Programmatically removing a ViewPager, when are (or how can I ensure) contained Fragments are destroyed?

Question

Having searched regarding this issue beforehand, I can find many discussions regarding dynamically adding and removing selected Fragments from a ViewPager. What I'm actually concerned about here however is how I can programmatically remove an entire ViewPager 'cleanly' from its containing ViewGroup, when that ViewPager has been used to display Fragments via a FragmentPagerAdapter, and ensure that the contained Fragments are destroyed properly.

To expand on the question a bit more, I have a landscape two-pane layout where a selection is made from a list within a Fragment on the left-hand-side, and chosen content is then placed on the right within a FrameLayout. The key thing is that the content may or may not be paginated. Therefore, the content must either be displayed in a ViewPager format, or if it is not paginated then it shall be represented by a single Fragment directly.

To show a single Fragment, I simply perform a FragmentTransaction as you normally would in order to place the Fragment into the FrameLayout container. If on the other hand it's paginated content to be shown, then instead I create a ViewPager and add it as a child of the FrameLayout.

When I need to change the content, then if the previous content was a stand-alone Fragment then I can simply remove it via FragmentTransaction .remove(). When I do this, the Fragment goes through the onPause() ... onDestroy() cycle as expected. If the previous content was a ViewPager then I remove it from the FrameLayout using .removeAllViews(). Here I come to the problem: I don't see any of the onPause() ... onDestroy() methods being called in any of the Fragments that were held within that ViewPager via the FragmentPagerAdapter.

From a user point of view, the application works fine. After several rounds of ViewPager being removed, I can see the GC reclaiming memory. However, I don't like the fact that those Fragments' end of life methods aren't called as I can't do any cleanup within them, and it just doesn't seem 'right'.

Is there a method I can hook into in order to remove the ViewPager's Fragments when the ViewPager is detached from its parent, perhaps? In other words, when I know that the ViewGroup is no longer in used, I would perform FragmentTransactions somewhere (perhaps in the FragmentPagerAdapter) to remove those Fragments.

Alternatively, I realise that I could just keep the ViewPager on the right permanently, and dynamically swap the Fragments within it. Of course it simply would not matter that at certain times it would only hold one page. If this would be a better way to go then I shall refactor my code to do this, but I would appreciate opinions.

Answer 1

However, I don't like the fact that those Fragments' end of life methods aren't called as I can't do any cleanup within them, and it just doesn't seem 'right'.

They should get cleaned up when the activity is destroyed, if that is not too late for you (e.g., heap issues).

In other words, when I know that the ViewGroup is no longer in used, I would perform FragmentTransactions somewhere (perhaps in the FragmentPagerAdapter) to remove those Fragments.

You did not execute the transactions to put the fragments there. Hence, you cannot readily execute the transactions to remove the fragments. If you switch to FragmentStatePagerAdapter, and call setAdapter(null), it should cause all existing fragments in the pager to be destroyed, by my reading of the source code. FragmentPagerAdapter never uses remove(), but FragmentStatePagerAdapter does, from its destroyItem() method, and all extant fragments are destroyed via destroyItem() when a new adapter (or null) is supplied to setAdapter().