.system_palette": "1b6ef3",
  "android.theme.customization.accent_color": "1b6ef3",
  "android.theme.customization.color_source": "home_wallpaper",
  "android.theme.customization.theme_style": "TONAL_SPOT",
  "android.theme.customization.color_both": "1",
  "_applied_timestamp": 1234567890
}

The ThemeOverlayController monitors this setting and re-evaluates on every change. When the wallpaper changes and no preset colour is selected, it updates this setting automatically, recording the colour source and timestamp.

47.12.11 Hardware Default Colours

Starting with Android 15, the hardwareColorStyles flag enables OEMs to provide device-specific default colour palettes during the Setup Wizard. Before the device is provisioned, the controller reads hardware defaults (seed colour + style + source) and persists them as the initial theme setting.

47.12.12 Contrast Support

ThemeOverlayController integrates with UiModeManager.getContrast() to apply Material Design contrast levels. When the user changes the display contrast in Accessibility settings, the controller receives a callback, passes the new contrast value to ColorScheme, and regenerates overlays:

// In ColorScheme constructor:
new ColorScheme(seed, isDark, mThemeStyle, mContrast)
// mContrast flows through to DynamicScheme's contrastLevel parameter

This adjusts the tonal mapping so that foreground/background colour pairs maintain the selected contrast ratio.

47.12.13 Key Source Paths (Monet)

Path	Description
frameworks/libs/systemui/monet/src/com/android/systemui/monet/ColorScheme.java	Seed selection, palette generation
frameworks/libs/systemui/monet/src/com/android/systemui/monet/TonalPalette.java	13-stop tonal palette wrapper
frameworks/libs/systemui/monet/src/com/android/systemui/monet/DynamicColors.java	Token-to-DynamicColor mapping
frameworks/libs/systemui/monet/src/com/android/systemui/monet/CustomDynamicColors.java	SystemUI-specific custom tokens
frameworks/libs/systemui/monet/src/com/android/systemui/monet/Shades.java	Legacy shade generation
frameworks/libs/systemui/monet/src/com/android/systemui/monet/SchemeClock.java	Clock face colour scheme
frameworks/libs/systemui/monet/src/com/android/systemui/monet/SchemeClockVibrant.java	Vibrant clock variant
frameworks/base/packages/SystemUI/src/com/android/systemui/theme/ThemeOverlayController.java	Orchestrator (CoreStartable)
frameworks/base/packages/SystemUI/src/com/android/systemui/theme/ThemeOverlayApplier.java	OverlayManager transaction
frameworks/base/packages/SystemUI/src/com/android/systemui/theme/ThemeModule.java	Dagger module

---

47.13 Window Manager Shell Deep Dive

Section 47.1.2 mentioned that SystemUI receives "shell interfaces" — Pip, SplitScreen, Bubbles, ShellTransitions — from a separate Dagger subcomponent called WMComponent. That subcomponent and the code behind those interfaces live in their own AOSP library at frameworks/base/libs/WindowManager/Shell, called WM Shell throughout the codebase (Java package com.android.wm.shell). This section walks through what WM Shell is, how it integrates with SystemUI, and how its per-feature subpackages map to the multi-window experiences a user sees on screen.

47.13.1 Shell Is a Library, Not a Process

The name "shell" can mislead. WM Shell does not run as a separate process — there is no wm_shell entry in ps. It is a Java library (wm_shell-sources filegroup in frameworks/base/libs/WindowManager/Shell/Android.bp) that the SystemUI APK statically links and loads into its own process. The "shell" name reflects its conceptual role: a shell around the WindowManagerService core, providing the policy and UI for windowing features without bloating system_server.

This division has a concrete reason. Multi-window UX (PIP windows, split view dividers, freeform window decorations, bubble badges) needs to render Views, listen to gestures, and react to configuration changes — work that naturally belongs in a foreground UI process rather than the system server. SystemUI is already a long-lived foreground process with rendering, input, and IPC plumbing in place, so the Shell library piggy-backs on it. On Wear, TV, or Auto, a different SystemUI variant links a different form-factor Shell module (see 47.13.7), but the loading mechanism is the same.

flowchart LR
    subgraph SystemServer["system_server process"]
        WMS["WindowManagerService<br/>(window tree, layout)"]
        ATM["ActivityTaskManagerService"]
        ITaskOrg["ITaskOrganizerController<br/>(Binder)"]
        WMS --> ITaskOrg
        ATM --> WMS
    end
    subgraph SystemUI["systemui process"]
        WMComponent["WMComponent<br/>(Dagger subcomponent)"]
        ShellInterface["ShellInterface<br/>(lifecycle facade)"]
        ShellTaskOrg["ShellTaskOrganizer<br/>(extends TaskOrganizer)"]
        Features["pip/<br/>splitscreen/<br/>bubbles/<br/>freeform/<br/>desktopmode/<br/>onehanded/<br/>recents/<br/>transition/<br/>startingsurface"]
        SysUI["SysUI components<br/>(WMShell adapter, QS, NotifShade, ...)"]
        WMComponent --> ShellInterface
        WMComponent --> ShellTaskOrg
        WMComponent --> Features
        ShellInterface --> SysUI
        Features --> SysUI
    end
    ShellTaskOrg <-.Binder.-> ITaskOrg

The right-hand process loads the entire Shell library; the left-hand process owns the source of truth for what windows exist. They communicate through one Binder interface (ITaskOrganizerController) plus a handful of event listeners.

47.13.2 WMComponent: Shell's Dagger Boundary

WM Shell exposes a strict surface to SystemUI through the WMComponent Dagger subcomponent:

// Source: frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/
//   dagger/WMComponent.java:56
@WMSingleton
@Subcomponent(modules = {WMShellModule.class})
public interface WMComponent {

    default void init() {
        getShell().onInit();
    }

    // Interfaces provided to SysUI
    @WMSingleton ShellInterface getShell();
    @WMSingleton Optional<OneHanded> getOneHanded();
    @WMSingleton Optional<Pip> getPip();
    @WMSingleton Optional<SplitScreen> getSplitScreen();
    @WMSingleton Optional<Bubbles> getBubbles();
    @WMSingleton Optional<TaskViewFactory> getTaskViewFactory();
    @WMSingleton ShellTransitions getShellTransitions();
    @WMSingleton KeyguardTransitions getKeyguardTransitions();
    @WMSingleton Optional<StartingSurface> getStartingSurface();
    @WMSingleton Optional<DisplayAreaHelper> getDisplayAreaHelper();
    @WMSingleton Optional<RecentTasks> getRecentTasks();
    @WMSingleton Optional<BackAnimation> getBackAnimation();
    @WMSingleton Optional<DesktopMode> getDesktopMode();
    @WMSingleton Optional<AppZoomOut> getAppZoomOut();
    @WMSingleton Optional<AppHandles> getAppHandles();
    // ... plus a few injector methods for field injection
}

Two design rules show in this signature:

• Almost everything is Optional<>. PIP only exists on form factors that allow it. Split-screen is absent on watches. RecentTasks is present on phones but consumed by Launcher, not SystemUI directly. Wrapping every feature in Optional lets the same SystemUI codebase build across phones, tablets, TV, Wear, and Auto.
• The component lists Dagger modules, not classes. WMComponent installs WMShellModule. The TV variant TvWMComponent installs TvWMShellModule instead, which binds different implementations of the same Pip / Bubbles / etc. interfaces. The interface contract with SystemUI is identical; the implementation is form-factor specific.

The @WMSingleton scope ensures each feature gets exactly one instance per Shell. WMSingleton is a custom Dagger scope defined in WMSingleton.java — it is not @Singleton, because the SysUI side has its own @SysUISingleton, and the two scopes need to coexist in the same process without colliding.

47.13.3 ShellInterface: The Lifecycle Facade

Most features live behind their own type, but the Shell as a whole is exposed through a single facade called ShellInterface:

// Source: frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/
//   sysui/ShellInterface.java:34
public interface ShellInterface {
    default void onInit() {}
    default void onConfigurationChanged(Configuration newConfiguration) {}
    default void onKeyguardVisibilityChanged(boolean visible, boolean occluded,
            boolean animatingDismiss) {}
    default void onKeyguardDismissAnimationFinished() {}
    default void onUserChanged(int newUserId, @NonNull Context userContext) {}
    default void onUserProfilesChanged(@NonNull List<UserInfo> profiles) {}
    default void addDisplayImeChangeListener(DisplayImeChangeListener listener,
            Executor executor) {}
    default void removeDisplayImeChangeListener(DisplayImeChangeListener listener) {}
    // ... handles shell commands, dumps, etc.
}

The interface mirrors the lifecycle events SystemUI already tracks (keyguard visibility, user changes, configuration changes, IME position). The implementation is ShellController, which fans these events out to each registered Shell feature.

This shape means the Shell does not poll SystemUI; SystemUI pushes state changes. The SysUI-side adapter is com.android.systemui.wmshell.WMShell, a @SysUISingleton CoreStartable whose start() method wires every SystemUI signal SystemUI emits — KeyguardStateController, WakefulnessLifecycle, ConfigurationController, UserTracker, CommandQueue — to the corresponding ShellInterface method.

47.13.4 ShellInit: Ordered Initialization

A library injected by Dagger has a known construction order (driven by the dependency graph), but Dagger does not guarantee a known initialization order. ShellInit adds that guarantee:

// Source: frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/
//   sysui/ShellInit.java:62
public <T extends Object> void addInitCallback(Runnable r, T instance) {
    if (mHasInitialized) {
        if (Build.isDebuggable()) {
            // All callbacks must be added prior to the Shell being initialized
            throw new IllegalArgumentException("Can not add callback after init");
        }
        return;
    }
    final String className = instance.getClass().getSimpleName();
    mInitCallbacks.add(new Pair<>(className, r));
    ProtoLog.v(WM_SHELL_INIT, "Adding init callback for %s", className);
}

@VisibleForTesting
public void init() {
    ProtoLog.v(WM_SHELL_INIT, "Initializing Shell Components: %d", mInitCallbacks.size());
    SurfaceControl.setDebugUsageAfterRelease(true);
    // Init in order of registration
    for (int i = 0; i < mInitCallbacks.size(); i++) {
        final Pair<String, Runnable> info = mInitCallbacks.get(i);
        final long t1 = SystemClock.uptimeMillis();
        info.second.run();
        final long t2 = SystemClock.uptimeMillis();
        ProtoLog.v(WM_SHELL_INIT, "\t%s init took %dms", info.first, (t2 - t1));
    }
    mInitCallbacks.clear();
    mHasInitialized = true;
}

Each Shell component injects ShellInit in its constructor and calls addInitCallback(this::onInit, this). Because Dagger constructs the graph leaves-first, the callbacks land in dependency order automatically. When WMComponent.init() later fires getShell().onInit(), ShellController calls ShellInit.init(), which drains the queue in registration order. The per-component init time is logged through ProtoLog (see 47.13.10) so regressions in Shell start-up cost show up in traces.

In debug builds, adding a callback after init() throws. This is a deliberate guard: late init usually means a feature got constructed through lazy injection on the main thread instead of at component build-time, which would defeat the dependency-ordered startup.

47.13.5 ShellTaskOrganizer: The Bridge to WindowManager

Shell features need to observe and manipulate the system's task tree: PIP needs to know when a task enters picture-in-picture mode, split-screen needs to reparent tasks under its divider, transitions need to inspect what just appeared. system_server's ActivityTaskManagerService exposes that observation surface through the TaskOrganizer API, and ShellTaskOrganizer is the Shell's single implementation of it:

// Source: frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/
//   ShellTaskOrganizer.java:90
public class ShellTaskOrganizer extends TaskOrganizer {
    // ...
    public ShellTaskOrganizer(ShellInit shellInit, /* ... */) {
        super(/* ... */);
        // wait to register until Transitions is initialized
        shellInit.addInitCallback(this::onInit, this);
    }

    @Override
    public List<TaskAppearedInfo> registerOrganizer() {
        synchronized (mLock) {
            final List<TaskAppearedInfo> taskInfos = super.registerOrganizer();
            // ... rebroadcast current tasks to Shell listeners
            return taskInfos;
        }
    }
}

TaskOrganizer is an AOSP-internal Binder interface. When the Shell calls registerOrganizer(), system_server starts pushing onTaskAppeared / onTaskInfoChanged / onTaskVanished callbacks back to the Shell process. The Shell maintains a single registration — features like PIP and split-screen don't each register their own TaskOrganizer; they subscribe to ShellTaskOrganizer via per-feature listener interfaces. That keeps the IPC channel narrow and avoids duplicate notifications for the same window event.

47.13.6 Per-Feature Subpackages

The Shell groups each multi-window experience under its own package. The following table maps the visible features to their source locations:

Package under com.android.wm.shell.	What the user sees
pip/, pip2/	Picture-in-picture video windows. pip2 is the staged rewrite of the legacy pip package.
splitscreen/	Side-by-side or top-bottom split with the central drag divider.
bubbles/	Floating conversation bubbles + the bubble bar.
freeform/	Free-floating, resizable windows on large screens.
desktopmode/	Connected-display desktop with multiple visible app windows.
onehanded/	One-handed mode that drags the screen contents downward.
back/	Predictive back animation (system & cross-activity).
transition/	Cross-activity / cross-task transitions driven by Shell.
startingsurface/	App splash screens and snapshot starting windows.
recents/	Recent-tasks data feed to Launcher.
windowdecor/	Title bars / handles on freeform & desktop windows.
compatui/	Restart-for-resize and aspect-ratio-mismatch buttons.
taskview/	The TaskView reusable view that hosts a task inside another window.
unfold/	Foldable unfold/fold animation pipeline.
activityembedding/	Jetpack ActivityEmbedding host-side support.
keyguard/	KeyguardTransitions — Shell's slice of keyguard show/hide animations.
apptoweb/	Web-link launch helpers for embedded browsing.
appzoomout/	Zoomed-out app overview used by Recents.
hidedisplaycutout/	Lets apps opt the cutout into a black bar.
crashhandling/	Surface-level crash overlay during AppCrash.

Each subpackage owns its model, its UI (often a Compose or View tree that renders inside a Shell-owned window), and its public interface in WMComponent. Cross-package interactions go through Shell-internal contracts (Transitions, ShellTaskOrganizer listeners, ShellController callbacks) rather than direct calls — the same isolation discipline that keeps WMComponent's surface minimal applies inside the library too.

47.13.7 Form-Factor Variants: WMShellModule vs TvWMShellModule

The same WMComponent interface is satisfied by different Dagger modules depending on the build target. The largest module is WMShellModule (~phone/tablet/foldable behaviour); TV builds substitute TvWMShellModule, which binds TV-specific PIP, TV-style transitions, and disables features that do not apply (split-screen, freeform). The TV variant is selected through TvWMComponent:

// Conceptually:
//   WMComponent       includes WMShellModule
//   TvWMComponent     includes TvWMShellModule

A SystemUI build picks one or the other based on its product flavour. Wear and Auto plug in their own variants the same way. OEMs that ship a custom form factor (Chromebook, AR headset, …) typically add another Subcomponent rather than forking the Shell library, because every variant still benefits from upstream feature work going into the base WMShellModule.

The base module WMShellBaseModule is shared across variants and runs to ~1200 lines: it binds the transports (ShellExecutor, HandlerThread, Choreographer), the cross-cutting services (ShellInit, ShellController, ShellCommandHandler, ProtoLogController, ShellTaskOrganizer, Transitions, DisplayController), and a long list of providers for things every form factor needs (back animation, drag-and-drop, splash screens, IME position tracking).

47.13.8 Transitions: Driving Animations from Shell

Pre-Android-12, cross-activity animations were driven by system_server with hardcoded animations baked into WindowManagerService. The modern model moves the animation implementation into Shell, while system_server still owns the decision to start an animation. The plumbing lives in com.android.wm.shell.transition.Transitions:

• system_server calls IShellTransitions#onTransitionReady(...) over Binder, handing the Shell a TransitionInfo that lists the windows appearing / disappearing / changing.
• Transitions matches the info against registered TransitionHandlers in priority order. The first handler that accepts becomes the animator for that transition.
• The handler manipulates SurfaceControls and runs animators on the Shell main thread. When the animation finishes, the Shell calls finishTransition(...) back to system_server, which then applies the queued WindowContainerTransaction.

Each feature that wants custom motion (PIP enter/exit, split-screen divider drag, desktop window animate, predictive back) registers its own TransitionHandler. The Shell's central DefaultTransitionHandler is the fallback when nothing else handles the transition.

ShellTransitions is the small interface SystemUI receives through WMComponent (getShellTransitions()); it exposes only the hooks that SystemUI needs (e.g. registering its own handlers for shade and keyguard animations) and hides the internals.

47.13.9 TaskView: Embedding a Task in a View

taskview/ provides one of the Shell's most reused primitives: a TaskView that hosts a real task inside a regular View. Bubbles use it to render the conversation app inside the expanded bubble window. Settings panels use it for embedded preferences. Apps with the right permission use it for trusted overlays.

Internally, TaskViewFactory is the @WMSingleton factory exposed through WMComponent. It creates TaskViewTaskController and a SurfaceControl-backed TaskView View, registers the task with ShellTaskOrganizer, and re-parents its surface under the View when the task appears. Resize and bounds updates flow through WindowContainerTransactions back to system_server. The visible result is that a single child View shows another app's UI while the host process still owns input dispatch above the surface.

47.13.10 ProtoLog: Build-Time Log Transformation

Shell logging is unusual: it does not call Log.d(TAG, ...) directly. Instead, every log call goes through ProtoLog, and a build-time tool (protologtool, defined in Android.bp) rewrites the calls into a compact binary form. The rewrite is driven by ShellProtoLogGroup and the wm_shell_protolog-groups Java library.

// Source: frameworks/base/libs/WindowManager/Shell/Android.bp:65
java_genrule {
    name: "wm_shell_protolog_src",
    srcs: [
        ":protolog-impl",
        ":wm_shell-sources",
        ":wm_shell_protolog-groups",
    ],
    tools: ["protologtool"],
    cmd: "$(location protologtool) transform-protolog-calls " +
        "--protolog-class com.android.internal.protolog.ProtoLog " +
        "--loggroups-class com.android.wm.shell.protolog.ShellProtoLogGroup " +
        "--loggroups-jar $(location :wm_shell_protolog-groups) " +
        "--viewer-config-file-path /system_ext/etc/wmshell.protolog.pb " +
        "--output-srcjar $(out) " +
        "$(locations :wm_shell-sources)",
    out: ["wm_shell_protolog.srcjar"],
}

The build emits two artefacts:

• A .srcjar of rewritten Shell sources, where each ProtoLog.v(GROUP, "format", args) becomes a numeric ID plus its arg values, dropping the format string from the runtime binary.
• wmshell.protolog.pb (installed into /system_ext/etc/), a protobuf-encoded map from log ID back to format string.

This split keeps Shell log statements cheap (one ID + args, no string work in the hot path) while still letting dumpsys and trace tools reconstruct human-readable lines on demand. Chapter 56's tracing section covers ProtoLog in detail; for Shell purposes, the key point is that greping the Shell source for human log text returns the pre-transform code, which is what developers read and review.

47.13.11 The Jetpack Half (libs/WindowManager/Jetpack)

The sibling frameworks/base/libs/WindowManager/Jetpack/ directory is not part of the Shell library. It implements androidx.window.extensions.* — the platform side of the AndroidX WindowManager Jetpack library — and ships as androidx.window.extensions on the device. Apps that depend on androidx.window (foldable posture APIs, ActivityEmbedding, area extensions) talk to this extensions APK, which in turn talks to the platform.

Source: frameworks/base/libs/WindowManager/Jetpack/src/androidx/window/extensions/ (WindowExtensionsImpl.java, WindowExtensionsProvider.java, plus area/, bubble/, embedding/, layout/, util/ subpackages).

The two libraries share a parent directory because they share a domain (WindowManager-adjacent client code) and historically share contributors, but they are otherwise independent: the Shell runs inside SystemUI; the Jetpack extensions library is loaded into each app's process via the extensions discovery API.

47.13.12 How SystemUI Talks Back to Shell: The WMShell CoreStartable

The SystemUI side has a single adapter that wires SystemUI's state into Shell's listeners:

// Source: frameworks/base/packages/SystemUI/src/com/android/systemui/wmshell/
//   WMShell.java:99
@SysUISingleton
public final class WMShell implements CoreStartable, CommandQueue.Callbacks {
    // Injected: ShellInterface, Optional<Pip>, Optional<SplitScreen>,
    //           Optional<Bubbles>, Optional<OneHanded>, Optional<RecentTasks>,
    //           Optional<DesktopMode>, KeyguardStateController,
    //           WakefulnessLifecycle, ConfigurationController, ...
}

The class JavaDoc states the explicit ordering rule:

SysUI application starts → SystemUIFactory is initialized → WMComponent is created → SysUIComponent is created (with WMComponents injected) → SysUI services are started → WMShell starts and binds SysUI with Shell components via exported Shell interfaces

In other words: the entire Shell graph is built and initialized before any SysUI CoreStartable runs. By the time WMShell.start() fires, every Shell feature is ready to receive callbacks. WMShell then subscribes to the SystemUI lifecycle controllers and forwards each change into the corresponding ShellInterface / per-feature method (e.g. KeyguardStateController → mShellInterface.onKeyguardVisibilityChanged(...), UserTracker → mShellInterface.onUserChanged(...)).

47.13.13 Key Source Files Reference (WM Shell)

File	Purpose
frameworks/base/libs/WindowManager/Shell/Android.bp	Module definitions, ProtoLog genrules, form-factor variants
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMComponent.java	Dagger subcomponent — Shell's public surface
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellBaseModule.java	Cross-form-factor base bindings (~1200 lines)
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java	Phone/tablet form-factor bindings
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/TvWMShellModule.java	TV form-factor bindings
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/sysui/ShellInterface.java	Lifecycle facade SysUI calls into
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/sysui/ShellController.java	Implementation of ShellInterface — event fan-out
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/sysui/ShellInit.java	Ordered init callback registry
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/ShellTaskOrganizer.java	Single TaskOrganizer registration; per-feature listeners
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/transition/Transitions.java	Transition handler registry and dispatch
frameworks/base/libs/WindowManager/Shell/src/com/android/wm/shell/protolog/ShellProtoLogGroup.java	ProtoLog group enum, transformed at build time
frameworks/base/packages/SystemUI/src/com/android/systemui/wmshell/WMShell.java	SysUI-side adapter CoreStartable
frameworks/base/libs/WindowManager/Jetpack/src/androidx/window/extensions/	Jetpack window extensions APK (separate from Shell)

---

47.14 Low-Light Dream Library

Sections 47.5 and (later) 47.15 mention the DREAMING keyguard state — the period where a DreamService (Android's screensaver mechanism, often called a daydream) is showing on top of the lock screen. The system dream is chosen by DreamManagerService, but on form factors that want to switch to a different dream in low ambient light — typically a dim, clock-only screensaver on a smart display, tablet, or Hub — the choice is mediated by a small library at frameworks/base/libs/dream/lowlight/, packaged as LowLightDreamLib and linked into SystemUI variants that need it.

This section walks through the library's surface, the state machine it implements, and how SystemUI's LowLightMonitor consumes it.

47.14.1 What the Library Owns and What It Does Not

LowLightDreamLib is intentionally narrow. It owns:

• The three-value ambient-light enum (AMBIENT_LIGHT_MODE_UNKNOWN, AMBIENT_LIGHT_MODE_REGULAR, AMBIENT_LIGHT_MODE_LOW_LIGHT).
• The "transition coordinator" that lets other SystemUI components run animations before the dream swap.
• The Dagger plumbing that lets a host SystemUI variant inject a ComponentName? for "the dream to show when it's dark".

It does not own:

• Ambient-light sensing. The host provides the sensor reading.
• The dream UI itself. The host (or an OEM-supplied APK) implements the DreamService whose ComponentName is wired through Dagger.
• The base "regular" dream. DreamManagerService chooses that from the per-user Settings.Secure.SCREENSAVER_COMPONENTS list — the library only overrides via setSystemDreamComponent.

Source layout (~5 source files, ~250 lines):

frameworks/base/libs/dream/lowlight/
  src/com/android/dream/lowlight/
    LowLightDreamManager.kt          -- core 3-mode state machine
    LowLightTransitionCoordinator.kt -- enter/exit animation hooks
    util/{KotlinUtils.kt, TruncatedInterpolator.kt}
    dagger/
      LowLightDreamModule.kt          -- @Provides for timeout, scope, dispatcher
      LowLightDreamComponent.kt       -- Subcomponent + Factory (host wires DreamManager + dream ComponentName)
      qualifiers/{Application.kt, Main.kt}
  res/values/config.xml               -- config_lowLightTransitionTimeoutMs (default 2000ms)

47.14.2 LowLightDreamManager: The 3-Mode State Machine

LowLightDreamManager is the only public class with side effects. Its state is a single @AmbientLightMode int plus an in-flight transition Job:

// Source: frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/
//   LowLightDreamManager.kt:42
class LowLightDreamManager @Inject constructor(
    @Application private val coroutineScope: CoroutineScope,
    private val dreamManager: DreamManager,
    private val lowLightTransitionCoordinator: LowLightTransitionCoordinator,
    @param:Named(LowLightDreamModule.LOW_LIGHT_DREAM_COMPONENT)
    private val lowLightDreamComponent: ComponentName?,
    @param:Named(LowLightDreamModule.LOW_LIGHT_TRANSITION_TIMEOUT_MS)
    private val lowLightTransitionTimeoutMs: Long
) {
    @RequiresPermission(Manifest.permission.WRITE_DREAM_STATE)
    fun setAmbientLightMode(@AmbientLightMode ambientLightMode: Int) {
        if (lowLightDreamComponent == null) {
            // ... log + bail. Host opted out of low-light dreams.
            return
        }
        if (mAmbientLightMode == ambientLightMode) return
        mAmbientLightMode = ambientLightMode
        val shouldEnterLowLight = mAmbientLightMode == AMBIENT_LIGHT_MODE_LOW_LIGHT

        mTransitionJob?.cancel()
        mTransitionJob = coroutineScope.launch {
            try {
                lowLightTransitionCoordinator.waitForLowLightTransitionAnimation(
                    timeout = mLowLightTransitionTimeout,
                    entering = shouldEnterLowLight
                )
            } catch (ex: TimeoutCancellationException) {
                Log.e(TAG, "timed out while waiting for low light animation", ex)
            } catch (ex: CancellationException) {
                Log.w(TAG, "low light transition animation cancelled")
                // Catch the cancellation so that we still set the system dream component if the
                // animation is cancelled, such as by a user tapping to wake as the transition to
                // low light happens.
            }
            dreamManager.setSystemDreamComponent(
                if (shouldEnterLowLight) lowLightDreamComponent else null
            )
        }
    }
}

Three details worth noting:

• lowLightDreamComponent == null is the opt-out. Hosts that do not want this feature bind the qualified ComponentName? to null. The manager then short-circuits every call without ever touching DreamManager. This is how the same SystemUI Dagger graph compiles across products that have a low-light dream and those that don't.
• One in-flight transition at a time. Each call cancels the previous mTransitionJob. If the ambient sensor oscillates around the threshold, you get at most one animation+setSystemDreamComponent per stable interval.
• The animation is awaited, not raced. The coroutineScope.launch blocks on the coordinator's waitForLowLightTransitionAnimation before swapping dreams. The swap happens after the host's enter/exit animator completes — so a SystemUI Compose animation runs first, then the dream cuts. The CancellationException branch deliberately falls through to still call setSystemDreamComponent, so a "wake while transitioning" still leaves the system in a coherent state instead of half-transitioned.

The WRITE_DREAM_STATE annotation reflects the underlying DreamManagerService permission: only the system UID and apps holding android.permission.WRITE_DREAM_STATE (a signature-or-system permission) can call this method, which matches the SystemUI process profile.

47.14.3 LowLightTransitionCoordinator: Letting the Host Animate First

A naked dream swap looks abrupt — the screen would cut from the regular dream (or the lock screen wallpaper) to the low-light dream with no fade. LowLightTransitionCoordinator lets the host register one enter listener and one exit listener, each of which returns an Animator?:

// Source: frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/
//   LowLightTransitionCoordinator.kt:30
@Singleton
class LowLightTransitionCoordinator @Inject constructor() {
    interface LowLightEnterListener {
        fun onBeforeEnterLowLight(): Animator?
    }
    interface LowLightExitListener {
        fun onBeforeExitLowLight(): Animator?
    }
    // ... setLowLightEnterListener(...) / setLowLightExitListener(...)

    suspend fun waitForLowLightTransitionAnimation(timeout: Duration, entering: Boolean) =
        suspendCoroutineWithTimeout(timeout) { continuation ->
            // ... call listener, listen on Animator.onAnimationEnd, resume continuation
        }
}

Two design choices stand out:

• One listener per direction. The coordinator deliberately does not support a list of subscribers. Stacking animations across multiple subsystems would race in ways the dream swap can't recover from. The host picks one orchestrator (usually a lowlightclock UI controller in the SystemUI variant that owns the low-light surface) and that orchestrator is responsible for fanning out internally.
• Returning null means "no animation, swap immediately." The helper resumes the continuation synchronously when the listener returns null, so a no-op host still gets the dream cut without an extra event-loop hop.

The 2000ms default timeout (config_lowLightTransitionTimeoutMs) is a floor: a stuck animation cannot block the dream forever, and setAmbientLightMode logs the timeout and proceeds with the swap.

47.14.4 Dagger Wiring on the Host Side

A SystemUI variant that wants the library injects a LowLightDreamComponent.Factory from its top-level component and provides the two values the library can't know: the system DreamManager and the dream ComponentName?.

// Source: frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/
//   dagger/LowLightDreamComponent.kt:25
@Subcomponent(modules = [LowLightDreamModule::class])
interface LowLightDreamComponent {
    @Subcomponent.Factory
    interface Factory {
        fun create(
            @BindsInstance dreamManager: DreamManager,
            @Named(LowLightDreamModule.LOW_LIGHT_DREAM_COMPONENT)
            @BindsInstance lowLightDreamComponent: ComponentName?
        ): LowLightDreamComponent
    }
}

LowLightDreamModule then provides the rest from Context resources:

// Source: frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/
//   dagger/LowLightDreamModule.kt:35
@Module
object LowLightDreamModule {
    @Provides @Named(LOW_LIGHT_TRANSITION_TIMEOUT_MS)
    fun providesLowLightTransitionTimeout(context: Context): Long =
        context.resources.getInteger(R.integer.config_lowLightTransitionTimeoutMs).toLong()

    @Provides @Main
    fun providesMainDispatcher(): CoroutineDispatcher = Dispatchers.Main.immediate

    @Provides @Application
    fun providesApplicationScope(@Main dispatcher: CoroutineDispatcher): CoroutineScope =
        CoroutineScope(dispatcher)
}

@Named(LOW_LIGHT_DREAM_COMPONENT) is the key seam. A product that defines a low-light dream points the binding at e.g. com.example.systemui/.LowLightDream; a product that does not want one binds null, and LowLightDreamManager.setAmbientLightMode becomes a no-op. The library compiles into every SystemUI flavour either way.

47.14.5 Consumption Path: SystemUI's LowLightMonitor

The consumer of the library in upstream AOSP is com.android.systemui.lowlightclock.LowLightMonitor. The monitor subscribes to whatever ambient-light source the SystemUI variant provides (vendor sensor service, light sensor, OEM cloud signal), maps that signal to one of the three enum values, and calls lowLightDreamManager.setAmbientLightMode(mode). The library handles the rest:

flowchart LR
    Sensor["Ambient light source<br/>(sensor / OEM service)"]
    Monitor["LowLightMonitor<br/>(SystemUI)"]
    Mgr["LowLightDreamManager<br/>(LowLightDreamLib)"]
    Coord["LowLightTransitionCoordinator"]
    HostUI["Host enter/exit listener<br/>(lowlightclock UI)"]
    DM["DreamManager<br/>(DreamManagerService)"]
    Dream["Low-light DreamService<br/>(per-product APK)"]

    Sensor --> Monitor
    Monitor --> Mgr
    Mgr --> Coord
    Coord --> HostUI
    HostUI --> Coord
    Mgr --> DM
    DM --> Dream

Note that the host UI sits behind the coordinator — the library calls the host, not the other way around. That keeps the SystemUI listener purely reactive (it never asks "is it dark?") and concentrates the state in the manager.

47.14.6 Where This Fits in the Wider Dream Story

The library is intentionally agnostic about what the low-light dream shows. In practice these are minimal, dim, mostly-static surfaces — common patterns are a low-brightness clock, an album-art screensaver, or a date/weather panel. The point of swapping at the DreamService level instead of inside one dream is composition: the regular dream can be a third-party screensaver picked by the user, while the low-light dream is a system-controlled, high-contrast, low-power-budget surface. The library is the bridge that lets a SystemUI variant flip between them without forcing every dream to implement its own dim mode.

For the broader screensaver / DreamService architecture (DreamManagerService, DreamOverlayService, doze + AOD interaction), see Chapter 47 §47.5 (Lock Screen) and §47.15 (Keyguard Deep Dive), which trace the DREAMING state through the keyguard state machine.

47.14.7 Key Source Files Reference (LowLightDreamLib)

File	Purpose
frameworks/base/libs/dream/lowlight/Android.bp	LowLightDreamLib android_library module, declares Dagger compiler plugin
frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/LowLightDreamManager.kt	3-mode state machine, calls DreamManager.setSystemDreamComponent
frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/LowLightTransitionCoordinator.kt	Enter/exit Animator? listener pair, coroutine await helper
frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/dagger/LowLightDreamModule.kt	@Provides for timeout, main dispatcher, application coroutine scope
frameworks/base/libs/dream/lowlight/src/com/android/dream/lowlight/dagger/LowLightDreamComponent.kt	Dagger @Subcomponent host wires DreamManager + ComponentName? into
frameworks/base/libs/dream/lowlight/res/values/config.xml	config_lowLightTransitionTimeoutMs (default 2000ms)
frameworks/base/packages/SystemUI/src/com/android/systemui/lowlightclock/LowLightMonitor.kt	SystemUI consumer that converts sensor signal to setAmbientLightMode

---

47.15 Keyguard Deep Dive

Section 47.5 introduced the lock screen architecture. This section explores the internal state machine, biometric unlock modes, bouncer flow, AOD transitions, and the MVI modernisation in much greater detail, drawing on the full keyguard source tree.

47.15.1 Keyguard State Machine

The keyguard subsystem is fundamentally a state machine. The KeyguardState enum defines all possible states:

// frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/
//   KeyguardState.kt
enum class KeyguardState {
    OFF,              // Display completely off, sensors disabled
    DOZING,           // Low-power mode, some sensors active
    DREAMING,         // Third-party dream (screensaver) showing
    AOD,              // Always-On Display showing minimal UI
    ALTERNATE_BOUNCER,// Biometric credential prompt (e.g. UDFPS)
    PRIMARY_BOUNCER,  // PIN / Pattern / Password prompt
    LOCKSCREEN,       // Full lock screen UI, device awake
    GLANCEABLE_HUB,   // Widget surface accessible from lock screen
    GONE,             // Keyguard dismissed, user in launcher/app
    UNDEFINED,        // Scene framework: any non-lockscreen scene
    OCCLUDED,         // Activity showing over keyguard
}

The full state transition graph:

stateDiagram-v2
    [*] --> OFF

    OFF --> DOZING : Screen off,<br/>sensors enabled
    OFF --> AOD : Screen off,<br/>AOD enabled

    DOZING --> AOD : AOD trigger
    DOZING --> LOCKSCREEN : Wake gesture<br/>lift/tap/power
    DOZING --> GONE : Fingerprint<br/>WAKE_AND_UNLOCK

    AOD --> LOCKSCREEN : Wake gesture
    AOD --> DOZING : AOD disabled
    AOD --> GONE : Fingerprint<br/>WAKE_AND_UNLOCK

    LOCKSCREEN --> PRIMARY_BOUNCER : Security challenge
    LOCKSCREEN --> ALTERNATE_BOUNCER : UDFPS prompt
    LOCKSCREEN --> AOD : Screen off timeout
    LOCKSCREEN --> DOZING : Screen off, no AOD
    LOCKSCREEN --> GONE : Swipe unlock<br/>no security
    LOCKSCREEN --> GLANCEABLE_HUB : Right edge swipe
    LOCKSCREEN --> OCCLUDED : showWhenLocked<br/>Activity
    LOCKSCREEN --> DREAMING : Dream starts

    PRIMARY_BOUNCER --> GONE : Correct credentials
    PRIMARY_BOUNCER --> LOCKSCREEN : Back / cancel

    ALTERNATE_BOUNCER --> GONE : Biometric match
    ALTERNATE_BOUNCER --> PRIMARY_BOUNCER : Fallback to PIN

    GLANCEABLE_HUB --> LOCKSCREEN : Left edge swipe
    GLANCEABLE_HUB --> PRIMARY_BOUNCER : Swipe up

    OCCLUDED --> LOCKSCREEN : Activity finishes
    OCCLUDED --> GONE : Unlock while occluded

    DREAMING --> LOCKSCREEN : Wake from dream
    DREAMING --> DOZING : Dream to doze

    GONE --> OFF : Screen off
    GONE --> DOZING : Screen off,<br/>sensors enabled
    GONE --> LOCKSCREEN : Lock timeout

States marked @Deprecated (PRIMARY_BOUNCER, GLANCEABLE_HUB, GONE, OCCLUDED) are being replaced by the Scene Container framework, which maps them to UNDEFINED and manages transitions through SceneTransitionLayout.

47.15.2 Awake vs Asleep State Classification

The KeyguardState companion object classifies each state for power management:

State	Awake	Asleep
OFF		X
DOZING		X
DREAMING		X
AOD		X
ALTERNATE_BOUNCER	X
PRIMARY_BOUNCER	X
LOCKSCREEN	X
GLANCEABLE_HUB	X
GONE	X
OCCLUDED	X
UNDEFINED	X

This classification drives the ThemeOverlayController deferred-colour logic (section 47.12.6) and various power-dependent behaviours.

47.15.3 KeyguardTransitionInteractor

KeyguardTransitionInteractor is the primary API for observing and driving transitions between keyguard states:

// frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/
//   KeyguardTransitionInteractor.kt
@SysUISingleton
class KeyguardTransitionInteractor @Inject constructor(
    @Application val scope: CoroutineScope,
    private val repository: KeyguardTransitionRepository,
    private val sceneInteractor: SceneInteractor,
    private val powerInteractor: PowerInteractor,
) {
    // Core observable:
    val transitionState: StateFlow<TransitionStep>

    // Per-state transition value (0.0 to 1.0):
    // Caches a MutableSharedFlow per KeyguardState for efficiency
    private val transitionValueCache = mutableMapOf<KeyguardState, MutableSharedFlow<Float>>()
}

Each TransitionStep contains:

• from: KeyguardState -- source state
• to: KeyguardState -- destination state
• value: Float -- progress from 0.0 (start) to 1.0 (complete)
• transitionState: TransitionState -- STARTED, RUNNING, CANCELED, FINISHED

Per-edge flows allow specific interactors to observe only the transitions they care about:

// Observe only LOCKSCREEN -> AOD transitions
keyguardTransitionInteractor.transition(Edge.create(from = LOCKSCREEN, to = AOD))
    .collect { step -> /* animate based on step.value */ }

47.15.4 Transition Interactor Hierarchy

Each state-to-state transition has a dedicated interactor:

FromAodTransitionInteractor
FromAlternateBouncerTransitionInteractor
FromDozingTransitionInteractor
FromDreamingTransitionInteractor
FromGlanceableHubTransitionInteractor
FromGoneTransitionInteractor
FromLockscreenTransitionInteractor
FromOccludedTransitionInteractor
FromPrimaryBouncerTransitionInteractor

These interactors listen for signals (power state changes, biometric events, user gestures) and call startTransition() on the repository to move the state machine forward. The StartKeyguardTransitionModule wires them all into Dagger.

47.15.5 KeyguardViewMediator Internals

KeyguardViewMediator (4,573 lines) remains the bridge between system_server and SystemUI's keyguard. Key internal mechanisms:

Lock Timeout Scheduling:

When the screen turns off, onStartedGoingToSleep() schedules a timeout via doKeyguardLocked(). The lock delay depends on:

• Settings.Secure.LOCK_SCREEN_LOCK_AFTER_TIMEOUT -- user-configured delay
• Trust agent state (Smart Lock may defer locking)
• Whether the device was locked manually (power button = immediate lock)

SIM PIN Management:

When the SIM requires a PIN, KeyguardViewMediator enters a special flow:

1. onSimStateChanged() detects SIM_LOCKED state
2. doKeyguardLocked() forces keyguard display regardless of other settings
3. The bouncer presents a SIM PIN input (distinct from the device PIN)
4. Upon successful verification, keyguard may dismiss or remain if device security is also pending

Occlusion Handling:

Activities declaring showWhenLocked=true can appear over the keyguard. The mediator tracks occlusion via setOccluded(boolean) and coordinates with StatusBarKeyguardViewManager to hide/show the underlying keyguard views.

47.15.6 Biometric Unlock Modes

The BiometricUnlockInteractor translates integer mode constants from BiometricUnlockController into the typed BiometricUnlockMode enum:

// frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/
//   BiometricUnlockModel.kt
enum class BiometricUnlockMode {
    NONE,                      // No biometric action
    WAKE_AND_UNLOCK,           // Fingerprint while screen off -> wake + dismiss
    WAKE_AND_UNLOCK_PULSING,   // Fingerprint during AOD pulse -> fade out + dismiss
    SHOW_BOUNCER,              // Biometric failure -> show PIN/pattern
    ONLY_WAKE,                 // Wake device, keyguard stays
    UNLOCK_COLLAPSING,         // Face/fingerprint while keyguard visible
    DISMISS_BOUNCER,           // Biometric while bouncer visible -> dismiss
    WAKE_AND_UNLOCK_FROM_DREAM // Fingerprint while dreaming -> wake + dismiss
}

The mode determines the keyguard state transition:

graph TD
    FP["Fingerprint<br/>Acquired"]
    FACE["Face<br/>Acquired"]

    FP --> |"Screen OFF"| WAU["WAKE_AND_UNLOCK<br/>OFF/DOZING -> GONE"]
    FP --> |"AOD Pulsing"| WAUP["WAKE_AND_UNLOCK_PULSING<br/>AOD -> GONE"]
    FP --> |"Screen ON,<br/>Keyguard visible"| UC["UNLOCK_COLLAPSING<br/>LOCKSCREEN -> GONE"]
    FP --> |"Dreaming"| WAUD["WAKE_AND_UNLOCK_FROM_DREAM<br/>DREAMING -> GONE"]
    FP --> |"Bouncer visible"| DB["DISMISS_BOUNCER<br/>PRIMARY_BOUNCER -> GONE"]

    FACE --> |"Bypass enabled"| UC
    FACE --> |"Bypass disabled,<br/>on lockscreen"| OW["ONLY_WAKE<br/>Stay on LOCKSCREEN"]
    FACE --> |"Bouncer visible"| DB
    FACE --> |"Failed"| SB["SHOW_BOUNCER<br/>LOCKSCREEN -> PRIMARY_BOUNCER"]

The BiometricUnlockModel pairs the mode with a BiometricUnlockSource (FINGERPRINT_SENSOR, FACE_SENSOR, etc.) for audit and animation purposes.

47.15.7 Bouncer Flow Detail

The bouncer subsystem uses the MVI pattern with a clear data/domain/UI separation:

frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/
  data/repository/
    BouncerRepositoryModule.kt        -- Dagger bindings
    KeyguardBouncerRepository.kt      -- State repository
  domain/interactor/
    BouncerInteractor.kt              -- Main interactor
    PrimaryBouncerInteractor.kt       -- PIN/pattern/password
    AlternateBouncerInteractor.kt     -- UDFPS/biometric
  domain/startable/
    BouncerStartable.kt               -- CoreStartable wiring
  ui/
    BouncerView.kt                    -- Compose UI

Primary Bouncer Lifecycle:

sequenceDiagram
    participant User
    participant KTI as KeyguardTransitionInteractor
    participant PBI as PrimaryBouncerInteractor
    participant KBR as KeyguardBouncerRepository
    participant BV as BouncerView
    participant LPU as LockPatternUtils

    User->>KTI: Swipe up on lockscreen
    KTI->>KTI: startTransition(LOCKSCREEN -> PRIMARY_BOUNCER)
    KTI->>PBI: Transition triggers bouncer show
    PBI->>KBR: setPrimaryShow(true)
    KBR-->>BV: primaryBouncerShow flow emits true
    BV->>BV: Inflate PIN/Pattern/Password input

    User->>BV: Enter PIN "1234"
    BV->>PBI: onAuthenticate(pin)
    PBI->>LPU: checkCredential(pin, userId)

    alt Correct
        LPU-->>PBI: Success
        PBI->>KBR: setPrimaryShow(false)
        PBI->>KTI: startTransition(PRIMARY_BOUNCER -> GONE)
    else Wrong
        LPU-->>PBI: Failure
        PBI->>BV: showError("Wrong PIN")
        Note over BV: Lockout after N failures
    end

Alternate Bouncer (UDFPS):

When the device has an under-display fingerprint sensor, the alternate bouncer presents a fingerprint icon overlay:

1. AlternateBouncerInteractor detects the device supports UDFPS
2. On lockscreen wake, it triggers LOCKSCREEN -> ALTERNATE_BOUNCER
3. The UDFPS overlay shows a fingerprint icon at the sensor location
4. If the user taps the sensor and fingerprint matches -> GONE
5. If the user wants PIN instead -> ALTERNATE_BOUNCER -> PRIMARY_BOUNCER

47.15.8 AOD Transition Pipeline

The Always-On Display transition involves multiple coordinated subsystems:

sequenceDiagram
    participant PM as PowerManager
    participant KVM as KeyguardViewMediator
    participant DSH as DozeServiceHost
    participant DSC as DozeScrimController
    participant KTI as KeyguardTransitionInteractor
    participant FADE as FromAodTransitionInteractor

    PM->>KVM: onStartedGoingToSleep()
    KVM->>KTI: startTransition(LOCKSCREEN -> AOD)
    KTI-->>DSC: transitionValue(AOD): 0.0 -> 1.0
    DSC->>DSC: Animate scrim alpha

    Note over DSH: Doze service starts
    DSH->>DSH: Set pulse parameters

    PM->>KVM: onFinishedGoingToSleep()
    Note over DSC: AOD UI fully visible

    Note over DSH: Notification arrives
    DSH->>KTI: startTransition(AOD -> LOCKSCREEN)
    KTI-->>FADE: FromAodTransitionInteractor triggers
    FADE->>DSC: Animate scrim to transparent
    FADE->>DSC: Wake screen

Doze parameters control AOD behaviour:

• DozeParameters.getAlwaysOn() -- whether AOD is enabled
• DozeParameters.shouldControlScreenOff() -- animation vs immediate off
• DozeParameters.getPulseVisibleDuration() -- how long notification pulse shows

47.15.9 KeyguardRepository -- The Data Layer

The KeyguardRepository interface centralises all keyguard state:

frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/data/repository/
  KeyguardRepository.kt               -- Core keyguard state
  BiometricSettingsRepository.kt       -- Biometric configuration
  DevicePostureRepository.kt           -- Fold state
  KeyguardBypassRepository.kt          -- Face bypass settings
  KeyguardClockRepository.kt           -- Clock face selection
  KeyguardOcclusionRepository.kt       -- Activity occlusion
  KeyguardQuickAffordanceRepository.kt -- Bottom shortcuts
  KeyguardSmartspaceRepository.kt      -- Smart suggestions
  KeyguardSurfaceBehindRepository.kt   -- Behind-keyguard surface
  InWindowLauncherUnlockAnimationRepository.kt -- Unlock animation

Key flows exposed by KeyguardRepository:

• isKeyguardShowing: StateFlow<Boolean>
• isKeyguardOccluded: StateFlow<Boolean>
• biometricUnlockState: StateFlow<BiometricUnlockModel>
• isDozing: StateFlow<Boolean>
• isDreaming: StateFlow<Boolean>
• wakefulness: StateFlow<WakefulnessModel>

47.15.10 Scene Container Migration

The keyguard is undergoing a major migration to the Scene Container architecture. Under this model:

graph TB
    subgraph "Legacy (being replaced)"
        KVM_L["KeyguardViewMediator<br/>manages show/hide"]
        SBKVM_L["StatusBarKeyguardViewManager<br/>bridges to views"]
        CS_L["CentralSurfacesImpl<br/>owns the window"]
    end

    subgraph "Scene Container (new)"
        STL["SceneTransitionLayout<br/>Compose-based scene manager"]
        LS["Lockscreen Scene"]
        BS["Bouncer Overlay"]
        GS["Gone Scene"]
        OS["Occluded Scene"]
        CHS["Communal Scene"]
    end

    KVM_L -.->|"migrating to"| STL
    SBKVM_L -.->|"migrating to"| LS
    CS_L -.->|"migrating to"| STL

KeyguardState.mapToSceneContainerContent() maps legacy states to scene keys:

• LOCKSCREEN, AOD, DOZING, DREAMING, OFF, ALTERNATE_BOUNCER all map to Scenes.Lockscreen
• PRIMARY_BOUNCER maps to Overlays.Bouncer
• GONE maps to Scenes.Gone
• OCCLUDED maps to Scenes.Occluded
• GLANCEABLE_HUB maps to Scenes.Communal

The SceneContainerFlag controls whether the new path is active, with @Deprecated annotations on states that will not exist post-migration.

47.15.11 Key Source Paths (Keyguard)

Path	Description
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardViewMediator.java	4,573-line mediator
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardService.java	system_server bridge
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardLifecyclesDispatcher.java	Lifecycle events
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardUnlockAnimationController.kt	Unlock animation
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/KeyguardState.kt	State enum (11 states)
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/BiometricUnlockModel.kt	Unlock mode enum (8 modes)
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/TransitionStep.kt	Transition progress
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/TransitionState.kt	Transition state (STARTED/RUNNING/CANCELED/FINISHED)
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/DozeStateModel.kt	Doze states
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/shared/model/DozeTransitionModel.kt	Doze transitions
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/data/repository/KeyguardRepository.kt	Core state repository
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/data/repository/KeyguardTransitionRepository.kt	Transition state repository
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/data/repository/BiometricSettingsRepository.kt	Biometric config repository
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/data/repository/KeyguardOcclusionRepository.kt	Occlusion tracking repository
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/KeyguardInteractor.kt	General keyguard interactor
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/KeyguardTransitionInteractor.kt	Transition observation
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/BiometricUnlockInteractor.kt	Biometric mode mapping
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/KeyguardDismissInteractor.kt	Dismiss handling
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/KeyguardEnabledInteractor.kt	Enable/disable
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/From*TransitionInteractor.kt	Per-state transition drivers
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/TrustInteractor.kt	Smart Lock interactor
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/domain/interactor/DozeInteractor.kt	Doze management
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/ui/KeyguardViewConfigurator.kt	View setup
frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/data/repository/KeyguardBouncerRepository.kt	Bouncer repository
frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/domain/interactor/PrimaryBouncerInteractor.kt	Primary bouncer interactor
frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/domain/interactor/AlternateBouncerInteractor.kt	Alternate bouncer interactor
frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/ui/BouncerView.kt	Bouncer view

---

47.16 Try It: Add a Custom QS Tile

This hands-on exercise demonstrates how to add a new built-in Quick Settings tile to SystemUI. We will create a "Caffeine" tile that keeps the screen awake.

47.16.1 Step 1: Create the Tile Class

Create a new file in the tiles directory:

frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tiles/
  CaffeineTile.java

package com.android.systemui.qs.tiles;

import android.content.Intent;
import android.os.Handler;
import android.os.Looper;
import android.os.PowerManager;
import android.service.quicksettings.Tile;

import androidx.annotation.Nullable;

import com.android.internal.logging.MetricsLogger;
import com.android.systemui.animation.Expandable;
import com.android.systemui.dagger.qualifiers.Background;
import com.android.systemui.dagger.qualifiers.Main;
import com.android.systemui.plugins.ActivityStarter;
import com.android.systemui.plugins.FalsingManager;
import com.android.systemui.plugins.qs.QSTile.BooleanState;
import com.android.systemui.plugins.statusbar.StatusBarStateController;
import com.android.systemui.qs.QSHost;
import com.android.systemui.qs.QsEventLogger;
import com.android.systemui.qs.logging.QSLogger;
import com.android.systemui.qs.tileimpl.QSTileImpl;
import com.android.systemui.res.R;

import javax.inject.Inject;

/**
 * Quick settings tile: Caffeine (keep screen awake).
 *
 * This tile acquires a partial wake lock to prevent the screen from
 * turning off.  The wake lock is released when the tile is toggled
 * off or when SystemUI is destroyed.
 */
public class CaffeineTile extends QSTileImpl<BooleanState> {

    public static final String TILE_SPEC = "caffeine";

    private final PowerManager.WakeLock mWakeLock;
    private boolean mIsActive = false;

    @Inject
    public CaffeineTile(
            QSHost host,
            QsEventLogger uiEventLogger,
            @Background Looper backgroundLooper,
            @Main Handler mainHandler,
            FalsingManager falsingManager,
            MetricsLogger metricsLogger,
            StatusBarStateController statusBarStateController,
            ActivityStarter activityStarter,
            QSLogger qsLogger,
            PowerManager powerManager) {
        super(host, uiEventLogger, backgroundLooper, mainHandler,
                falsingManager, metricsLogger, statusBarStateController,
                activityStarter, qsLogger);
        mWakeLock = powerManager.newWakeLock(
                PowerManager.FULL_WAKE_LOCK, "SystemUI:CaffeineTile");
    }

    @Override
    public BooleanState newTileState() {
        BooleanState state = new BooleanState();
        state.handlesLongClick = false;
        return state;
    }

    @Override
    protected void handleClick(@Nullable Expandable expandable) {
        mIsActive = !mIsActive;
        if (mIsActive) {
            mWakeLock.acquire();
        } else {
            if (mWakeLock.isHeld()) {
                mWakeLock.release();
            }
        }
        refreshState();
    }

    @Override
    protected void handleUpdateState(BooleanState state, Object arg) {
        state.value = mIsActive;
        state.state = mIsActive ? Tile.STATE_ACTIVE : Tile.STATE_INACTIVE;
        state.label = "Caffeine";
        state.contentDescription = "Keep screen awake";
        // Use an appropriate icon resource:
        state.icon = ResourceIcon.get(mIsActive
                ? R.drawable.ic_caffeine_on   // You must add these drawables
                : R.drawable.ic_caffeine_off);
    }

    @Override
    public int getMetricsCategory() {
        return 0; // Custom category or use MetricsEvent.QS_CUSTOM
    }

    @Override
    public Intent getLongClickIntent() {
        return new Intent(android.provider.Settings.ACTION_DISPLAY_SETTINGS);
    }

    @Override
    public CharSequence getTileLabel() {
        return "Caffeine";
    }

    @Override
    protected void handleDestroy() {
        super.handleDestroy();
        if (mWakeLock.isHeld()) {
            mWakeLock.release();
        }
    }
}

47.16.2 Step 2: Register the Tile in the QS Factory

The tile must be registered so QSHost can create it from its tile spec. Find the tile creation factory (typically in the QS Dagger module or QSFactoryImpl) and add a case for "caffeine":

// In the factory that maps tile specs to tile instances:
case CaffeineTile.TILE_SPEC:
    return mCaffeineTileProvider.get();

You also need to add the Dagger provider. In the relevant Dagger module:

@Binds
@IntoMap
@StringKey(CaffeineTile.TILE_SPEC)
abstract QSTile bindCaffeineTile(CaffeineTile tile);

47.16.3 Step 3: Add Drawable Resources

Add icon resources to the SystemUI res/ directory:

frameworks/base/packages/SystemUI/res/drawable/
  ic_caffeine_on.xml    -- Filled coffee cup icon (active state)
  ic_caffeine_off.xml   -- Outlined coffee cup icon (inactive state)

For vector drawables, use 24x24dp with the appropriate tint.

47.16.4 Step 4: Add to Default Tile List (Optional)

To include the tile in the default QS panel, modify the string resource:

<!-- frameworks/base/packages/SystemUI/res/values/config.xml -->
<string name="quick_settings_tiles_default" translatable="false">
    wifi,cell,battery,flashlight,rotation,caffeine
</string>

47.16.5 Step 5: Build and Test

# Build SystemUI
m SystemUI

# Push to device
adb root
adb remount
adb sync system
adb shell stop
adb shell start

# Or for faster iteration, restart just SystemUI:
adb shell killall com.android.systemui

Verify the tile appears in the QS editor. If not in the default list, open the QS edit mode (pencil icon) and drag the "Caffeine" tile into the active area.

47.16.6 Step 6: Verify Functionality

# Check wake lock state
adb shell dumpsys power | grep -i "wake lock"

# Toggle the tile and verify the wake lock appears/disappears
# Look for: "SystemUI:CaffeineTile" in the output

47.16.7 Architecture Summary of a QS Tile

graph TD
    subgraph "Your Tile"
        CT["CaffeineTile"]
        CT -->|"extends"| QTI["QSTileImpl<BooleanState>"]
        QTI -->|"implements"| QST["QSTile (plugin interface)"]
    end
    subgraph "QS Framework"
        QSH["QSHost"]
        QSF["QSFactory"]
        QSP["QSPanel"]
        QTV["QSTileView"]
    end
    subgraph "Dagger"
        MOD["Dagger Module<br/>@IntoMap @StringKey"]
    end
    MOD -->|"provides"| CT
    QSH -->|"creates via"| QSF
    QSF -->|"instantiates"| CT
    CT -->|"state updates"| QTV
    QTV -->|"displayed in"| QSP

47.16.8 Testing the Tile

For unit testing, follow the existing pattern in the SystemUI test directory:

frameworks/base/packages/SystemUI/multivalentTests/

Create a test class that:

1. Mocks PowerManager and PowerManager.WakeLock
2. Calls handleClick() and verifies wake lock acquisition
3. Calls handleClick() again and verifies wake lock release
4. Calls handleDestroy() and verifies cleanup

@SmallTest
@RunWith(AndroidTestingRunner.class)
public class CaffeineTileTest extends SysuiTestCase {
    private CaffeineTile mTile;
    @Mock private PowerManager mPowerManager;
    @Mock private PowerManager.WakeLock mWakeLock;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
        when(mPowerManager.newWakeLock(anyInt(), anyString()))
                .thenReturn(mWakeLock);
        // Create tile with mocked dependencies
    }

    @Test
    public void testClick_acquiresWakeLock() {
        mTile.handleClick(null);
        verify(mWakeLock).acquire();
    }

    @Test
    public void testDoubleClick_releasesWakeLock() {
        when(mWakeLock.isHeld()).thenReturn(true);
        mTile.handleClick(null);  // ON
        mTile.handleClick(null);  // OFF
        verify(mWakeLock).release();
    }

    @Test
    public void testDestroy_releasesWakeLock() {
        when(mWakeLock.isHeld()).thenReturn(true);
        mTile.handleClick(null);  // ON
        mTile.handleDestroy();
        verify(mWakeLock).release();
    }
}

---

Summary

SystemUI is a massive, continuously evolving codebase that implements nearly every system-level UI surface on Android. This chapter covered:

Section	Key Classes	Lines of Code (approx.)
Architecture	SystemUIApplicationImpl, GlobalRootComponent, SysUIComponent, CoreStartable	~500
Status Bar	CentralSurfacesImpl, StatusBarWindowControllerImpl, CollapsedStatusBarFragment	~3,300
Notification Shade	NotificationPanelViewController, ShadeController, NotificationStackScrollLayout	~4,300
Quick Settings	QSHost, QSTileImpl, QSPanel, CustomTile	~2,000
Lock Screen	KeyguardViewMediator, StatusBarKeyguardViewManager, Bouncer	~4,600
Recent Apps	OverviewProxyRecentsImpl, LauncherProxyService	~110
Volume Dialog	VolumeDialogControllerImpl, VolumeDialogImpl	~2,900
Power Menu	GlobalActionsComponent, GlobalActionsDialogLite	~3,100
Screenshots	ScreenshotController, ImageCapture, ImageExporter	~1,200
Multi-Display	PerDisplayRepository, StatusBarWindowControllerStore	~300
Navigation Bar	NavigationBarView, EdgeBackGestureHandler, NavigationModeController	~2,500
Monet / Dynamic Color	ThemeOverlayController, ColorScheme, TonalPalette, DynamicColors	~1,600
Keyguard Deep Dive	KeyguardState, KeyguardTransitionInteractor, BiometricUnlockInteractor	~4,600

The codebase is transitioning from monolithic controllers to an MVI architecture with Dagger DI, Kotlin coroutines, and Jetpack Compose. Key modernisation efforts include:

• Scene Container -- replacing CentralSurfaces with a scene-based architecture
• QS Compose -- rewriting Quick Settings in Jetpack Compose
• ShadeWindowGoesAround -- per-display shade windows
• Predictive Back -- back gesture with animation preview
• StatusBarConnectedDisplays -- status bar on external displays

Key Source Paths

Path	Description
frameworks/base/packages/SystemUI/AndroidManifest.xml	Process declaration
frameworks/base/packages/SystemUI/src/com/android/systemui/application/impl/SystemUIApplicationImpl.java	App startup
frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIService.java	Entry service
frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIInitializer.java	Dagger initialisation
frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/GlobalRootComponent.java	Root DI component
frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/SysUIComponent.java	Main DI subcomponent
frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/SystemUICoreStartableModule.kt	Startable bindings
frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/SystemUIModule.java	Module aggregator
frameworks/base/packages/SystemUI/src/com/android/systemui/dagger/PerDisplayRepositoriesModule.kt	Multi-display DI
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/CentralSurfaces.java	Status bar interface
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/CentralSurfacesImpl.java	Status bar implementation
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBarKeyguardViewManager.java	Keyguard bridge
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/window/StatusBarWindowControllerImpl.java	Status bar window
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/fragment/CollapsedStatusBarFragment.java	Status bar content
frameworks/base/packages/SystemUI/src/com/android/systemui/shade/NotificationPanelViewController.java	Shade panel
frameworks/base/packages/SystemUI/src/com/android/systemui/shade/ShadeController.java	Shade abstraction
frameworks/base/packages/SystemUI/src/com/android/systemui/shade/NotificationShadeWindowControllerImpl.java	Shade window
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/QSHost.java	QS tile management
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/QSPanel.java	QS tile grid
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tileimpl/QSTileImpl.java	Base tile
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/tiles/	Built-in tiles
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/external/CustomTile.java	Third-party tiles
frameworks/base/packages/SystemUI/src/com/android/systemui/qs/pipeline/	New tile pipeline
frameworks/base/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardViewMediator.java	Lock screen logic
frameworks/base/packages/SystemUI/src/com/android/systemui/bouncer/	Bouncer (security challenge, MVI)
frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/NavigationBarControllerImpl.java	Nav bar controller
frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/NavigationModeController.java	Nav bar mode tracking
frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/views/NavigationBarView.java	Nav bar view
frameworks/base/packages/SystemUI/src/com/android/systemui/navigationbar/gestural/EdgeBackGestureHandler.java	Gesture navigation
frameworks/base/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogControllerImpl.java	Volume state
frameworks/base/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogImpl.java	Volume UI
frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/GlobalActionsComponent.java	Power menu entry
frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/GlobalActionsImpl.java	Power menu default impl
frameworks/base/packages/SystemUI/src/com/android/systemui/globalactions/GlobalActionsDialogLite.java	Power menu dialog UI
frameworks/base/packages/SystemUI/src/com/android/systemui/screenshot/ScreenshotController.kt	Screenshot flow
frameworks/base/packages/SystemUI/src/com/android/systemui/screenshot/TakeScreenshotService.java	Screenshot service
frameworks/base/packages/SystemUI/src/com/android/systemui/recents/OverviewProxyRecentsImpl.java	Recents proxy
frameworks/base/packages/SystemUI/src/com/android/systemui/display/dagger/SystemUIDisplaySubcomponent.java	Display-scoped DI
frameworks/base/packages/SystemUI/plugin/src/com/android/systemui/plugins/qs/QSTile.java	Tile plugin interface
frameworks/base/packages/SystemUI/plugin/src/com/android/systemui/plugins/GlobalActions.java	Power menu plugin
frameworks/base/packages/SystemUI/plugin/src/com/android/systemui/plugins/VolumeDialogController.java	Volume plugin