Transitions fail to return to original state after animateToStart() and beginDelayedTransition() [300157785]

Fixed

Bug

Status Update

No update yet.

Description

jb...@google.com

created issue #1

Sep 13, 2023 12:31AM

Component used: Transition Version used: 1.5.0-alpha02 Devices/Android versions reproduced on: API 34

If you do a gesture back in Fragments using transitions and cancel the gesture multiple times, after the first cancel, starting the gesture will result in the transition on the exiting view failing to run.

I believe the cause of this is that the beginDelayedTransition() called by with a 0 duration called by Fragment never triggers this onAnimatedEnd() callback in Visibility. That results in the visibility failing to be added removed from the overlay and so the subsequent transitions on the view do not run.

Here are logs synced with the calls from Fragment and Visibility. I would expect there to be an onAnimationEnd reversed=false log before the onTransitionEnd in Visibility.

 V  Animating to start (in Fragment)
 D  onAnimationEnd reversed=true (in Visibility)
 V  Calling beginDelayedTransition (in Fragment)
 D  onTransitionEnd (in Visibility)
 V  On transitionEnd of beginDelayedTransition (in Fragment)

The can be reproduced by patching in aosp/2748867 and doing the following in the navigation-integration app:

Launch App
Press the "Navigate Next" button 2 times to get to the "two" screen
Start a gesture back to the "one" screen and cancel it
Start another gesture back to the "one" screen and the "two" screen will immediately go blank

Comments

mo...@google.com <mo...@google.com> Sep 13, 2023 04:31PM

Accepted by mo...@google.com.

mo...@google.com <mo...@google.com> #2Sep 18, 2023 08:29PM

Assigned to jb...@google.com.

Found the issue, ugh

Noticed that when I do the following:
transaction.addToBackStack(null)

When adding a Fragment with ViewPager2, the above issue occurs, although, idk if it's becaugh of gcFragments() anymore.

As soon as I un-comment that line, the issue disappears.

va...@google.com <va...@google.com> #3Sep 21, 2023 06:57PM

https://github.com/PenguinDan/ViewPagerCrash

Is the Sample application, to reproduce, move back really fast between page 2 -> 1 and vice versa (they are bottom buttons) a couple times.
Wait a couple seconds and page 1 (the black page) should turn white meaning the Fragment has been removed.

As soon as you comment line 40 on MainActivity, and attempt again, the error does not persist

va...@google.com <va...@google.com> #4Sep 21, 2023 07:08PM

Woops, sorry, If you guys had the previous ViewPagerCrash test app, I forgot to push (was exhasuted after debugging) I pushed one more time for the latest reproducible code

jb...@google.com <jb...@google.com> #5Sep 26, 2023 08:12PM

We'll have a look, thanks for reporting and repro steps / sample app. Stay tuned for updates on this issue.

jb...@google.com <jb...@google.com> #6Sep 26, 2023 08:46PM

Got to debug this now. Your sample indeed showcases an issue, so thanks for reporting and for the sample!

`transaction.addToBackStack(null)` adds the Fragment replacement transaction to the back stack, so you can go back to the previous state with the back button. Is that what you were looking to achieve? You said it works without it, which might help in the meantime.

Would you mind describing the use-case, so I better understand what you're trying to achieve? E.g. in the example, by switching between buttons 1 and 2 at some point you achieve multiple stack entries going back to the ViewPager2 Fragment.

ap...@google.com <ap...@google.com> #7Sep 26, 2023 08:56PM

Mostly for my notes, but the trace below explains what happens. Still need to work out why.

We have 5 instances of FragmentStateAdapter below.
Notice how in lines 36-39 4 different instances of FragmentStateAdapter perform a scheduled gc (after grace period expires).
Those don't have the Fragments bound to their ViewHolders as those were removed: lines 8, 16, 24, 32.

At the same time, com.test.myapplication.VPAdapter.createFragment(ViewPagerFragment.kt:161) only gets called once, so presumably all 5 have a reference to that same Fragment.

Needs more investigation as looks fishy.

1 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be modified at FragmentStateAdapter.<init>(FragmentStateAdapter.java:85). Current value = 'null'. New value = 'instance of androidx.collection.LongSparseArray(id=11289)'
2 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
3 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:174)
4 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
5 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:235)
6 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:240)
7 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
8 {FragmentStateAdapter@11,288}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onViewRecycled(FragmentStateAdapter.java:391)
9 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be modified at FragmentStateAdapter.<init>(FragmentStateAdapter.java:85). Current value = 'null'. New value = 'instance of androidx.collection.LongSparseArray(id=11307)'
10 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
11 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:174)
12 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
13 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:235)
14 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:240)
15 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
16 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onViewRecycled(FragmentStateAdapter.java:391)
17 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be modified at FragmentStateAdapter.<init>(FragmentStateAdapter.java:85). Current value = 'null'. New value = 'instance of androidx.collection.LongSparseArray(id=11314)'
18 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
19 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:174)
20 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
21 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:235)
22 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:240)
23 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
24 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onViewRecycled(FragmentStateAdapter.java:391)
25 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be modified at FragmentStateAdapter.<init>(FragmentStateAdapter.java:85). Current value = 'null'. New value = 'instance of androidx.collection.LongSparseArray(id=11316)'
26 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
27 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:174)
28 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
29 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:235)
30 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:240)
31 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
32 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onViewRecycled(FragmentStateAdapter.java:391)
33 {FragmentStateAdapter@11,317}.mItemIdToViewHolder will be modified at FragmentStateAdapter.<init>(FragmentStateAdapter.java:85). Current value = 'null'. New value = 'instance of androidx.collection.LongSparseArray(id=11318)'
34 {FragmentStateAdapter@11,317}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.itemForViewHolder(FragmentStateAdapter.java:234)
35 {FragmentStateAdapter@11,317}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:174)
36 {FragmentStateAdapter@11,306}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.gcFragments(FragmentStateAdapter.java:221)
37 {FragmentStateAdapter@11,313}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.gcFragments(FragmentStateAdapter.java:221)
38 {FragmentStateAdapter@11,315}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.gcFragments(FragmentStateAdapter.java:221)
39 {FragmentStateAdapter@11,317}.mItemIdToViewHolder will be accessed at FragmentStateAdapter.gcFragments(FragmentStateAdapter.java:221)

jb...@google.com <jb...@google.com> #8Oct 25, 2023 12:42AM

Reassigned to mo...@google.com.

Pausing the investigation for now until we better understand the use-case -- questions in

comment#6

AnimateToStartAlpha03.zip

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mo...@google.com <mo...@google.com> Nov 8, 2023 10:21PM

Accepted by mo...@google.com.

mo...@google.com <mo...@google.com> #9Nov 9, 2023 12:14AM

Yes, completely correct that I am attempting to use the back pressed implementation but also a bottom navigation implementation to switch to and from Fragments.

Currently the app that I am trying to make contains multiple Fragments with and without ViewPager2's accessible through a bottom navigation set of buttons. Through simple usage of moving to and from my ViewPager2 Fragments, I would see random instances of child Fragments disappearing from them.

mo...@google.com <mo...@google.com> #10Nov 9, 2023 06:18PM

I'd rather like to keep the "addToBackStack(..)" to rewind through fragment transactions. Will definitely look further into it also from the above mentioned logs.

ap...@google.com <ap...@google.com> #11Nov 10, 2023 11:27PM

Marked as fixed.

Thanks for clarifying, I will investigate further.

Following on the logs above, I suspect that each instance of FragmentStateAdapter gets access to that one BaseFragment in FragmentStateAdapter::restoreState (restore state called on each stack entry).
Making sure each ViewPagerFragment instance only gets access to its own state (so the state is not shared between them) should eliminate this issue.

Not sure where the problem lies yet, whether in ViewPager2's interaction with the state saving stack, or in the sample app, so continuing to investigate.

pr...@google.com <pr...@google.com> #12Nov 29, 2023 09:39PM

Yeah.. I have no clue what's going on, spending too much time debugging. I am planning to attach LifecycleObserver to my ViewHolder's so they act like Fragments.

From the evidence above, I am pretty sure it should not affect ViewHolder pattern but never know. Would love to know what was happening though if you come across a solution.