Android音乐控制接口RemoteController使用

转载出处：https://segmentfault.com/a/1190000000713535

Android RemoteController使用

原文链接
RemoteController在API 19 引进，用来给音乐控制提供标准接口。长久以来，音乐播放在Android平台没有一个标准的接口，所有播放器都使用自己的方式实现对音乐的控制，最常见的方式是在Service中进行音乐播放，通过PendingIntent进行播放事件的传递及控制，因此就带来了一个问题。任何一个第三方app无法通过标准方式获取到当前正在播放的音乐的信息，更无法进行控制。RemoteController的出现恰好解决了这个问题，RemoteController需要和RemoteControlClient配合使用，从命名上能够看出，RemoteController是控制及信息获取端的接口，用来进行音乐信息的获取以及音乐播放动作的发送。RemoteControlClient是播放器端的接口，用来获取并执行播放动作，同时讲当前播放状态信息进行同步。
然而相关文档介绍很少。

使用方式

1.继承 NotificationListenerService 并实现RemoteController.OnClientUpdateListener接口来创建remoteController对象并获取播放进度

  @TargetApi(Build.VERSION_CODES.KITKAT)public class MusicStateListener extends NotificationListenerService    implements RemoteController.OnClientUpdateListener {}

NotificationListenerService的主要作用是用来获取和操作通知栏通知，由于很奇葩的原因，为了获取合法的remoteController对象，必须实现这样一个NotificationListenerService并作为onClientUpdateListener传入remoteController来实现。

    public void registerRemoteController() {        remoteController = new RemoteController(this, this);        boolean registered;        try {          registered = ((AudioManager) getSystemService(AUDIO_SERVICE))              .registerRemoteController(remoteController);        } catch (NullPointerException e) {          registered = false;    }    if (registered) {      try {        remoteController.setArtworkConfiguration(            getResources().getDimensionPixelSize(R.dimen.remote_artwork_bitmap_width),            getResources().getDimensionPixelSize(R.dimen.remote_artwork_bitmap_height));        remoteController.setSynchronizationMode(RemoteController.POSITION_SYNCHRONIZATION_CHECK);      } catch (IllegalArgumentException e) {        e.printStackTrace();      }    }  }

RemoteController的初始化传入的两个参数分别是context和updateListener，而且此处的context必须是notificationListenerService

2.获取播放信息

合法register之后在回调中会接收到播放信息，包括播放/暂停等动作信息以及歌曲的meta信息

/** * Interface definition for the callbacks to be invoked whenever media events, metadata * and playback status are available. */public interface OnClientUpdateListener {    /**     * Called whenever all information, previously received through the other     * methods of the listener, is no longer valid and is about to be refreshed.     * This is typically called whenever a new {@link RemoteControlClient} has been selected     * by the system to have its media information published.     * @param clearing true if there is no selected RemoteControlClient and no information     *     is available.     */    public void onClientChange(boolean clearing);    /**     * Called whenever the playback state has changed.     * It is called when no information is known about the playback progress in the media and     * the playback speed.     * @param state one of the playback states authorized     *     in {@link RemoteControlClient#setPlaybackState(int)}.     */    public void onClientPlaybackStateUpdate(int state);    /**     * Called whenever the playback state has changed, and playback position     * and speed are known.     * @param state one of the playback states authorized     *     in {@link RemoteControlClient#setPlaybackState(int)}.     * @param stateChangeTimeMs the system time at which the state change was reported,     *     expressed in ms. Based on {@link android.os.SystemClock#elapsedRealtime()}.     * @param currentPosMs a positive value for the current media playback position expressed     *     in ms, a negative value if the position is temporarily unknown.     * @param speed  a value expressed as a ratio of 1x playback: 1.0f is normal playback,     *    2.0f is 2x, 0.5f is half-speed, -2.0f is rewind at 2x speed. 0.0f means nothing is     *    playing (e.g. when state is {@link RemoteControlClient#PLAYSTATE_ERROR}).     */    public void onClientPlaybackStateUpdate(int state, long stateChangeTimeMs,            long currentPosMs, float speed);    /**     * Called whenever the transport control flags have changed.     * @param transportControlFlags one of the flags authorized     *     in {@link RemoteControlClient#setTransportControlFlags(int)}.     */    public void onClientTransportControlUpdate(int transportControlFlags);    /**     * Called whenever new metadata is available.     * See the {@link MediaMetadataEditor#putLong(int, long)},     *  {@link MediaMetadataEditor#putString(int, String)},     *  {@link MediaMetadataEditor#putBitmap(int, Bitmap)}, and     *  {@link MediaMetadataEditor#putObject(int, Object)} methods for the various keys that     *  can be queried.     * @param metadataEditor the container of the new metadata.     */    public void onClientMetadataUpdate(MetadataEditor metadataEditor);};

音乐的meta信息从onClientMetadataUpdate回调中获取，能够获取到的字段包括歌手、名称、专辑名称、专辑封面等。注意此处获取到的专辑封面bitmap的尺寸是由注册remoteController时setArtworkConfiguration (int, int)来决定的

API文档

3.音乐控制

音乐的控制主要通过remoteController的sendMediaKeyEvent来实现
需要注意的是音乐的控制在逻辑上是模拟按钮的点击动作来实现的，所以在send一个keyCode时需要先后send KEY_ACTION_DOWN和KEY_ACTION_UP两个event来实现，所以我的实现是这样的

  public boolean sendMusicKeyEvent(int keyCode) {    if (!clientIdLost && remoteController != null) {      // send "down" and "up" key events.      KeyEvent keyEvent = new KeyEvent(KeyEvent.ACTION_DOWN, keyCode);      boolean down = remoteController.sendMediaKeyEvent(keyEvent);      keyEvent = new KeyEvent(KeyEvent.ACTION_UP, keyCode);      boolean up = remoteController.sendMediaKeyEvent(keyEvent);      return down && up;    } else {      long eventTime = SystemClock.uptimeMillis();      KeyEvent key = new KeyEvent(eventTime, eventTime, KeyEvent.ACTION_DOWN, keyCode, 0);      dispatchMediaKeyToAudioService(key);      dispatchMediaKeyToAudioService(KeyEvent.changeAction(key, KeyEvent.ACTION_UP));    }    return false;  }  private void dispatchMediaKeyToAudioService(KeyEvent event) {    AudioManager audioManager = (AudioManager) getSystemService(AUDIO_SERVICE);    if (audioManager != null) {      try {        audioManager.dispatchMediaKeyEvent(event);      } catch (Exception e) {        e.printStackTrace();      }    }  }

前面一部分是刚才讲到的通过remoteController来sendMediaKeyEvent，后面一部分是当remoteClient发生变化时remoteController的传递会失效，此时可以通过AudioManager来传递事件，

注意事项

1.注册RemoteController时OnClientUpdateListener必须是NotificationListenerService
2.发送KeyEvent时先发送ACTION_DOWN再发送ACTION_UP才是一个完整的事件；