IssueTracker

This is not a Navigation issue, but an issue with Fragments, so I'm moving it to that component.

It seems to me that you are popping the Fragment off the back stack that contains the shared element View that you're trying to use. When a Fragment is popped off the back stack, its Views are detached and destroyed, so I'm curious on your use case where you're expecting those Views to still exist?

My use case seems pretty common when you want to move forward in the stack with a shared element transition and doesn't want to go back to that screen but another screen previously added to the stack.
I understand the screen is detached since it's not added to the stack but then shouldn't that screen wait for transition to complete befofe being detached?

Yep, it should work.

For future reference, this is the exception message I get running your sample (thanks, it was very helpful):

2018-12-07 11:10:56.152 19973-19973/com.example.samystudio.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.samystudio.myapplication, PID: 19973
    java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.Collection.contains(java.lang.Object)' on a null object reference
        at androidx.collection.MapCollections.retainAllHelper(MapCollections.java:481)
        at androidx.collection.ArrayMap.retainAll(ArrayMap.java:164)
        at androidx.fragment.app.FragmentTransition.captureOutSharedElements(FragmentTransition.java:801)
        at androidx.fragment.app.FragmentTransition.configureSharedElementsReordered(FragmentTransition.java:573)
        at androidx.fragment.app.FragmentTransition.configureTransitionsReordered(FragmentTransition.java:233)
        at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:133)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2424)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2372)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
        at androidx.fragment.app.FragmentManagerImpl$1.run(FragmentManager.java:733)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

This is currently one of our highest crashes. Is there a short term solution we can try or can we expect an update soon?

We had to remove our shared element transitions because of this crash with Navigation and popUpTo. Is there a better workaround?

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 0cd3b081e65a5a15e2d1a9bf32399cb10c4d07ae
Author: jbwoods <jbwoods@google.com>
Date:   Tue Jul 09 14:01:35 2019

    Fix NPE when combining pop with add transaction
   
    When adding a transaction with a shared transition after popping a
    transaction without a shared transition, if reordering is allowed, a NPE
    is thrown. This ensures that the reordered transactions will not break.
   
    Test: Added Test
    BUG: 120507394
    Change-Id: Id37913b642cf4b4fe30ff52cfeed9f28be87f850

M       fragment/fragment/src/androidTest/java/androidx/fragment/app/FragmentTransitionTest.kt
M       fragment/fragment/src/main/java/androidx/fragment/app/FragmentTransition.java

https://android-review.googlesource.com/1013801
https://goto.google.com/android-sha1/0cd3b081e65a5a15e2d1a9bf32399cb10c4d07ae

This has been fixed internally and will be available in the Fragment 1.2.0-alpha02 release.