错误。 ServiceToo.startPlay（）＆＃39;在null对象引用上

Question

我在“绑定服务”中放置了用于停止，播放和暂停的按钮。当我点击MainActivity中的播放btn时，应用程序崩溃，ServiceToo.startPlay（）＆＃39;在null对象引用上。

如何在没有崩溃的情况下控制我的播放器。

  **This is the media player in the onCreate.in the Bound Service**

    public void onCreate() {
    mManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    buildNote();
    Toast.makeText(this, "Service Created", Toast.LENGTH_SHORT).show();
    songlist = new String[]
            {"android.resource://" + getPackageName() + "/" + R.raw.blipotron,
                    "android.resource://" + getPackageName() + "/" + 
R.raw.funk_game,
                    "android.resource://" + getPackageName() + "/" + 
R.raw.poofy_reel};


    tracks[0] = "android.resource://" + getPackageName() + "/" + 
R.raw.blipotron;
    tracks[1] = "android.resource://" + getPackageName() + "/" + 
R.raw.funk_game;
    tracks[2] = "android.resource://" + getPackageName() + "/" + 
R.raw.poofy_reel;
    mediaPlayer = MediaPlayer.create(getApplicationContext(), 
Uri.parse(tracks[currentTrack]));
    mediaPlayer.setOnCompletionListener(this);
    //container = STARTED;
    //mediaPlayer.start();

    Toast.makeText(this, "Service Created", Toast.LENGTH_SHORT).show();
}

这是在“绑定服务”

中创建的按钮方法

 public void onCompletion(MediaPlayer mp) {
         //mp.release();
        if (currentTrack < tracks.length -currentTrack) {
            currentTrack++;
            mp = MediaPlayer.create(this, Uri.parse(tracks[currentTrack]));
            mp.setOnCompletionListener(this);
            mp.start();
        }
    }

        public void play() {
            if (container == STOPPED) {
                mediaPlayer.start();
            }
        }

        public void stop() {
            if (container == STARTED){
                mediaPlayer.stop();
            }
        }

        public void pause() {
            if (container == STARTED){
                mediaPlayer.pause();
            }

findViewById(R.id.play_btn).setOnClickListener(this);
    findViewById(R.id.stop_btn).setOnClickListener(this);
    findViewById(R.id.pause_btn).setOnClickListener(this);

这是MainActivity中的实际onClick按钮

private AudioService serviceRef;


// On Click button instances
@Override
public void onClick(View v) {
    if (v.getId() == R.id.play_btn) {
        startService(new Intent(this, AudioService.class));
        serviceRef.play();
    } else if (v.getId() == R.id.stop_btn) {
        stopService(new Intent(this, AudioService.class));
        serviceRef.stop();
    } else if (v.getId() == R.id.pause_btn) {
        stopService(new Intent(this, AudioService.class));
        serviceRef.pause();
    }