Accessing Activity which started an Started Service after the activity is destroyed

Question

I think I can pass a reference of an Activity which started an Started Service . Since the service has a reference of the Activity, it may call methods of that reference.

Now if the Activity gets destroyed, but the service still running in background, what happens if the service calls a method of the reference of the activity?

Answer 1

You definitely should avoid storing references to activities in general. If so, you have to release it in activity's onDestroy() , otherwise you can get memory leak. What is your reason to store reference in a service?

EDIT:

You can use toast notifications or status Bar notifications to notify the user the background work has completed. It's a common practice. If you need to communicate with an Activity , there are several ways to accomplish it. You can bind to an Activity , use Intents or use AIDL . You can see more details here .

I describe one of the options using Intents along with ResultReceiver .

Service runs in the main thread of the application, so if you are performing blocking operations you should start a new thread inside the service. In this case you can use IntentService which simplifies the work for you and already implements threading stuff.

I will make a custom ServiceResultReceiver extended from ResultReceiver . Than I implement its interface in my Activity and when starting the Service I pass receiver object to IntentService .

Custom ResultReceiver :

public class ServiceResultReceiver extends ResultReceiver {

    private Receiver mReceiver;

    public ServiceResultReceiver(Handler handler) {
        super(handler);
    }

    public void setReceiver(Receiver receiver) {
        mReceiver = receiver;
    }

    public interface Receiver {
        public void onReceiveResult(int resultCode, Bundle resultData);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {
        if (mReceiver != null) {
            mReceiver.onReceiveResult(resultCode, resultData);
        }
    }
}

Your Activity :

public class MyActivity extends Activity implements ServiceResultReceiver.Receiver {
    private ServiceResultReceiver mReceiver;
    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        mReceiver = new ServiceResultReceiver(new Handler());
        mReceiver.setReceiver(this);
        // starting a service
        final Intent intent = new Intent(this, MyService.class);
        intent.putExtra("receiver", mReceiver);
        startService(intent);
    }
    ...

    @Override
    public void onReceiveResult(int resultCode, Bundle resultData) {
        // here you can handle data which came from your service.
        Toast.makeText(this, "onReceiveResult()", Toast.LENGTH_SHORT).show();
    }

Your Service :

public class MyService extends IntentService {
    ...
    @Override
    protected void onHandleIntent(Intent intent) {
        // executing your task
        ...
        // getting the receiver and sending back data in Bundle (here in this example we are sending no data)
        final ResultReceiver receiver = intent.getParcelableExtra("receiver");
        if (receiver != null) {
            receiver.send(0, null);
        }
    }
}