Android Lifecycle management of Fragments within ViewPager and FragmentPagerAdapter

Question

I have been struggling to find out what the correct management of Fragments within a FragmentActivity with a ViewPager is. Before I go into details

Answer 1

It's lot to read, but after reading just introduction and the question and having experience with FragmentStatePagerAdapter, which is similar to FragmentPagerAdapter I can tell you that:

After rotation your adapter will AUTOMAGICALLY attach old fragments. So it seems that although activity creating adapter is being recreated, FragmentManager, which is global and it's instance preserve activity's recreation will detect that new FragmentStatePagerAdapter is combined with the same ViewPager and is asking for the same Fragments and will simply fetch them from Fragment's BackStack.

You as designer of Fragments can notice this behavior by continues invocation of Fragment.onAttach() and Fragment.onDetach(). When onAttach() occurs it's either creation of your Fragment or reusing it after rotation. You should be able to distinguish that Fragment was rotated with use of callback onRestoreRnstanceState().

You will see in your logs many onCreate() and other states logs simultaneously, because FragmentStatePagerAdapter always fetches/creates min 3 Fragments (except if you set that they are only 2 or 1), so also after screen rotation 3 fragments will be reattached from backstack.

I hope that it helped.