IssueTracker

I don't know if this is something that can be changed, but I'll look into it.

Hmm... it is supposed to work like this, but you are seeing a bug.

It cou8ld be tricky to get this right because the onAnimationEnd() and onTransitionEnd() often modify the state. We must execute the Runnable only after the state has been changed to its final value.

I think it could be dangerous to make a change, but it is possible to run all the internal listeners first, then run all of the external ones with the Runnable executed between. Again, it wouldn't be safe because we can't guarantee that only the internal listeners change the system state.

Passing to Jeremy to get his thoughts

What we really need is a signal to say when all transitions are done and with it running early, we don't have that. For fragments this means that we could end up moving the fragment to RESUMED before all the transitions are actually completed and execute some code that is normally fine when the system is settled, but dangerous when it is not.

If moving onTransitionEnd() might be too dangerous are there other options? If you are in the animateToStart case should you even get an onTransitionEnd(). Maybe all external listeners get is an onTransitionCancel() since you are reversing a transition you started in the middle of it. Is that a safer signal to send back?

I think it is okay to separate the signals as long as they are explicit, but we for sure need a way to know that the Transition system is completely done doing any work and our Views are back in the original state that we passed them in.

Maybe you could notify at the end of your animateToStart lambda?

Per offline discussion, we can move ahead with the solution suggested in comment#4 and run external listeners last.

This will change the current order:

start transition > animateToStart > onTransitionEnd() > Runnable > finish up transition work

to

start transition > animateToStart > Runnable > finish up transition work > onTransitionEnd()


This has the implications that if developers are doing something with a specific result in their onTransitionEnd() callback, they will also need to handle the cancellation case by overriding the new onTransitionEnd(Transition, boolean).

For example, if there is a transition from View_A to View_B and the onTransitionEnd() callback has logic that expects View_B to be the final state, it will now need to add some additional logic based on the boolean in the case that View_A is the final state.

The following release(s) address this bug.It is possible this bug has only been partially addressed:

• androidx.transition:transition:1.5.0-alpha06

Thanks, we'll take another look.

This has been fixed internally and will be available in the Fragment 1.7.0-beta01 release.

Thank you for your work.
Are the changes mentioned in #comment12 the internal fix? I have used the AndroidX snapshot build with this fix included and stumbled uponan occasional crash when navigating back using the gesture before the animation has finished. Also leakcanary is still complaining and dumping the same stack trace as posted before and using the back button in the toolbar sometimes leads to an undefined state where the second fragment is still shown but we should see the first fragment. I put a screen recording of all cases in the attachment.

FATAL EXCEPTION: main
Process: com.example.pbfragmentsharedelement, PID: 3103
java.lang.IllegalStateException: setCurrentPlayTimeMillis() called after animation has been started
	at androidx.transition.Transition$SeekController.setCurrentPlayTimeMillis(Transition.java:2778)
	at androidx.transition.FragmentTransitionSupport.setCurrentPlayTime(FragmentTransitionSupport.java:265)
	at androidx.fragment.app.DefaultSpecialEffectsController$TransitionEffect.onProgress(DefaultSpecialEffectsController.kt:798)
	at androidx.fragment.app.SpecialEffectsController.processProgress(SpecialEffectsController.kt:441)
	at androidx.fragment.app.FragmentManager$1.handleOnBackProgressed(FragmentManager.java:513)
	at androidx.activity.OnBackPressedDispatcher.onBackProgressed(OnBackPressedDispatcher.kt:255)
	at androidx.activity.OnBackPressedDispatcher.access$onBackProgressed(OnBackPressedDispatcher.kt:63)
	at androidx.activity.OnBackPressedDispatcher$2.invoke(OnBackPressedDispatcher.kt:129)
	at androidx.activity.OnBackPressedDispatcher$2.invoke(OnBackPressedDispatcher.kt:127)
	at androidx.activity.OnBackPressedDispatcher$Api34Impl$createOnBackAnimationCallback$1.onBackProgressed(OnBackPressedDispatcher.kt:388)
	at android.window.WindowOnBackInvokedDispatcher$OnBackInvokedCallbackWrapper.lambda$onBackStarted$0(WindowOnBackInvokedDispatcher.java:329)
	at android.window.WindowOnBackInvokedDispatcher$OnBackInvokedCallbackWrapper$$ExternalSyntheticLambda5.onProgressUpdate(Unknown Source:2)
	at android.window.BackProgressAnimator.updateProgressValue(BackProgressAnimator.java:161)
	at android.window.BackProgressAnimator.-$$Nest$mupdateProgressValue(Unknown Source:0)
	at android.window.BackProgressAnimator$1.setValue(BackProgressAnimator.java:61)
	at android.window.BackProgressAnimator$1.setValue(BackProgressAnimator.java:57)
	at com.android.internal.dynamicanimation.animation.DynamicAnimation.setPropertyValue(DynamicAnimation.java:731)
	at com.android.internal.dynamicanimation.animation.DynamicAnimation.doAnimationFrame(DynamicAnimation.java:687)
	at android.animation.AnimationHandler.doAnimationFrame(AnimationHandler.java:344)
	at android.animation.AnimationHandler.-$$Nest$mdoAnimationFrame(Unknown Source:0)
	at android.animation.AnimationHandler$1.doFrame(AnimationHandler.java:87)
	at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1341)
	at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1352)
	at android.view.Choreographer.doCallbacks(Choreographer.java:952)
	at android.view.Choreographer.doFrame(Choreographer.java:878)
	at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1326)
	at android.os.Handler.handleCallback(Handler.java:958)
	at android.os.Handler.dispatchMessage(Handler.java:99)
	at android.os.Looper.loopOnce(Looper.java:205)
	at android.os.Looper.loop(Looper.java:294)
	at android.app.ActivityThread.main(ActivityThread.java:8248)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:552)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:971)

If you used a snapshot from this morning it should be fixed. Are you doing the same thing in these 3 cases and seeing different results? Could you further explain how you get these 3 cases?

I did use the very latest snapshot version from this morning.

There are 2 different ways to trigger an issue and both issues trigger the same leak from #comment8.

The first issue, leading to the crash in the stacktrace in #comment14, is to:
Press the button to open the second fragment and interrupt the opening animation by performing the back gesture (without seeking).
Press the second fragment button again before the closing animation is finished and interrupt the opening animation again using the back gesture.

The second issue, to get into an undefined state, is to:
Press the button to open the second fragment.
Press the back button in the toolbar at the time the opening animation is finishing.
The timing has to be just right but the issue can be triggered fairly consistently.

Both issues can be experienced using the project attached to #comment5

The behaviour described in the bug fix from #comment12 returned with https://android-review.googlesource.com/c/platform/frameworks/support/+/3017979

I am closing this as I have not been able to reliably produce any of the mentioned errors with the latest library versions and this bug was about providing support for shared elements, which did. I did see a case where if you use system back to interrupt, that the transition didn't finish, but I couldn't reproduce that either.

If you can provide an app that reproduces this case reliably please file a new bug.

The last issue with predictive back I've come across was fixed in fragment-1.8.5. Thanks for the fixes.