显示“正在播放”卡片

2023-08-16 05:41| 来源: 网络整理| 查看: 265

在启动器后面或在后台播放媒体时，TV 应用必须显示“正在播放”卡片。通过此卡片，用户可返回当前正在播放媒体的应用。

当存在活动的 MediaSession 时，Android 框架会在主屏幕上显示“正在播放”卡片。该卡片包含媒体元数据，如专辑封面、名称和应用图标。当用户选择该卡片时，系统会打开相应的应用。

本课程介绍如何利用 MediaSession 类实现“正在播放”卡片。

图 1. 在后台播放媒体时显示“正在播放”卡片。

启动媒体会话

当您的应用准备播放媒体时，创建一个 MediaSession。以下代码段举例说明了如何设置适当的回调和标记：

Kotlin session = MediaSession(this, "MusicService").apply { setCallback(MediaSessionCallback()) setFlags( MediaSession.FLAG_HANDLES_MEDIA_BUTTONS or MediaSession.FLAG_HANDLES_TRANSPORT_CONTROLS ) } Java session = new MediaSession(this, "MusicService"); session.setCallback(new MediaSessionCallback()); session.setFlags(MediaSession.FLAG_HANDLES_MEDIA_BUTTONS | MediaSession.FLAG_HANDLES_TRANSPORT_CONTROLS);

注意：系统将仅为设置有 FLAG_HANDLES_TRANSPORT_CONTROLS 标记的媒体会话显示“正在播放”卡片。

显示“正在播放”卡片

系统仅为活动会话显示“正在播放”卡片。播放开始时，您必须调用 setActive(true)。此外，您的应用还必须请求音频焦点，如管理音频焦点中所述。

Kotlin private fun handlePlayRequest() { tryToGetAudioFocus() if (!session.isActive) { session.isActive = true } ... } Java private void handlePlayRequest() { tryToGetAudioFocus(); if (!session.isActive()) { session.setActive(true); } ... }

通过调用 setActive(false) 停用媒体会话或者另一个应用启动媒体播放时，系统会从启动器屏幕中移除该卡片。如果播放完全停止且没有活动的媒体，您的应用应立即停用媒体会话。如果播放暂停，您的应用应在延迟一段时间（通常为 5 到 30 分钟）后停用媒体会话。

更新播放状态

更新 MediaSession 中的播放状态，以便该卡片可以显示当前媒体的状态。

Kotlin private fun updatePlaybackState() { val position: Long = mediaPlayer ?.takeIf { it.isPlaying } ?.currentPosition?.toLong() ?: PlaybackState.PLAYBACK_POSITION_UNKNOWN val stateBuilder = PlaybackState.Builder() .setActions(getAvailableActions()).apply { setState(mState, position, 1.0f) } session.setPlaybackState(stateBuilder.build()) } private fun getAvailableActions(): Long { var actions = (PlaybackState.ACTION_PLAY_PAUSE or PlaybackState.ACTION_PLAY_FROM_MEDIA_ID or PlaybackState.ACTION_PLAY_FROM_SEARCH) playingQueue?.takeIf { it.isNotEmpty() }?.apply { actions = if (mState == PlaybackState.STATE_PLAYING) { actions or PlaybackState.ACTION_PAUSE } else { actions or PlaybackState.ACTION_PLAY } if (currentIndexOnQueue > 0) { actions = actions or PlaybackState.ACTION_SKIP_TO_PREVIOUS } if (currentIndexOnQueue < size - 1) { actions = actions or PlaybackState.ACTION_SKIP_TO_NEXT } } return actions } Java private void updatePlaybackState() { long position = PlaybackState.PLAYBACK_POSITION_UNKNOWN; if (mediaPlayer != null && mediaPlayer.isPlaying()) { position = mediaPlayer.getCurrentPosition(); } PlaybackState.Builder stateBuilder = new PlaybackState.Builder() .setActions(getAvailableActions()); stateBuilder.setState(mState, position, 1.0f); session.setPlaybackState(stateBuilder.build()); } private long getAvailableActions() { long actions = PlaybackState.ACTION_PLAY_PAUSE | PlaybackState.ACTION_PLAY_FROM_MEDIA_ID | PlaybackState.ACTION_PLAY_FROM_SEARCH; if (playingQueue == null || playingQueue.isEmpty()) { return actions; } if (mState == PlaybackState.STATE_PLAYING) { actions |= PlaybackState.ACTION_PAUSE; } else { actions |= PlaybackState.ACTION_PLAY; } if (currentIndexOnQueue > 0) { actions |= PlaybackState.ACTION_SKIP_TO_PREVIOUS; } if (currentIndexOnQueue < playingQueue.size() - 1) { actions |= PlaybackState.ACTION_SKIP_TO_NEXT; } return actions; } 显示媒体元数据

使用 setMetadata() 方法设置 MediaMetadata。使用媒体会话对象的这一方法，您可以向“正在播放”卡片提供有关曲目的信息，如名称、字幕和各种图标。以下示例假定您的曲目数据存储在自定义数据类 MediaData 中。

Kotlin private fun updateMetadata(myData: MediaData) { val metadataBuilder = MediaMetadata.Builder().apply { // To provide most control over how an item is displayed set the // display fields in the metadata putString(MediaMetadata.METADATA_KEY_DISPLAY_TITLE, myData.displayTitle) putString(MediaMetadata.METADATA_KEY_DISPLAY_SUBTITLE, myData.displaySubtitle) putString(MediaMetadata.METADATA_KEY_DISPLAY_ICON_URI, myData.artUri) // And at minimum the title and artist for legacy support putString(MediaMetadata.METADATA_KEY_TITLE, myData.title) putString(MediaMetadata.METADATA_KEY_ARTIST, myData.artist) // A small bitmap for the artwork is also recommended putBitmap(MediaMetadata.METADATA_KEY_ART, myData.artBitmap) // Add any other fields you have for your data as well } session.setMetadata(metadataBuilder.build()) } Java private void updateMetadata(MediaData myData) { MediaMetadata.Builder metadataBuilder = new MediaMetadata.Builder(); // To provide most control over how an item is displayed set the // display fields in the metadata metadataBuilder.putString(MediaMetadata.METADATA_KEY_DISPLAY_TITLE, myData.displayTitle); metadataBuilder.putString(MediaMetadata.METADATA_KEY_DISPLAY_SUBTITLE, myData.displaySubtitle); metadataBuilder.putString(MediaMetadata.METADATA_KEY_DISPLAY_ICON_URI, myData.artUri); // And at minimum the title and artist for legacy support metadataBuilder.putString(MediaMetadata.METADATA_KEY_TITLE, myData.title); metadataBuilder.putString(MediaMetadata.METADATA_KEY_ARTIST, myData.artist); // A small bitmap for the artwork is also recommended metadataBuilder.putBitmap(MediaMetadata.METADATA_KEY_ART, myData.artBitmap); // Add any other fields you have for your data as well session.setMetadata(metadataBuilder.build()); } 响应用户操作

当用户选择“正在播放”卡片时，系统会打开拥有该会话的应用。如果您的应用向 setSessionActivity() 提供了 PendingIntent，系统会启动您指定的 Activity，如下所示。否则，系统将会打开默认系统 Intent。您指定的 Activity 必须提供允许用户暂停或停止播放的播放控件。

Kotlin val pi: PendingIntent = Intent(context, MyActivity::class.java).let { intent -> PendingIntent.getActivity( context, 99 /*request code*/, intent, PendingIntent.FLAG_UPDATE_CURRENT ) } session.setSessionActivity(pi) Java Intent intent = new Intent(context, MyActivity.class); PendingIntent pi = PendingIntent.getActivity(context, 99 /*request code*/, intent, PendingIntent.FLAG_UPDATE_CURRENT); session.setSessionActivity(pi);

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