In the spirit of writing stuff down
Write some stuff down Test: none Change-Id: I9997db5f9c4d75b0c066f002f234dbeaec6932a4
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Jason Monk
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# SystemUI Documentation
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# SystemUI
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“Everything you see in Android that's not an app”
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SystemUI is a persistent process that provides UI for the system but outside
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of the system_server process.
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The starting point for most of sysui code is a list of services that extend
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SystemUI that are started up by SystemUIApplication. These services then depend
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on some custom dependency injection provided by Dependency.
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Inputs directed at sysui (as opposed to general listeners) generally come in
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through IStatusBar. Outputs from sysui are through a variety of private APIs to
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the android platform all over.
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## SystemUIApplication
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When SystemUIApplication starts up, it will start up the services listed in
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config_systemUIServiceComponents or config_systemUIServiceComponentsPerUser.
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Each of these services extend SystemUI. SystemUI provides them with a Context
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and gives them callbacks for onConfigurationChanged (this historically was
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the main path for onConfigurationChanged, now also happens through
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ConfigurationController). They also receive a callback for onBootCompleted
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since these objects may be started before the device has finished booting.
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SystemUI and SystemUIApplication also have methods for putComponent and
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getComponent which were existing systems to get a hold of other parts of
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sysui before Dependency existed. Generally new things should not be added
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to putComponent, instead Dependency and other refactoring is preferred to
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make sysui structure cleaner.
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Each SystemUI service is expected to be a major part of system ui and the
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goal is to minimize communication between them. So in general they should be
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relatively silo'd.
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## Dependencies
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The first SystemUI service that is started should always be Dependency.
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Dependency provides a static method for getting a hold of dependencies that
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have a lifecycle that spans sysui. Dependency has code for how to create all
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dependencies manually added. SystemUIFactory is also capable of
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adding/replacing these dependencies.
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Dependencies are lazily initialized, so if a Dependency is never referenced at
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runtime, it will never be created.
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If an instantiated dependency implements Dumpable it will be included in dumps
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of sysui (and bug reports), allowing it to include current state information.
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This is how \*Controllers dump state to bug reports.
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If an instantiated dependency implements ConfigurationChangeReceiver it will
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receive onConfigurationChange callbacks when the configuration changes.
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## IStatusBar
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CommandQueue is the object that receives all of the incoming events from the
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system_server. It extends IStatusBar and dispatches those callbacks back any
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number of listeners. The system_server gets a hold of the IStatusBar when
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StatusBar calls IStatusBarService#registerStatusBar, so if StatusBar is not
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included in the XML service list, it will not be registered with the OS.
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CommandQueue posts all incoming callbacks to a handler and then dispatches
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those messages to each callback that is currently registered. CommandQueue
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also tracks the current value of disable flags and will call #disable
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immediately for any callbacks added.
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There are a few places where CommandQueue is used as a bus to communicate
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across sysui. Such as when StatusBar calls CommandQueue#recomputeDisableFlags.
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This is generally used a shortcut to directly trigger CommandQueue rather than
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calling StatusManager and waiting for the call to come back to IStatusBar.
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## Default SystemUI services list
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### [com.android.systemui.Dependency](/packages/SystemUI/src/com/android/systemui/Dependency.java)
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Provides custom dependency injection.
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### [com.android.systemui.util.NotificationChannels](/packages/SystemUI/src/com/android/systemui/util/NotificationChannels.java)
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Creates/initializes the channels sysui uses when posting notifications.
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### [com.android.systemui.statusbar.CommandQueue$CommandQueueStart](/packages/SystemUI/src/com/android/systemui/sstatusbar/CommandQueue.java)
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Creates CommandQueue and calls putComponent because its always been there
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and sysui expects it to be there :/
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### [com.android.systemui.keyguard.KeyguardViewMediator](/packages/SystemUI/src/com/android/systemui/keyguard/KeyguardViewMediator.java)
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Manages keyguard view state.
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### [com.android.systemui.recents.Recents](/packages/SystemUI/src/com/android/systemui/recents/Recents.java)
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Recents tracks all the data needed for recents and starts/stops the recents
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activity. It provides this cached data to RecentsActivity when it is started.
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### [com.android.systemui.volume.VolumeUI](/packages/SystemUI/src/com/android/systemui/volume/VolumeUI.java)
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Registers all the callbacks/listeners required to show the Volume dialog when
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it should be shown.
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### [com.android.systemui.stackdivider.Divider](/packages/SystemUI/src/com/android/systemui/stackdivider/Divider.java)
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Shows the drag handle for the divider between two apps when in split screen
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mode.
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### [com.android.systemui.SystemBars](/packages/SystemUI/src/com/android/systemui/SystemBars.java)
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This is a proxy to the actual SystemUI for the status bar. This loads from
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config_statusBarComponent which defaults to StatusBar. (maybe this should be
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removed and copy how config_systemUiVendorServiceComponent works)
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### [com.android.systemui.status.phone.StatusBar](/packages/SystemUI/src/com/android/systemui/status/phone/StatusBar.java)
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This shows the UI for the status bar and the notification shade it contains.
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It also contains a significant amount of other UI that interacts with these
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surfaces (keyguard, AOD, etc.). StatusBar also contains a notification listener
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to receive notification callbacks.
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### [com.android.systemui.usb.StorageNotification](/packages/SystemUI/src/com/android/systemui/usb/StorageNotification.java)
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Tracks USB status and sends notifications for it.
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### [com.android.systemui.power.PowerUI](/packages/SystemUI/src/com/android/systemui/power/PowerUI.java)
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Tracks power status and sends notifications for low battery/power saver.
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### [com.android.systemui.media.RingtonePlayer](/packages/SystemUI/src/com/android/systemui/media/RingtonePlayer.java)
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Plays ringtones.
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### [com.android.systemui.keyboard.KeyboardUI](/packages/SystemUI/src/com/android/systemui/keyboard/KeyboardUI.java)
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Shows UI for keyboard shortcuts (triggered by keyboard shortcut).
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### [com.android.systemui.pip.PipUI](/packages/SystemUI/src/com/android/systemui/pip/PipUI.java)
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Shows the overlay controls when Pip is showing.
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### [com.android.systemui.shortcut.ShortcutKeyDispatcher](/packages/SystemUI/src/com/android/systemui/shortcut/ShortcutKeyDispatcher.java)
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Dispatches shortcut to System UI components.
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### @string/config_systemUIVendorServiceComponent
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Component allowing the vendor/OEM to inject a custom component.
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### [com.android.systemui.util.leak.GarbageMonitor$Service](/packages/SystemUI/src/com/android/systemui/util/leak/GarbageMonitor.java)
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Tracks large objects in sysui to see if there are leaks.
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### [com.android.systemui.LatencyTester](/packages/SystemUI/src/com/android/systemui/LatencyTester.java)
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Class that only runs on debuggable builds that listens to broadcasts that
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simulate actions in the system that are used for testing the latency.
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### [com.android.systemui.globalactions.GlobalActionsComponent](/packages/SystemUI/src/com/android/systemui/globalactions/GlobalActionsComponent.java)
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Shows the global actions dialog (long-press power).
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### [com.android.systemui.ScreenDecorations](/packages/SystemUI/src/com/android/systemui/ScreenDecorations.java)
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Draws decorations about the screen in software (e.g. rounded corners, cutouts).
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### [com.android.systemui.fingerprint.FingerprintDialogImpl](/packages/SystemUI/src/com/android/systemui/fingerprint/FingerprintDialogImpl.java)
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Fingerprint UI.
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---
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