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

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  1. POAndroid Activity and Service communication: how to keep the UI up-to-date
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    <p>I have an <strong>Activity A</strong> (not the main Activity) that launches a <strong>Service S</strong> that does some stuff in the background and, in the meanwhile, should made some changes to the UI of A. </p> <p>Let's just say that <strong>S count from 0 to 100</strong> and <strong>A should display this count in Real-Time</strong>. Since the real job of S is quite more complicated and CPU-consuming, I do not want to use <a href="http://developer.android.com/reference/android/os/AsyncTask.html" rel="nofollow">AsyncTask</a> for it (indeed <em>"AsyncTasks should ideally be used for short operations (a few seconds at the most.) [...]"</em>) but just a regular <a href="http://developer.android.com/guide/components/services.html" rel="nofollow">Service</a> started in a new Thread (an <a href="http://developer.android.com/reference/android/app/IntentService.html" rel="nofollow">IntentService</a> would be fine as well).</p> <p>This is my <strong>Activity A</strong>:</p> <pre><code>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 + "\n"); 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); } } </code></pre> <p>And this is my <strong>Service B</strong>:</p> <pre><code>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 &lt; 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); } } </code></pre> <p>Everything works fine but <strong>if I click the <em>back button</em> (or the <em>home button</em>) and then I re-open the Activity A then the UI of A is not updated anymore</strong> (it just shows the initial configuration of A - i.e. the "startButton" is still clickable and the count is not showed - it seems <em>runOnUiThread(...)</em> is not working anymore). However, <strong>the Service B is still running in the background</strong> and the I can see the correct count is passed to the Activity A in the <em>Log.d(...)</em>. 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).</p> <p>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.</p> <p>Please give me some hints, links or piece of code. Thanks!</p>
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