Set a Listener in a Service-based Class

Question

Hy i have a problem to set the ServiceUpdateUIListener in the service to update the UI. It's wrong to make a new Service object and set there the listener and put it in an intent.

Code source is at http://developerlife.com/tutorials/?p=356 there i can't find how the set the listener and start the service right.

Calling:

TimerService service = new TimerService();
                TimerService.setUpdateListener(new ServiceUpdateUIListener() {

                    @Override
                    public void updateUI(String time) {
                        clock.setText(time);

                    }
                });

                Intent i  = new Intent(Timer.this,service.class); //service cannot be resolved to a type
                i.putExtra("ms", ms);
                startService(i);  

Service:

 public class TimerService extends Service{

        CountDownTimer timer;
        Chronometer clock;
        public static ServiceUpdateUIListener UI_UPDATE_LISTENER;

        @Override
        public IBinder onBind(Intent intent) {

            return null;
        }
        @Override
        public void onStart(Intent intent, int startId) {
            // TODO Auto-generated method stub
            int ms = intent.getIntExtra("ms", 0);

            timer = new  CountDownTimer(ms,1000){
                @Override
                public void onTick(long millisUntilFinished) {

                    int seconds = (int) (millisUntilFinished / 1000) % 60 ;
                    int minutes = (int) ((millisUntilFinished / (1000*60)) % 60);
                    int hours   = (int) ((millisUntilFinished / (1000*60*60)) % 24);

                    clock.setText( String.format("%02d:%02d:%02d", hours,minutes,seconds));
                    Log.e("Timer", String.valueOf(millisUntilFinished));

                }

                @Override
                public void onFinish() {
                    // TODO Auto-generated method stub

                }
            }.start();
            super.onStart(intent, startId);
        }
        public static void setUpdateListener(ServiceUpdateUIListener l) {
             UI_UPDATE_LISTENER = l;

        }

Answer 1

The Service documentation has fairly complete sample code for implementing a service in your app that another part of your app can bind to and make calls on:

http://developer.android.com/reference/android/app/Service.html#LocalServiceSample

Just put your setUpdateListener() method on the Service, and call it once you get onServiceConnected() with the service.

So your code would be something like this:

public interface UpdateListener {
    public void onUpdate(long value);
}

class LocalService {
    // Like in the Service sample code, plus:

    public static String ACTION_START = "com.mypackage.START";

    private final ArrayList<UpdateListener> mListeners
            = new ArrayList<UpdateListener>();
    private final Handler mHandler = new Handler();

    private long mTick = 0;

    private final Runnable mTickRunnable = new Runnable() {
        public void run() {
            mTick++;
            sendUpdate(mTick);
            mHandler.postDelayed(mTickRunnable, 1000);
        }
    }

    public void registerListener(UpdateListener listener) {
        mListeners.add(listener);
    }

    public void unregisterListener(UpdateListener listener) {
        mListeners.remove(listener);
    }

    private void sendUpdate(long value) {
        for (int i=mListeners.size()-1; i>=0; i--) {
            mListeners.get(i).onUpdate(value);
        }
    }

    public int onStartCommand(Intent intent, int flags, int startId) {
        if (ACTION_START.equals(intent.getAction()) {
            mTick = 0;
            mHandler.removeCallbacks(mTickRunnable);
            mHandler.post(mTickRunnable);
        }
        return START_STICKY;
    }

    public void onDestroy() {
        mHandler.removeCallbacks(mTickRunnable);
    }

Now you can start the service to get it to start counting, and anyone can bind to it to register a listener to receive callbacks as it counts.

It is really hard though to answer your question very well because you aren't really saying what you actually want to accomplish. There are a lot of ways to use services, either starting or binding or mixing the two together, depending on exactly what you want to accomplish.

Now you can implement your client code again based on the sample:

public class SomeActivity extends Activity implements UpdateListener {
    private LocalService mBoundService;

    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            mBoundService = ((LocalService.LocalBinder)service).getService();
            mBoundService.registerListener(this);
        }

        public void onServiceDisconnected(ComponentName className) {
            mBoundService = null;
        }
    };

    void doBindService() {
        bindService(new Intent(Binding.this, 
                LocalService.class), mConnection, Context.BIND_AUTO_CREATE);
        mIsBound = true;
    }

    void doUnbindService() {
        if (mIsBound) {
            if (mBoundService != null) {
                mBoundService.unregisterListener(this);
            }
            unbindService(mConnection);
            mIsBound = false;
        }
    }

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

Answer 2

I don't know exactly what you want, but this is not the way to do it. It seems you're mixing up a lot of things.

The tutorial itself is a bad example to my opinion, keeping a static reference to an activity in a service seems to me bad practice; you would use binding to bind your service to an activity, or if you don't want to you can pass Intents around.

As far as I know instantiating a service like you do and setting a listener on it like that doesn't work. You get an error in the startService() call because the service instance isn't a class obviously; you should use TimerService.class instead. In your service you have an onStart(); onStart() is a deprecated function, you should use onStartCommand() instead.

Now, if you have an activity in which you want to show a clock you don't need nor want the service to update its UI directly of course, but if you'd want the service to calculate a new clock tick for you, just call startService(); As long as your service is alive, sending a new start service intent will just call the onStartCommand() with the intent you're sending along.

If your clock is in an activity, setup a broadcast receiver inside your activity that and let your service broadcast an intent that can be received by the broadcast receiver you setup, with your new clock value passed along.