Why the AsyncTask doesn't stop?

Question

Hi and thanks for your attention,

I have the following code, which

starts an AsyncTask when a button is pressed

and

should stop the AsyncTask when the button is released.

But this does not happen...

(the AsyncTask continues until its natural end, when the MAXX value is reached)

Please what am I doing wrong?

class right extends AsyncTask<Void, Void, Void> {
        @Override
        protected Void doInBackground(Void... unused) {
            while (x < MAXX) {
                if (x < MAXX)
                    x++;
                publishProgress();
                SystemClock.sleep(40);
            }
            return (null);
        }

        @Override
        protected void onProgressUpdate(Void... unused) {
            horizontal.scrollTo(x, 0);
            Log.e("x", Integer.toString(x));
        }

        @Override
        protected void onPostExecute(Void unused) {

        }
    }



    left.setOnTouchListener(new OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            right righttask = new right();
            switch (event.getAction()) {

            case MotionEvent.ACTION_DOWN:
                righttask.execute();
                break;
            case MotionEvent.ACTION_UP:
                righttask.cancel(true);
                Log.e("","SHOULD STOP ASYNCTASK!!!");
                break;
            }
            return false;
        }
    });

if you read the documentation for `cancel`, you'll see that it does not do what you want it to. (i don't see the point of the if condition, by the way.) — njzk2, Nov 27 '13 at 14:34

score 3 · Answer 1 · answered Nov 27 '13 at 14:35

3

Add this to your while loop :

if (isCancelled()) break;

More informations : Usage of AsyncTask

answered Nov 27 '13 at 14:35

A.S. · Answer 2 · 2013-11-27T15:09:27.307

2

Have a look at the Documentation

It is also defined that the doInBackGround() will not be canceled. Therefore you should check in your loop if the thread is canceled and break/leave it as mentioned in the example in the Documentation.

So you code should look loke this

        @Override
        protected Void doInBackground(Void... unused) {
            while (x < MAXX) {
                if (x < MAXX)
                    x++;
                publishProgress();
                if (isCancelled()) break;  //Add this line!
                SystemClock.sleep(40);
            }
            return (null);
        }

Sorry but I have to say a few more things:

Classes should have names with upper Case starting.
Why aren't you using a for loop when u want to increment x
Variables should start with lower case

so usually your code should look like this:

class Right extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... unused) {
        for(int x = 0; x < MAXX; x++){

            publishProgress();
            if (isCancelled()) break;  //Add this line!            
            SystemClock.sleep(40);
        }
        return (null);
    }

    @Override
    protected void onProgressUpdate(Void... unused) {
        horizontal.scrollTo(x, 0);
        Log.e("x", Integer.toString(x));
    }

    @Override
    protected void onPostExecute(Void unused) {

    }
}


Right righttask;  //make it global!
left.setOnTouchListener(new OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {

        switch (event.getAction()) {

        case MotionEvent.ACTION_DOWN:
            righttask = new Right();
            righttask.execute();
            break;
        case MotionEvent.ACTION_UP:
            righttask.cancel(true);
            Log.e("","SHOULD STOP ASYNCTASK!!!");
            break;
        }
        return false;
    }
});

edited Nov 27 '13 at 15:09

answered Nov 27 '13 at 14:37

A.S.

4,574
3
26
43

So try to take a thrad/runnable – A.S. Nov 27 '13 at 14:55
OH SHIT GIT IT! You are xreating a new Asymnctask every touchevent – A.S. Nov 27 '13 at 14:59
that is something I considered, let me check – Lisa Anne Nov 27 '13 at 15:00
So please define a global variable for the Right AsyncTask and initialize it in the onCreate or do it like my updated answer – A.S. Nov 27 '13 at 15:00
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/42048/discussion-between-a-s-and-lisa-anne) – A.S. Nov 27 '13 at 15:02
I have checked A.S, I do not start a new AsyncTaskaverytime :-((( – Lisa Anne Nov 27 '13 at 15:07
would be very happy to do so, but i am behind a firewall... :-((( – Lisa Anne Nov 27 '13 at 15:08
thanks A.S tried this way as well, but the doInBackground doesn't stop... :-(((( – Lisa Anne Nov 27 '13 at 15:21
made a new answer, hope it helps you see below pls – A.S. Nov 27 '13 at 15:26

score 1 · Answer 3 · edited May 23 '17 at 12:33

1

I think this post could be useful, maybe your problem is the same : Android AsyncTask won't stop when cancelled, why?

edited May 23 '17 at 12:33

Community

1
1

answered Nov 27 '13 at 14:39

Pull

2,236
2
16
32

A.S. · Accepted Answer · 2013-11-27T19:08:46.457

Hi there just left my working desk, and I do not have the IDE on my laptop so just writing a code out of mind, try to use a Runnable instead of a AsyncTask:

    //GLOABLS
boolean threadBool = false;
Handler handler;
    Thread thread;

onCreate(){
    handler = new Handler();


    left.setOnTouchListener(new OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {

            switch (event.getAction()) {

            case MotionEvent.ACTION_DOWN:

                threadBool = true;
                // handler.post(myRunabble);
                                    thread = newThread(myRunnable);
                                    thread.start();
                break;
            case MotionEvent.ACTION_UP:
                threadBool = false;
                break;
            }
            return false;
        }
    });
}

Runnable myRunnable = new Runnable() {
      @Override
      public void run() {
           for(int x = 0; x < MAXX; x++ ){
              handler.post(new Runnable(){
                  public void run() {
                     horizontal.scrollTo(x, 0);
              });
               if (threadBool == false){
                           threadBool = true;
                           break;
                       } 

               try{ Thrad.sleep(100); }catch(Exception e){} //catch the right one here
           }
      }
 };

if you only want to scroll in a listview you should also check `smoothScrollTo` — A.S., Nov 27 '13 at 15:27
Have a look at this: http://stackoverflow.com/questions/12716850/android-update-textview-in-thread-and-runnable — A.S., Nov 27 '13 at 15:55

Why the AsyncTask doesn't stop?

4 Answers4