/**
   * Update the current media player state, optionally showing an error message.
   *
   * @param error if not null, error message to present to the user.
   */
  private void updatePlaybackState(String error) {
    LogHelper.d(TAG, "updatePlaybackState, playback state=" + mPlayback.getState());
    long position = PlaybackState.PLAYBACK_POSITION_UNKNOWN;
    if (mPlayback != null && mPlayback.isConnected()) {
      position = mPlayback.getCurrentStreamPosition();
    }

    PlaybackState.Builder stateBuilder =
        new PlaybackState.Builder().setActions(getAvailableActions());

    setCustomAction(stateBuilder);
    int state = mPlayback.getState();

    // If there is an error message, send it to the playback state:
    if (error != null) {
      // Error states are really only supposed to be used for errors that cause playback to
      // stop unexpectedly and persist until the user takes action to fix it.
      stateBuilder.setErrorMessage(error);
      state = PlaybackState.STATE_ERROR;
    }
    stateBuilder.setState(state, position, 1.0f, SystemClock.elapsedRealtime());

    // Set the activeQueueItemId if the current index is valid.
    if (QueueHelper.isIndexPlayable(mCurrentIndexOnQueue, mPlayingQueue)) {
      MediaSession.QueueItem item = mPlayingQueue.get(mCurrentIndexOnQueue);
      stateBuilder.setActiveQueueItemId(item.getQueueId());
    }

    mSession.setPlaybackState(stateBuilder.build());

    if (state == PlaybackState.STATE_PLAYING || state == PlaybackState.STATE_PAUSED) {
      mMediaNotificationManager.startNotification();
    }
  }
 public static int getMusicIndexOnQueue(Iterable<MediaSession.QueueItem> queue, long queueId) {
   int index = 0;
   for (MediaSession.QueueItem item : queue) {
     if (queueId == item.getQueueId()) {
       return index;
     }
     index++;
   }
   return -1;
 }