onPostExecute on cancelled AsyncTask

Question

Does onPostExecute execute if the AsyncTask has been cancelled?

If it does execute, is it safe to say that I should always ask if the task has been cancelled (isCancelled) at the start of onPostExecute, before doing anything else?

See also [this question](http://stackoverflow.com/q/10163763/165674). — Dheeraj Vepakomma, Apr 16 '12 at 05:10

score 68 · Accepted Answer · answered Apr 30 '13 at 14:05

The documented behaviour of onPostExecute on cancel() was changed between Android 2 and Android 4.

Android 2.3.7 onPostExecute :

Runs on the UI thread after doInBackground. The specified result is the value returned by doInBackground or null if the task was cancelled or an exception occured.

Android 4.0.1 onPostExecute :

Runs on the UI thread after doInBackground. The specified result is the value returned by doInBackground. This method won't be invoked if the task was cancelled.

So if you are still targeting Android 2 devices you should assume that onPostExecute will be called and in onPostExecute check for null result.

Extremely useful answer! – Ellen Spertus Mar 20 '14 at 03:15 — Ellen Spertus, Mar 20 '14 at 03:15
onCancelled will be called if you cancel the asynctask – Akshatha S R Oct 09 '19 at 08:21 — Akshatha S R, Oct 09 '19 at 08:21

score 8 · Answer 2 · answered Jul 26 '10 at 14:54

8

From my experience the onPostExecute() is actually not invoked when the task is cancelled. However, it may be possible to cancel the task after the task's doInBackground() is finished but before the onPostExecute() is invoked - in this case the onPostExecute() is actually invoked. Therefore, to be sure, I call the isCancelled() method in onPostExecute() and just "return" if the task has been cancelled. It works for me.

answered Jul 26 '10 at 14:54

Martin Vysny

3,088
28
39

1

Is it really true? I mean - how can I reproduce it? Any test code or idea on this? – Vit Khudenko Sep 07 '12 at 09:03
**_"Calling this method guarantees that onPostExecute(Object) is never subsequently invoked"_** https://developer.android.com/reference/android/os/AsyncTask.html#cancel%28boolean%29 – Joshua Pinter Feb 09 '21 at 23:05

score 7 · Answer 3 · edited May 23 '17 at 12:26

7

After checking the AsyncTask source code it seems that onPostExecute is invoked even if the task is cancelled. However, before calling onPostExecute the result is set to null (?) if the task has been cancelled.

Edit: @bain provides an updated answer.

edited May 23 '17 at 12:26

Community

1
1

answered Aug 06 '10 at 15:06

hpique

119,096
131
338
476

onPostExecute on cancelled AsyncTask

3 Answers3

Linked

Related