Is the Android service still alive even after the onDestroy() be called?

Question

For studying the Android service, I wrote a test program that have three button "bind service", "unbind service" and "send echo" on the screen. When clicked, they use bindService(), unbindService() and a Messenger to communicate with the service.

Here is the service codes:

public class MessengerService extends Service {

private final Messenger mMessenger = new Messenger(new TempHandler());
private class TempHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case MSG_SAY_HELLO:
            Toast.makeText(getApplicationContext(), "Hi, there.", Toast.LENGTH_SHORT).show();
            break;

        case MSG_SAY_GOODBYE:
            Toast.makeText(getApplicationContext(), "See you next time.", Toast.LENGTH_SHORT).show();
            break;

        case MSG_ECHO:
            Toast.makeText(getApplicationContext(), "Received " + msg.arg1 + " from client.", Toast.LENGTH_SHORT).show();

            Messenger replyMessenger = msg.replyTo;
            Message replyMsg = Message.obtain(null, MSG_ECHO, msg.arg1, 0);
            try {
                replyMessenger.send(replyMsg);
            } catch (RemoteException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        default:
            super.handleMessage(msg);
        }
    }

}

@Override
public IBinder onBind(Intent intent) {
    Toast.makeText(getApplicationContext(), "Service bound", Toast.LENGTH_SHORT).show();
    return mMessenger.getBinder();
}

@Override
public void onDestroy() {
    Log.d("", "Service.onDestroy()...");
    super.onDestroy();
}
}

And here is the activity code:

public class MessengerActivity extends Activity {
private Messenger mMessengerService;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity2);

    Button bind = (Button) findViewById(R.id.button5);
    bind.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            doBindService();
        }           
    });

    Button unbind = (Button) findViewById(R.id.button6);
    unbind.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            doUnbindService();
        }
    });

    Button echo = (Button) findViewById(R.id.button7);
    echo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            doSendEcho();
        }
    });
}

private void doBindService() {
    Intent intent = new Intent(getApplicationContext(), MessengerService.class);
    bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}

private void doUnbindService() {
    Message msg = Message.obtain(null, MessengerService.MSG_SAY_GOODBYE);
    try {
        mMessengerService.send(msg);
    } catch (RemoteException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    unbindService(mConnection);     
}

private void doSendEcho() {
    if (mMessengerService != null) {
        Message msg = Message.obtain(null, MessengerService.MSG_ECHO, 12345, 0);
        msg.replyTo = mMessenger;
        try {
            mMessengerService.send(msg);
        } catch (RemoteException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

private final Messenger mMessenger = new Messenger(new TempHandler());
private ServiceConnection mConnection = new ServiceConnection() {

    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        Toast.makeText(getApplicationContext(), "Service is connected.", Toast.LENGTH_SHORT).show();

        mMessengerService = new Messenger(service);

        Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO);
        try {
            mMessengerService.send(msg);
        } catch (RemoteException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {
        mMessengerService = null;
        Toast.makeText(getApplicationContext(), "Service is disconnected.", Toast.LENGTH_SHORT).show();
    }

};

private class TempHandler extends Handler {

    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case MessengerService.MSG_ECHO:
            Toast.makeText(getApplicationContext(), "Get the echo message (" + msg.arg1 + ")", Toast.LENGTH_SHORT).show();
            break;

        default:
            super.handleMessage(msg);
        }
    }

}
}

When I click "bind service" and "send echo" button. I can see the service is connected and the message communication is good. And then click "unbind service", I saw the service onDestroy() be called, so I expect the service is stopped and should not respond to the coming message again. But actually is, the service seems still alive and I could get the echo message again when click the "send echo" button. So I'm wondering is there anything I made incorrect? Or maybe I'm not fully understand about the service?

Hope someone can help, thanks.

Answer 1

I personally find the terminology/nomenclature to be dissatisfying/misleading. "onDestroy" and "stopService" might be better understood if they were called "FlagForAndroidOSDestruction" and "FlagForAndroidStopService".

If one downloads/compiles/runs any of the following examples, one can see that even when the OnHandleIntent is finished or stopService has been called, the process and even the service can still hang around! To see this simply launch the example(s) below, and then on your phone/tablet goto Settings->Apps->Running->Show Running Services and Settings->Apps->Running->Show Cached Processes

When you see these, try launching a ton of other apps on the phone and THEN you'll see Android destroying said service & process.

http://developer.android.com/guide/components/services.html#ExtendingIntentService

http://android-er.blogspot.com/2013/03/stop-intentservice.html

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