如何检查我的MediaBrowserSessionService是否正在运行

Question

我实现了一个音乐播放器但我的问题是，当我用关闭按钮关闭后打开应用程序音乐会自动停止。我想检查我的MediaBrowserSessionService是否正在运行或者告诉我其他方法。

private static final int STATE_PAUSED = 0;
private static final int STATE_PLAYING = 1;
private int mCurrentState;
private MediaBrowserCompat mMediaBrowserCompat;
private MediaControllerCompat mMediaControllerCompat;

private MediaBrowserCompat.ConnectionCallback mMediaBrowserCompatConnectionCallback = new MediaBrowserCompat.ConnectionCallback() {

    @Override
    public void onConnected() {
        super.onConnected();
        try {
            mMediaControllerCompat = new MediaControllerCompat(MainActivity.this, mMediaBrowserCompat.getSessionToken());
            mMediaControllerCompat.registerCallback(mMediaControllerCompatCallback);
            setSupportMediaController(mMediaControllerCompat);
            Log.i("Kunal","Kunal");
            MediaControllerCompat mediaControllerCompat=getSupportMediaController();
            Log.d("Controller", String.valueOf(mediaControllerCompat));
            Log.d("PlayBackState", String.valueOf(getSupportMediaController().getPlaybackState()));


        } catch( RemoteException e ) {

        }
    }
};




private MediaControllerCompat.Callback mMediaControllerCompatCallback = new MediaControllerCompat.Callback() {
    @Override
    public void onMetadataChanged(MediaMetadataCompat metadata) {
        super.onMetadataChanged(metadata);
    }

    @Override
    public void onPlaybackStateChanged(PlaybackStateCompat state) {
        super.onPlaybackStateChanged(state);
        if( state == null ) {
            return;
        }


        switch( state.getState() ) {
            case PlaybackStateCompat.STATE_PLAYING: {
                mCurrentState = STATE_PLAYING;
                MainActivity.this.startService(new Intent(MainActivity.this,BackgroundAudioService.class));
                break;
            }
            case PlaybackStateCompat.STATE_PAUSED: {
                mCurrentState = STATE_PAUSED;
                break;
            }
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getPermission();
    settingFirstSong();

        Log.i("Service","Running");
        mMediaBrowserCompat = new MediaBrowserCompat(this, new ComponentName(this, BackgroundAudioService.class),
                mMediaBrowserCompatConnectionCallback, this.getIntent().getExtras());
        mMediaBrowserCompat.connect();

    // Log.d("Controller", String.valueOf(mediaControllerCompat));

    /*if(getSupportMediaController().getPlaybackState().getState()==2)
    {
        getSupportMediaController().getTransportControls().playFromMediaId(CurrentlyPlayingSongData.getTrackPath(), null);
        getSupportMediaController().getTransportControls().seekTo(sharedPreferences.getInt("position",0));

    }*/

    songList = new SongList(this);
    songDataArrayList = songList.getData();

    BitmapExtraction bitmapExtraction = new BitmapExtraction(this, songDataArrayList);
    bitmapExtraction.bitmapExtraction();

    View bottomSheet = findViewById(R.id.design_bottom_sheet);
    BottomSheetBehavior behavior = BottomSheetBehavior.from(bottomSheet);
    behavior.setHideable(false);

    artistList = new ArtistList(this);
    artistDatas = artistList.getData();

    if (isNetworkAvailable()) {
        AddDataToArtistDB addDataToArtistDB = new AddDataToArtistDB(this, artistDatas);
        addDataToArtistDB.start();
    }

            Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
            setSupportActionBar(myToolbar);
            ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
            PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager());

            viewPager.setAdapter(pagerAdapter);
            TabLayout tabLayout = (TabLayout) findViewById(R.id.tab);
            tabLayout.setupWithViewPager(viewPager);


}

当我再次打开应用程序执行

时，这是我的实现

    getSupportMediaController().getTransportControls().playFromMediaId("any.mp3", null);

再一次，我的播放器是从我开始做的歌曲？

我的错误

  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.media.session.PlaybackStateCompat android.support.v4.media.session.MediaControllerCompat.getPlaybackState()' on a null object reference
                                                                            at com.techweblearn.musicplayer.MainActivity.onCreate(MainActivity.java:115)
                                                                            at android.app.Activity.performCreate(Activity.java:6303)
                                                                            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2402)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2509) 
                                                                            at android.app.ActivityThread.access$1000(ActivityThread.java:153) 
                                                                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373) 
                                                                            at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                            at android.os.Looper.loop(Looper.java:154) 
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5527) 
                                                                            at java.lang.reflect.Method.invoke(Native Method) 
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739) 
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:629)