android - 尝试使用 MediaPlayer 播放游戏背景音乐时出现空指针异常

Question

我试图复制：[http://stackoverflow.com/questions/11490236/android-comprehensive-failproof-music-service-across-multiple-activites][1] 但是，我得到一个空指针异常：StartupActivity .getService().musicStart(); 任何想法为什么这可能是空的？这是我的（删节的）主java版本：

public class homescreenfruit extends Activity {
// bounded service
private static MusicService mBoundService;

// whetere service is bounded or not
private boolean mIsBound;

SharedPreferences myPrefs;
SharedPreferences.Editor prefsEditor;
boolean snd1 = true;
boolean snd2 = true;
boolean snd3 = true;
Handler myHandler = new Handler();
// int lastsongplayed=1;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.homescreen);
    doBindService();
    myPrefs = this.getSharedPreferences("myPrefs", MODE_WORLD_READABLE);
    final SharedPreferences.Editor prefsEditor = myPrefs.edit();

        SoundManager.getInstance();
        SoundManager.initSounds(this);
        SoundManager.loadSounds();

        { // audio settings setup and run
            snd3 = myPrefs.getBoolean("snd3return", true);

        // ********************FIALS BELOW*********************
        if (snd3==true){
            homescreenfruit.getService().musicStart(); //  FAILS HERE WITH NPE
             }

    ImageButton ibs3 = (ImageButton) findViewById(R.id.sound3); // this is the music
    ibs3.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
             Log.e("sound3 start : ", " yep");
            ImageButton ibs3 = (ImageButton) findViewById(R.id.sound3);
            if (snd3==true){
                homescreenfruit.getService().musicStop();
                prefsEditor.putBoolean("snd3return", false); snd3=false;
                ibs3.setBackgroundResource(R.drawable.noteoff);
            }
            else if (snd3==false){
                prefsEditor.putBoolean("snd3return", true); snd3=true;
                ibs3.setBackgroundResource(R.drawable.noteon);
                homescreenfruit.getService().musicStart();
                // restart playing the music - add programming
                homescreenfruit.getService().musicStart();
            }
            prefsEditor.commit();  
        }
    });
final Runnable playmusic = new Runnable() // 
{
    public void run() {
         if (snd3==true){
             homescreenfruit.getService().musicStart();}
     }
};

public void onBackPressed() {
    if (snd3=true)
    SoundManager.playSound(96, 1);
    Log.e("onBack pressed", "onBack pressed");
    finish();
}

public void onPause() {
    super.onPause();
    if (snd3=true)
    {
        homescreenfruit.getService().musicPause();
    }
Log.e("onPause", "onPause");
}

public void onStop() {
    super.onStop();

    if (snd3=true){
    homescreenfruit.getService().musicStop();
    }
}

public void onResume() {
    super.onResume();
    if (snd3==true){

        homescreenfruit.getService().musicStart();
    }
}

public void onDestroy() {
    super.onDestroy();
    doUnbindService();
}


private final ServiceConnection mServiceConnection = new ServiceConnection() {

    // removed override
    public void onServiceConnected(ComponentName className, IBinder service) {
        setService(((MusicService.LocalBinder) service).getService());
    }

    // removed override
    public void onServiceDisconnected(ComponentName className) {
        setService(null);
    }
};

private void doBindService() {
    Intent service = new Intent(getBaseContext(), MusicService.class);
    // start service and bound it
    startService(service);
    bindService(new Intent(this, MusicService.class), mServiceConnection, Context.BIND_AUTO_CREATE);
    mIsBound = true;
}

private void doUnbindService() {
    if (mIsBound) {
        // Detach existing connection.
        unbindService(mServiceConnection);
        mIsBound = false;
    }
}

public static MusicService getService() {
    return mBoundService;
}

private static void setService(MusicService mBoundService) {
    homescreenfruit.mBoundService = mBoundService;
}

}

我已经按照链接实现了 CarefulMediaPlayer 和 Music Service。那是对的吗？