Android AsyncTasks How to Check If activity is still running

Question

I have used AsyncTasks with my application, in order to lazy download and update the UI.

For now my AsyncTasks updates the UI real simply:

protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
        gender.setText(values[0]);
}

My problem is how to check if the activity which the gender TextView rendered from, is still available?

If not, I will get an error and my application will shut down.

Answer 1

You can cancel your asynctask in the activity's onDestroy

@Override
protected void onDestroy() {
    asynctask.cancel(true);
    super.onDestroy();
}

and when performing changes you check whether your asynctask has been cancelled(activity destroyed) or not

protected void onProgressUpdate(String... values) {
    super.onProgressUpdate(values);
    if(!isCancelled()) {
         gender.setText(values[0]);
    }
}

Answer 2

I had a similar problem - essentially I was getting a NPE in an async task after the user had destroyed the fragment. After researching the problem on Stack Overflow, I adopted the following solution:

volatile boolean running;

public void onActivityCreated (Bundle savedInstanceState) {

    super.onActivityCreated(savedInstanceState);

    running=true;
    ...
    }


public void onDestroy() {
    super.onDestroy();

    running=false;
    ...
}

Then, I check "if running" periodically in my async code. I have stress tested this and I am now unable to "break" my activity. This works perfectly and has the advantage of being simpler than some of the solutions I have seen on SO.