Android – Best practice: AsyncTask during orientation change

androidexceptionmultithreading

AsyncTask is a great thing to run complex tasks in another thread.

But when there is an orientation change or another configuration change while the AsyncTask is still running, the current Activity is destroyed and restarted. And as the instance of AsyncTask is connected to that activity, it fails and causes a "force close" message window.

So, I am looking for some kind of "best-practice" to avoid these errors and prevent AsyncTask from failing.

What I've seen so far is:

Disable orientation changes.(For sure not the way you should handle this.)
Letting the task survive and updating it with the new activity instance via onRetainNonConfigurationInstance
Just canceling the task when the Activity is destroyed and restarting it when the Activity is created again.
Binding the task to the application class instead of the activity instance.
Some method used in the "shelves" project (via onRestoreInstanceState)

Some code examples:

Android AsyncTasks during a screen rotation, Part I and Part II

ShelvesActivity.java

Can you help me to find the best approach which solves the problem best and is easy to implement as well? The code itself is also important as I don't know how to solve this correctly.

Best Answer

Do NOT use android:configChanges to address this issue. This is very bad practice.

Do NOT use Activity#onRetainNonConfigurationInstance() either. This is less modular and not well-suited for Fragment-based applications.

You can read my 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.

Related Solutions

Android – How to handle an AsyncTask during Screen Rotation

You can check out how I handle AsyncTasks and orientation changes at code.google.com/p/shelves. There are various ways to do it, the one I chose in this app is to cancel any currently running task, save its state and start a new one with the saved state when the new Activity is created. It's easy to do, it works well and as a bonus it takes care of stopping your tasks when the user leaves the app.

You can also use onRetainNonConfigurationInstance() to pass your AsyncTask to the new Activity (be careful about not leaking the previous Activity this way though.)

Android – java.lang.IllegalArgumentException: View not attached to window manager

I too get this error sometimes when I dismiss dialog and finish activity from onPostExecute method. I guess sometimes activity gets finished before dialog successfully dismisses.

Simple, yet effective solution that works for me

@Override
protected void onPostExecute(MyResult result) {
    try {
        if ((this.mDialog != null) && this.mDialog.isShowing()) {
            this.mDialog.dismiss();
        }
    } catch (final IllegalArgumentException e) {
        // Handle or log or ignore
    } catch (final Exception e) {
        // Handle or log or ignore
    } finally {
        this.mDialog = null;
    }  
}

Best Answer

Related Solutions

Android – How to handle an AsyncTask during Screen Rotation

Android – java.lang.IllegalArgumentException: View not attached to window manager

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