Question

I’m doing an app which use the new Google Maps V2, when the Map Camera moves, I need to reload the points to the new camera position, I do it with a asynctask.

The problem is when I move the camera position multiple times, app loads the points multiples times. So, I cancel the async task when the camera is moved and I don’t load new point until the task is cancelled. I have an empty while loop to do it, Is there a better solution to do it?

// LOAD NEW POIS ASYNC
private void updatePoisInMap( ){

     ....

     if (refresh_pois_async != null) {
        refresh_pois_async.cancel(true);
        while (!refresh_pois_async.isCancelled()) {
        }    
     }
     refresh_pois_async = new RefreshPoisAsync( ).execute( lowerLeftCorner, topRightCorner);
}

Answer 1

Actually, I don’t think your while loop will work, or at least not as you would expect it to. The AsyncTask.isCancelled() method is normally used inside the doInBackground() method, to support early cancellation. You have several options to do what you want:

• override the onCancelled() method of your AsyncTask. This is guaranteed to be called on the main thread when your doInBackground() is finished and you called cancel() on your task beforehand. In your onCancelled() you can then start a new AsyncTask. Use the isCancelled() in your Task’s doInBackground() for early exit, as described above.
• don’t cancel the current task, but let it run. In the meantime the user may move the map multiple times. As long as a task is still running, just set a flag that it should be rerun. At task completion (override onPostExecute() in your AsyncTask) check the flag and start over if it was set.
• combine the above to find the right balance between responsiveness (start loading the right POIs quick enough) and over-processing (don’t start every time, but wait for the user to stop scrolling).