AsyncTask Cancel is not working

Question

I am learning how to cancel asyncTask so there is no uses on the code below.

I tried to called the asyncTask and execute it then cancel it and execute it.

Answer 1

You can use either

asynctask.cancel(true);

or

asyncTask.wait();

"true " if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete

Answer 2

My approach is slightly different and perhaps, a little lengthy. But it has always worked without any issues.

This piece of code goes in the doInBackground(). If you have a for... loop in it, then use the break; statement. If you do not use a for.... loop, remove it.

// CHECK IF THE USER HAS CANCELLED THE TASK
if (isCancelled())  {
    cancelTask = true; // (OPTIONAL) THIS IS AN ADDITIONAL CHECK I HAVE USED. THINK OF IT AS A FAIL SAFE.
    break; // REMOVE IF NOT USED IN A FOR LOOP
}

You already have an Asynctask declared: MyAsyncTask asyncTask = new MyAsyncTask();. Along with that, also create two instances of boolean. Call them, for example:

boolean blMyAsyncTask;
boolean cancelTask;

Now, in the onPreExecute(), toggle the status of the blMyAsyncTask instance:

blMyAsyncTask = true;

And in the onPostExecute():

blMyAsyncTask = false;

And, in the same onPostExecute(), I also do the remainder functions after checking the state of the cancelTask boolean. For example:

if (cancelTask == false)    {
    // THE NORMAL CODE YOU HAVE IN YOUR onPostExecute()
}

Finally, in the onDestroy() (I use this, but I suspect the onPause() could work too. Never done it in the onPause() in all honesty), check the status of the boolean blMyAsyncTask

if (blMyAsyncTask== true)   {
    asyncTask.cancel(true);
}

As I said at the start, it is lengthy, perhaps even complicated, but it has never failed. I also think of this as a little modular if you would. If I have more Asycntasks added to the Activity, I can add another check in the onDestroy().

Answer 3

you should not call asyncTask.onCancelled(); directly. You can call cancel(true) and inside your doInBackground() you check for isCancelled().

Answer 4

To cancel a AsyncTask call the below line.

asyncTask.cancel();

onCancelled() is a override method that is executed when ever cancel is called.