MediaBrowser和MediaBrowserService连接操作时，传入的回调不回调

我想要的结果：MediaBrowser.ConnectionCallback回调连接结果

客户端代码：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(TAG, "onCreate: ");
    initView();
    mMediaBrowser = new MediaBrowser(this, new ComponentName(this, MusicService.class),mConnectionCallback,null );

}

@Override
protected void onStart() {
    super.onStart();
    mMediaBrowser.connect();
}

@Override
protected void onStop() {
    super.onStop();
    mMediaBrowser.disconnect();
}

private void initView() {
    mList = new ArrayList<>();
}

private MediaBrowser.ConnectionCallback mConnectionCallback = new MediaBrowser.ConnectionCallback(){
    @Override
    public void onConnected() {

        Log.d(TAG, "onConnected: ");
        if (mMediaBrowser.isConnected()){
            String mediaId = mMediaBrowser.getRoot();
            mMediaBrowser.unsubscribe(mediaId);
            mMediaBrowser.subscribe(mediaId,mBrowserSubscriptionCallback);
        }
    }

    @Override
    public void onConnectionSuspended() {

        Log.d(TAG, "onConnectionSuspended: ");
    }

    @Override
    public void onConnectionFailed() {

        Log.d(TAG, "onConnectionFailed: ");
    }
};

服务端代码：

@Override
public void onCreate() {
    super.onCreate();
    Log.d(TAG, "onCreate: ");
    mPlaybackState = new PlaybackState.Builder()
            .setState(PlaybackState.STATE_NONE, 0, 1.0f)
            .build();

    mSession = new MediaSession(this, "MusicService");
    mSession.setCallback(SessionCallback);//设置回调
    mSession.setFlags(MediaSession.FLAG_HANDLES_TRANSPORT_CONTROLS);
    mSession.setPlaybackState(mPlaybackState);
    setSessionToken(mSession.getSessionToken());

    mMediaPlayer = new MediaPlayer();
    mMediaPlayer.setOnPreparedListener(this);
    mMediaPlayer.setOnCompletionListener(this);
}
private MediaSession.Callback SessionCallback = new MediaSession.Callback() {
    @Override
    public void onCommand(@NonNull String command, @Nullable Bundle args, @Nullable ResultReceiver cb) {
        super.onCommand(command, args, cb);
    }
};