Question

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Ideal way to cancel an executing AsyncTask

When I developed an Android application, I used an AsyncTask to download something, I used a progressDialog to show the progress of this AsyncTask, now When I press the back button, I want to cancel this AsycTask, I invoked the AsycTask.cancel(), but it doesn’t work. How can I cancel a running AsyncTask ?

Answer 1

The most correct way to do it would be to check periodically inside doInBackground if the task was cancelled (i.e. by calling isCancelled). From http://developer.android.com/reference/android/os/AsyncTask.html:

Cancelling a task :

A task can be cancelled at any time by invoking
cancel(boolean). Invoking this method will cause subsequent calls to
isCancelled() to return true. After invoking this method,
onCancelled(Object), instead of onPostExecute(Object) will be invoked
after doInBackground(Object[]) returns. To ensure that a task is
cancelled as quickly as possible, you should always check the return
value of isCancelled() periodically from doInBackground(Object[]), if
possible (inside a loop for instance.)

Check also this blog post if you need more information: http://vikaskanani.wordpress.com/2011/08/03/android-proper-way-to-cancel-asynctask/