当屏幕关闭时，MediaPlayer.isPlaying会抛出IllegalStateException异常

Question

AudioService在构造函数中初始化MediaPlayer，并将其公开给Activity。

public class AudioService extends Service implements MediaPlayer.OnPreparedListener {

private static final String TAG = "AudioService";
MediaPlayer mMediaPlayer = new MediaPlayer();
private final IBinder mBinder = new AudioBinder();

public void onCreate () {
    mMediaPlayer.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);
    mMediaPlayer.setOnPreparedListener(this);
}

/** Called when MediaPlayer is ready */
public void onPrepared(MediaPlayer player) {
    player.start();
}

public AudioService() {}

public boolean initPlayer(final String section){
    try {
        AssetFileDescriptor afd = getAssets().openFd("records/"+section+".mp3");
        mMediaPlayer.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
        mMediaPlayer.prepareAsync();
        return true;
    }catch (IOException e){
        e.printStackTrace();
        return false;
    }
}

public MediaPlayer getPlayer(){
    return mMediaPlayer;
}

@Override
public IBinder onBind(Intent intent) {
    return mBinder;
}

@Override
public void onDestroy() {
    if (mMediaPlayer != null) mMediaPlayer.release();
}

public class AudioBinder extends Binder {
    AudioService getService() {
        return AudioService.this;
    }
}
}

我不知道是否可以直接从MediaPlayer操纵Activity。

public class PageActivity extends FragmentActivity {
    String TAG = "PageActivity";

    MediaPlayer player;
    Handler handler = new Handler();

    Button toggle;
    boolean isSeekBarDragging = false;

    String section;
    AudioService audioService;

    public ServiceConnection myConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName className, IBinder binder) {
            audioService = ((AudioService.AudioBinder)binder).getService();

        if(audioService.initPlayer(section)){
            player = audioService.getPlayer();
        }else {
            seekBar.setEnabled(false);
        }
        }

        @Override
        public void onServiceDisconnected(ComponentName className) {
            audioService = null;
            player = null;
        }
    };

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

        //bind service
        bindService(new Intent(this, AudioService.class), myConnection, Context.BIND_AUTO_CREATE);
    }

    private void initButtons() {
        toggle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //!!! Exception is thrown here.
                if(player.isPlaying()){
                    player.pause();
                }else {
                    player.start();
                }
            }
        });
    }

    @Override
    protected void onStop(){
        if(player.isPlaying()) player.stop();
        handler.removeCallbacks(updater);

        super.onStop();
    }
}