Stopping AsyncTask Intermittently

Question

See the Upgrade section below for my modified solution.

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purpose

• Periodically poll URLs (for example, every 30 seconds), but only when activity is in the foreground
• Stop polling if activity is not in the foreground.

Periodic execution

• A handler object that receives a Runnable using a method postDelayed
• runAsyncTask is launched in the Runnable object method
• In onPostExecuteAsyncTask, the postDelayedHandler object object is called again
• In onResumeactivity, the postHandler object method is called
• In onPauseactivity, the removeCallbacksHandler object is invoked to remove pending Runnable messages in the message queue

Problem with poll cancellation

• Runnable onPause, , AsyncTask, doInBackground, Runnable onPostExecute ( , removeCallbacks onPause)

• ​​ boolean member shouldPoll
• true onResume, false - onPause
• onPostExecute AsyncTask , shouldPoll postDelayed Handler

• shouldPoll OK?
• , - (, , shouldPoll) ; , - AsyncTask onPostExecute

MainActivity

boolean shouldPoll = false;

@Override
protected void onResume() {
    super.onResume();
    shouldPoll = true;
    handler.post(pollURLRunnable);
}

@Override
protected void onPause() {
    shouldPoll = false;
    handler.removeCallbacks(pollURLRunnable);
    super.onPause();
}

final Handler handler = new Handler();

final Runnable pollURLRunnable = new Runnable() {
    public void run() {
        PollingAsyncTask pollTimestampAsyncTask = new PollingAsyncTask();
        pollTimestampAsyncTask.execute();
    }
};

AsyncTask

@Override
protected void onPostExecute(Result result) {
    if (result != null) {
        //Do something here
    }
    if (shouldPoll) {
        handler.postDelayed(pollURLRunnable, 10000);
    }
}

Update

MainActivity

@Override
protected void onResume() {
    super.onResume();
    handler.post(startIntentServiceRunnable);
    LocalBroadcastManager.getInstance(this).registerReceiver(statusBroadcastReceiver, new IntentFilter(Constants.MY_INTENT_FILTER));
}

@Override
protected void onPause() {
    handler.removeCallbacks(startIntentServiceRunnable);
    LocalBroadcastManager.getInstance(this).unregisterReceiver(statusBroadcastReceiver);        
    super.onPause();
}

final Handler handler = new Handler();

final Runnable startIntentServiceRunnable = new Runnable() {
    public void run() {
        Intent intent = new Intent(MainActivity.this, PollingService.class);
        startService(intent);
    }
};


final BroadcastReceiver statusBroadcastReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        //...
        //Do something useful with the extras from intent here
        //...
        handler.postDelayed(startIntentServiceRunnable, 2000);
    }
};

PollingService

@Override
protected void onHandleIntent(Intent intent) {
    //...
    //Perform the polling and prepare results here
    //...
    broadcastResults();

}

private void broadcastResults() {
    Intent intent = new Intent(Constants.MY_INTENT_FILTER);
    //...
    //Fill the intent extras with the data here
    //...
    LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}

Answer 1

AsyncTask, . runnable, .

    HandlerThread handlerThread = new HandlerThread("Background thread");
    handlerThread.start();
    handler = new Handler(handlerThread.getLooper());