Question

I have this AsyncTask:

private class GetMyFlights extends AsyncTask<String, Void, Integer> {       
    private ProgressDialog dialog;  

    public GetMyFlights(ListActivity activity) {}           

    @Override
    protected Integer doInBackground(String... params) {
        return getData();
    }       

    @Override
    protected void onPostExecute(Integer result) {  
        super.onPostExecute(result);    
        //...
    }
}

When I change to another activity I want to stop it. So I set this:

@Override
protected void onPause() {
    if(mGetMyFlights != null){
        mGetMyFlights.cancel(true);
        Log.d(TAG, "MyFlights onPause, cancel task");
    }
    super.onPause();
}

But the code inside getData is still working when I change my activity. How can I be sure is stop?

Answer 1

What I usually do is call cancel(true) on the AsyncTask instance and check Thread.interrupted() in doInBackground. You could check isCancelled(), but that doesn’t work if the actual work is done in some other class that is independent from your AsyncTask and doesn’t know about it. For example (copied directly from my own getData() method, inside my Data class, independent from any activities, async tasks, etc.):

while ((line = reader.readLine()) != null) {
    if (Thread.interrupted()) throw new InterruptedException();
    content.append(line);
}

Just make sure to handle the InterruptedException in your doInBackground(), e.g.:

@Override
protected Integer doInBackground(String... params) {
    try {
        return getData();
    }
    catch (InterruptedException e) {
        Log.d("MyApp", "Girl, Interrupted");
        return -1;
    }
}

Also worth noting that onPostExecute() is not called if the task is cancelled. Instead, onCancelled() is called.