Home » Android » java – Handle orientation change with running AsyncTask

java – Handle orientation change with running AsyncTask

Posted by: admin June 15, 2020 Leave a comment

Questions:

Use case:

The user start the app that will load a captcha. The user fill the captcha and try to download some information.

Problem:

If the user rotate the device while downloading the Activity is destroyed. At the end of the execution the AsyncTask is trying to update the destroyed Activity and the result is a “View not attached to window manager”.

“Wrong” solution:

I can mask the problem with a android:configChanges="orientation|keyboardHidden|screenSize" but with this the layout is not going to be updated to landscape.

What I’m asking:

Is it possible to change the orientation and change the “reference” of the Context passed to the AsyncTask?

This answer suggest to check if the dialog is not null, but it’s not what I’m looking for.

Here he suggests to use a WeakReference (here a nice snippet on how to use it) but I didn’t understand if it’s what I’m looking for.

To be more explicit this is what I’m doing in the onPostExecute:

@Override
protected void onPostExecute(Auto result) {
    progress.dismiss();
    new DownloaderCaptcha(context).execute("");
    ((EditText)context.findViewById(R.id.editTextCaptcha)).setText("");
    context.findViewById(R.id.progrBar).setVisibility(View.VISIBLE);
    context.findViewById(R.id.captcha).setVisibility(View.INVISIBLE);

    if(result != null) {
        Storage.storeHistory(context, result.getTarga().getValue());

        Intent i = new Intent(context, MenuActivity.class);
        i.putExtra("result", result);
        context.startActivity(i);
    } else {
        ErrorDialog.show(context, error);
    }
}
How to&Answers:

Here are my tips:

  • Do not use android:configChanges to address this issue.

  • Do not use Activity#onRetainNonConfigurationInstance() to address it either (as this approach is deprecated).

  • Instead, use a retained worker Fragment. I’ve recently posted an article describing how to handle configuration changes using retained Fragments. It solves the problem of retaining an AsyncTask across a rotation change nicely. You basically need to host your AsyncTask inside a Fragment, call setRetainInstance(true) on the Fragment, and report the AsyncTask‘s progress/results back to it’s Activity through the retained Fragment.

Answer:

“Wrong” solution:

I can mask the problem with a
android:configChanges=”orientation|keyboardHidden|screenSize” but with
this the layout is not going to be updated to landscape.

Actually it will.

android:configChanges Lists configuration changes that the activity
will handle itself. When a configuration change occurs at runtime, the
activity is shut down and restarted by default, but declaring a
configuration with this attribute will prevent the activity from being
restarted. Instead, the activity remains running and its
onConfigurationChanged() method is called.

Take a look at http://developer.android.com/guide/topics/manifest/activity-element.html#config

You can implement the layout for both Landscape and Portrait modes or to cancel your AsyncTask on configuration change.