Background task, progress dialog, orientation change - is there any 100% working solution?
android, android-orientation, orientation
Solution
Step #1: Make your `AsyncTask` a `static` nested class, or an entirely separate class, just not an inner (non-static nested) class.
Step #2: Have the `AsyncTask` hold onto the `Activity` via a data member, set via the constructor and a setter.
Step #3: When creating the `AsyncTask`, supply the current `Activity` to the constructor.
Step #4: In `onRetainNonConfigurationInstance()`, return the `AsyncTask`, after detaching it from the original, now-going-away activity.
Step #5: In `onCreate()`, if `getLastNonConfigurationInstance()` is not `null`, cast it to your `AsyncTask` class and call your setter to associate your new activity with the task.
Step #6: Do not refer to the activity data member from `doInBackground()`.
If you follow the above recipe, it will all work. `onProgressUpdate()` and `onPostExecute()` are suspended between the start of `onRetainNonConfigurationInstance()` and the end of the subsequent `onCreate()`.
Here is a sample project demonstrating the technique.
Another approach is to ditch the `AsyncTask` and move your work into an `IntentService`. This is particularly useful if the work to be done may be long and should go on regardless of what the user does in terms of activities (e.g., downloading a large file). You can use an ordered broadcast `Intent` to either have the activity respond to the work being done (if it is still in the foreground) or raise a `Notification` to let the user know if the work has been done. Here is a blog post with more on this pattern.
Problem
I download some data from internet in background thread (I use `AsyncTask`) and display a progress dialog while downloading. Orientation changes, Activity is restarted and then my AsyncTask is completed - I want to dismiss the progess dialog and start a new Activity. But calling dismissDialog sometimes throws an exception (probably because the Activity was destroyed and new Activity hasn't been started yet). What is the best way to handle this kind of problem (updating UI from background thread that works even if user changes orientation)? Did someone from Google provide some "official solution"?