Android Activity and Service communication: how to keep the UI up-to-date

Question

I have an Activity A (not the main Activity) that launches a Service S that does some stuff in the background and, in the meanwhile, should made some changes to the UI of A.

Let's just say that S count from 0 to 100 and A should display this count in Real-Time. Since the real job of S is quite more complicated and CPU-consuming, I do not want to use AsyncTask for it (indeed "AsyncTasks should ideally be used for short operations (a few seconds at the most.) [...]") but just a regular Service started in a new Thread (an IntentService would be fine as well).

This is my Activity A:

public class A extends Activity {
    private static final String TAG = "Activity";
    private TextView countTextView;    // TextView that shows the number
    Button startButton;                // Button to start the count
    BResultReceiver resultReceiver;


    /**
     * Receive the result from the Service B.
     */
    class BResultReceiver extends ResultReceiver {
        public BResultReceiver(Handler handler) {
            super(handler);
        }

        @Override
        protected void onReceiveResult(int resultCode, Bundle resultData) {
            switch ( resultCode )  {
                case B.RESULT_CODE_COUNT:
                        String curCount = resultData.getString(B.RESULT_KEY_COUNT);
                        Log.d(TAG, "ResultReceived: " + curCount + "
");
                        runOnUiThread( new UpdateUI(curCount) );  // NOT WORKING AFTER onResume()!!!
                   break;
            }
        }
    }


    /**
     * Runnable class to update the UI.
     */
    class UpdateUI implements Runnable {
        String updateString;

        public UpdateUI(String updateString) {
            this.updateString = updateString;
        }

        public void run() {
            countTextView.setText(updateString);
        }
    }


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

        countTextView = (TextView) findViewById(R.id.countTextView);
        startButton = (Button) findViewById(R.id.startButton);

        resultReceiver = new BResultReceiver(null);
    }


    public void startCounting(View view) {
        startButton.setEnabled(false);

        //Start the B Service:
        Intent intent = new Intent(this, B.class);
        intent.putExtra("receiver", resultReceiver);
        startService(intent);
    }
}

And this is my Service B:

public class B extends Service {
    private static final String TAG = "Service";
    private Looper serviceLooper;
    private ServiceHandler serviceHandler;
    private ResultReceiver resultReceiver;
    private Integer count;

    static final int RESULT_CODE_COUNT = 100;
    static final String RESULT_KEY_COUNT = "Count";


    /**
     * Handler that receives messages from the thread.
     */
    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            while ( count < 100 ) {
                count++;
                //Sleep...
                sendMessageToActivity(RESULT_CODE_COUNT, RESULT_KEY_COUNT, count.toString());
            }

            //Stop the service (using the startId to avoid stopping the service in the middle of handling another job...):
            stopSelf(msg.arg1);
        }
    }


    @Override
    public void onCreate() {
        //Start up the thread running the service:
        HandlerThread thread = new HandlerThread("ServiceStartArguments", Process.THREAD_PRIORITY_BACKGROUND);
        thread.start();

        this.count = 0;

        //Get the HandlerThread's Looper and use it for our Handler
        serviceLooper = thread.getLooper();
        serviceHandler = new ServiceHandler(serviceLooper);
    }


    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        this.resultReceiver = intent.getParcelableExtra("receiver");

        //For each start request, send a message to start a job and deliver the start ID so we know which request we're stopping when we finish the job:
        Message msg = serviceHandler.obtainMessage();
        msg.arg1 = startId;
        serviceHandler.sendMessage(msg);

        //If we get killed, after returning from here, restart:
        return START_REDELIVER_INTENT;
    }


    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }


    /**
     * Send a message from to the activity.
     */
    protected void sendMessageToActivity(Integer code, String name, String text) {
        Bundle bundle = new Bundle();
        bundle.putString(name, text);

        //Send the message:
        resultReceiver.send(code, bundle);
    }
}

Everything works fine but if I click the back button (or the home button) and then I re-open the Activity A then the UI of A is not updated anymore (it just shows the initial configuration of A - i.e. the "startButton" is still clickable and the count is not showed - it seems runOnUiThread(...) is not working anymore). However, the Service B is still running in the background and the I can see the correct count is passed to the Activity A in the Log.d(...). Finally, if I click on the "startButton" again, the counting does not start from the beginning (0) but from where B has been arrived (I've double checked it by showing it in the notification bar).

How can I fix this behaviour? I would like that, when I re-open the Activity A, it automatically continues to receive and update the data from the Service B. Or, in other words, that the Service keeps the UI of the Activity A up-to-date.

Please give me some hints, links or piece of code. Thanks!

Android Activity and Service communication: how to keep the UI up-to-date

Answers (1)

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