问题
I have an activity A which contains fragment F. A shows F by pushing it onto fragment manager's back stack. This fragment may show a dialog(more specifically, a DialogFragment) D, also by pushing it to the same fragment manager's back stack.
I need to be able to dismiss dialog D under certain circumstances that are determined by fragment F. Normally I would check if D is on the fragment manager's back stack and use getFragmentManager().popBackStack() to remove it. But this doesn't work if the activity gets destroyed and then recreated:
Say I set "Don't keep activities" flag in Android Settings. Now I background the app. Activity gets destroyed, and the fragments are too. Now I foreground the app again. At what point do the fragments F and D get added to fragment manager's back stack? This is a screenshot I took after I put a breakpoint on A's onPostResume() method, which I assume is the very last one to run in the activity lifecycle, before the user can use the app:
You may notice that mAdded field contains 2 elements - those are the restored fragments F and D. But they are not on the back stack yet, as mBackStack is null!
I would like to be able to remove D, but Android won't let me do it, since it's waiting to restore pre-existing state of fragments and it won't add them to the back stack until some time after onPostResume.
So in essence, I can't remove the fragment from the stack, since it's not on the stack yet. And I also can't prevent it from being added to the stack at some point, since, as you can see from the screenshot above, fragment manager stores it in a separate list mAdded and there's no methods that I can use to remove it from mAdded.
How can I prevent a saved fragment from being restored?
回答1:
Maybe Im wrong but AFAIK AOS doesn't store the fragment backstack at all if activity stops. It could only restore the last shown fragment without all the previous fragments on a stack.
However you could store the stack and fragments state yourself. Just remove your dialog in onPause storing some flag via onSaveInstanceState and then in onResume restore it or don't.
来源：https://stackoverflow.com/questions/29525097/how-to-remove-fragment-from-fragment-manager-when-activity-is-restored-after-bei