Crash in BrowseSupportFragment::ExpandPreLayout onPreDraw

Version used: androidx.leanback:leanback 1.0.0

Devices/Android versions reproduced on: low memory, different android versions

our investigation

Can you please change these line

if (getView() == null || getContext() == null) {

at the onPreDraw() method from the private ExpandPreLayout class in BrowseSupportFragment?

We need an additional check for isSavedState()/hasSavedState() to prevent the following user crash on low memory television devices:

Fatal Exception: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
       at androidx.fragment.app.FragmentManager.checkStateLoss(FragmentManager.java:64)
       at androidx.fragment.app.FragmentManager.ensureExecReady(FragmentManager.java:64)
       at androidx.fragment.app.FragmentManager.y(FragmentManager.java:1)
       at androidx.fragment.app.FragmentManager.P(FragmentManager.java:2)
       at androidx.fragment.app.FragmentManager.popBackStackImmediate(FragmentManager.java:504)
       at androidx.leanback.app.BrowseSupportFragment$3.run(BrowseSupportFragment.java:504)
       at androidx.leanback.app.BrowseSupportFragment$ExpandPreLayout.onPreDraw(BrowseSupportFragment.java:37)
       at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:977)
       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2484)

What happend?

The user is on a RowSupportFragment, so the Navigation is not expanded. The user clicked on a card to open the Detailscreen and play the selected Media. On low memory devices, so Activity with the BrowseSupportFragment is destroyed, the user navigates back and goto homescreen via homebutton. At this point, the ExpandPreLayout is called and try to run the given callback from the startHeadersTransitionInternal() via onExpandTransitionStart(). The Fragment is destroyed and so the App crashes with the given fatal exception.

Steps to reproduce:

We had a BrowseSupportFragment which contains the navigation. In this we add a Thread.sleep(1500) to onViewCreated() and onResume() to simulate low performing devices. We enable developer options and set "Don't Keep Activities" to true. No we can select a menu entry, navigate to a RowSupportFragment, open a Card and play the media. After this, we navigate back to the main screen and push the home button to leave the app with the playing media. The media is already playing and the app crashes few moments later.