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diff --git a/packages/SystemUI/docs/media-controls.md b/packages/SystemUI/docs/media-controls.md new file mode 100644 index 000000000000..579f453a3a92 --- /dev/null +++ b/packages/SystemUI/docs/media-controls.md @@ -0,0 +1,94 @@ +# SysUI Media Controls Pipeline + +[TOC] + +## Purpose + +Describe how events flow through the media controls pipeline, and provide a high level overview of what the different components do. + +## Pipeline Diagram + + + +* Orange: External inputs +* Blue: Internal listeners; all except `MediaDataManager` and `ResumeMediaBrowser` implement [`MediaDataManager.Listener`](/packages/SystemUI/src/com/android/systemui/media/MediaDataManager.kt#711) and receive `onMediaDataLoaded` and `onMediaDataRemoved` events + +## Classes + +Files under [`systemui/media/`](/packages/SystemUI/src/com/android/systemui/media/): + +* UI + * `dialog/` + * Output switcher dialog (maintained by Settings team) + * IlluminationDrawable.kt + * LightSourceDrawable.kt + * These create the glow animation when you tap on a button (see [`qs_media_light_source`](/packages/SystemUI/res/drawable/qs_media_light_source.xml)). Should be reusable in other layouts. + * Carousel: + * MediaCarouselController.kt + * Keeps the carousel view up to date and handles state changes (e.g. expansion) + * Handles settings gear and page indicator + * MediaCarouselScrollHandler.kt + * Handles scrolling between players in the carousel + * MediaScrollView.kt + * Scrollview used in the carousel layout, has some custom measurement code + * Individual players: + * KeyguardMediaController.kt + * Lockscreen media controls have a special wrapper in order to work with the existing lockscreen notification layout + * MediaControlPanel.java + * Main class for media control UI + * SeekBarObserver.kt + * Updates seekbar state + * SeekBarViewModel.kt + * Implements its own `computePosition()` for the seekbar (to avoid continually polling the `PlaybackState`, which involves binder calls) + * Does some touch falsing (ignore flings, require drags to start near the thumb - otherwise users would often accidentally trigger the seekbar when they meant to move the carousel or shade) + * PlayerViewHolder.kt + * Holds references to the UI elements in the panel +* Animation support: + * MediaHierarchyManager.kt + * Responsible for placement of media view and animation between hosts + * MediaHost.kt + * Every location that a media player could be located needs a `MediaHost` + * Tracks configuration (if it should show inactive media, needs falsing, etc.) + * MediaHostStatesManager.kt + * Manages the various media host states and coordinates heights between different players + * Has the most up to date state for any location + * MediaViewController.kt + * Controls a single instance of a media player, keeps the media view states up to date +* Backend + * MediaData.kt + * Holds all the media data (track info, active/resume state, etc.) + * MediaDataCombineLatest.kt + * Combines update events from `MediaDataManager` and `MediaDeviceManager`, so that downstream listeners will have device info + * MediaDataFilter.kt + * Filters media data based on the current user + * Exit point for the pipeline: "external listeners" (currently `MediaHost` and `MediaCarouselController`), while they should be added via `MediaDataManager.addListener()`, will actually be listening to this output + * MediaDataManager.kt + * Entry point for the pipeline; initializes listener connections and assigns external listeners to the correct exit point + * Converts media notifications and resumable media info into `MediaData` + * MediaDeviceManager.kt + * Handles device updates + * MediaFeatureFlag.kt + * Utility to check whether media controls are enabled + * MediaSessionBasedFilter.kt + * Filters media events based on media session. This prevents duplicate controls in situations like casting where we might get both a local and remote object for the same media session. + * MediaTimeoutListener.kt + * Listens to `PlaybackState` and marks controls inactive after the media has been paused/stopped for 10 minutes (value can be adjusted locally with `adb shell setprop debug.sysui.media_timeout [ms]`) + * MediaResumeListener.kt + * Listens for new media data and attempts to find a valid `MediaBrowserService` for the app. If successful, sends the information back to the `MediaDataManager` + * Saves up to 5 valid `MediaBrowserService` components found this way, and queries them for recent media on boot or user change + * Note: the user can disable this feature completely (or block certain apps from being resumable) in [Settings](https://source.corp.google.com/android/packages/apps/Settings/src/com/android/settings/sound/ResumableMediaAppsController.java), in which case this listener will do nothing (or ignore updates from the blocked apps). + * ResumeMediaBrowser.java + * Connects to an app's [`MediaBrowser`](https://developer.android.com/reference/android/media/browse/MediaBrowser) to determine whether SystemUI is able to connect and find a recent [`MediaItem`](https://developer.android.com/reference/android/media/browse/MediaBrowser.MediaItem) +* Factory classes (for unit testing): + * LocalMediaManagerFactory.kt + * MediaBrowserFactory.java + * MediaControllerFactory.java + * ResumeMediaBrowserFactory.java + +## Miscellaneous + +Other useful documents: + +* [go/sysui-media-resumption-requirements](https://goto.google.com/sysui-media-resumption-requirements) - Internal documentation for app developers about how to work with media resumption +* [Playing nicely with media controls](https://android-developers.googleblog.com/2020/08/playing-nicely-with-media-controls.html) - blog post on the Android 11 updates +* [Media Controls developer guide](https://developer.android.com/guide/topics/media/media-controls) |