Question

i have a problem with binding a service to an activity in Android. The problem occurs in the activity:

public class ServiceTestActivity extends Activity {

private static final String TAG = "ServiceTestAct";
boolean isBound = false;
TestService mService;    

public void onStopButtonClick(View v) {
    if (isBound) {
        mService.stopPlaying();
    }
}
public void onPlayButtonClick(View v) throws IllegalArgumentException, IllegalStateException, IOException, InterruptedException {
    if (isBound) {
        Log.d(TAG, "onButtonClick");
        mService.playPause();
    } else {
        Log.d(TAG, "unbound else");
        Intent intent = new Intent(this, TestService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }
}


private ServiceConnection mConnection = new ServiceConnection() {

    @Override
    public void onServiceDisconnected(ComponentName name) {
        isBound = false;

    }

    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        LocalBinder binder = (LocalBinder) service;
        mService = binder.getService();
        isBound = true;         
    }
    };
}

isBound tells if the service (called TestService) is already bound to the activity.
mService is the reference to the service.

Now if i call “onPlayButton(..)” the first time, with the service not beeing bound, bindService(..) is called and isBound switches from false to true. Then if i call “onPlayButton(..)” again, it calls “playPause()” on the service object. To here everything works fine.

But i want “playPause()” to be called right after the service has been bound, so i changed my code to this:

public void onPlayButtonClick(View v) throws IllegalArgumentException, IllegalStateException, IOException, InterruptedException {
    if (isBound) {
        Log.d(TAG, "onButtonClick");
        mService.playPause();
    } else {
        Log.d(TAG, "unbound else");
        Intent intent = new Intent(this, TestService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
        mService.playPause();
    }
}

From this point on I get a NullPointerException, because mService doesn’t have a reference to the bound service, it’s still null. I checked that by logging the value of mService at different positions in the code.

Any tips on what I am doing wrong here? I am pretty new to programming (especially binding) services in android, but I still don’t see where the major differences between my to versions are.

Answer 1

One solution is to call playPause() in onServiceConnected(). Another solution is to call startService() with a custom intent that will tell the service to play. I think you might want to think about a redesign. I would try to design the service so that you can start and bind to the service when the activity starts and stop the service when the activity stops. If you need a service that will stay active past the lifetime of the activity, extend the Application class and you can start the service in the onCreate() method.