Android: Saving a state during Android lifecycle

Question

I am refering to http://developer.android.com/reference/android/app/Activity.html.

I have an activity which can be "interrupted" by the user, e.g. the user opens the menu to call the preferences screen. When calling the preference screen onSaveInstanceState(Bundle) is called and I can save my data. That's fine so far. But upon pressing the back button onRestoreInstanceState(Bundle savedInstanceState) is NOT called.

So how can I save my state? Do I have to do it when calling the new activity? But how?
The only way I can think of, is saving the state by passing the state to the new activity, do nothing there with the saved data, return it to the first activity and restore the state in onActivitResult. But that would mean that I have to pass data back and forth just to restore the state. Doesn't seem to be a nice solution.

Answer 1

Probably a bad answer, but are you sure onRestoreInstanceState needs to be called?

The point of the bundle and onSaveInstanceState / onCreate with bundle / onRestoreInstanceState is to save transient data for an activity that is in the history stack, in case the activity must be killed to reclaim some memory. If it is killed, the activity can be restored, as if it were never killed, via onCreate / onRestonreInstanceState. However, if the activity was not killed, there may be no need to restore its transient data - presumably it is just as it was.

The Android documentation is careful to point out that onSaveInstanceStae / onRestoreInstanceState are not lifecycle methods, so aren't guaranteed to be called during lifecycle state transitions. If you need to hook into certain lifecycle transitions, take a look at the lifecycle hook methods. For example, onResume is called when the activity becomes the foreground activity and onPause is called when it is no longer the foreground activity.