public void onConnected() {
   MediaControllerCompat controller =
       ((FragmentActivity) getActivity()).getSupportMediaController();
   LogHelper.d(TAG, "onConnected, mediaController==null? ", controller == null);
   if (controller != null) {
     onMetadataChanged(controller.getMetadata());
     onPlaybackStateChanged(controller.getPlaybackState());
     controller.registerCallback(mCallback);
   }
 }
 /**
  * Adds a callback to receive updates from the Session. Updates will be posted on the caller's
  * thread.
  *
  * @param callback The callback object, must not be null.
  */
 public void registerCallback(Callback callback) {
   registerCallback(callback, null);
 }