Predictive back transition ends prematurely in Navigation Compose [325998468]

Fixed

Bug

Status Update

No update yet.

Description

ky...@gmail.com

created issue #1

Feb 20, 2024 10:23AM

Component used: Navigation

Version used: 2.8.0-SNAPSHOT

Android versions reproduced on: U

Introduced in https://android-review.googlesource.com/c/platform/frameworks/support/+/2853474

PredictiveBackHandler(currentBackStack.size > 1) { backEvent ->
    inPredictiveBack = true
    progress = 0f
    val currentBackStackEntry = currentBackStack.lastOrNull()
    composeNavigator.prepareForTransition(currentBackStackEntry!!)
    val previousEntry = currentBackStack[currentBackStack.size - 2]
    composeNavigator.prepareForTransition(previousEntry)
    try {
        backEvent.collect {
            progress = it.progress
            logcat("NavHost") { "progress: $progress" }
        }
        inPredictiveBack = false
        composeNavigator.popBackStack(currentBackStackEntry, false)
    } catch (e: CancellationException) {
        inPredictiveBack = false
    }
}

When a regular back is performed, inPredictiveBack will be set to false immediately, causing the AnimatedContent to recompose.

Transition may not complete by the time but will jump to the final state.

Comments

il...@google.com <il...@google.com> #2Feb 22, 2024 12:08AM

Nested scrolling works partially (as per

http://b/122818889). Let's discuss if we need full support and if so make sure it works.

ky...@gmail.com <ky...@gmail.com> #3Feb 22, 2024 01:48AM

Hi!

What is 'partially' exactly?
How do I see it?
Thanks!

ky...@gmail.com <ky...@gmail.com> #4Feb 22, 2024 02:39AM

As of now:
- Nesting scroll views with a scroll direction perpendicular to the ViewPager2's orientation inside ViewPager2 works
- Nesting scroll views with a scroll direction parallel to the ViewPager2's orientation inside ViewPager2 does not work

navigation.mp4

1.4 MB

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jb...@google.com <jb...@google.com> Feb 23, 2024 01:00AM

Assigned to jb...@google.com.

ap...@google.com <ap...@google.com> #5Feb 27, 2024 02:23AM

Horizontal ViewPager2 not correctly working into a vertical RecyclerView
Set a setNestedScrollingEnabled to the RecyclerView into the ViewPager2 (across reflection) resolves the problem

jb...@google.com <jb...@google.com> #6Feb 28, 2024 04:03AM

Marked as fixed.

ageevvalentin@gmail.com, could you provide a sample app? I'd like to learn more about the circumstances that cause the problem; putting a clean ViewPager2 inside a clean RecyclerView seems to work fine, so there must be other factors involved.

ky...@gmail.com <ky...@gmail.com> #7Feb 28, 2024 04:05AM

Added a patch for androidx-master-dev that demos a horizontal ViewPager2 inside a vertical RecyclerView.

Verified that it works correctly on a:
- Nexus 4 emulator with API 17
- Nexus 5X emulator with API 28
- Pixel 2 device with API 29

To reproduce:
- Check out the Android Jetpack source (at commit 256899f482ff85cddfb050f37550be7b5ec927ef) (see steps in [1])
- Apply the patch (`git apply 0001-Add-sample-where-a-horizontal-ViewPager2-is-nested-i.patch`)
- Build and install viewpager2's integration-tests app: `./gradlew viewpager2:integration-tests:testapp:installDebug`
- Run it

Closing the issue for now, but please reopen if you have a minimal reproduction app

[1]

https://android.googlesource.com/platform/frameworks/support/+/256899f482ff85cddfb050f37550be7b5ec927ef

jb...@google.com <jb...@google.com> #8Feb 28, 2024 04:12AM

Re-opening as requested by a few users. Narrowed down the focus to nested scrolling elements with the same scroll direction.

na...@google.com <na...@google.com> #9Mar 6, 2024 07:49PM

Any progress on this? (only talking about the "same scroll direction" issue)

I searched a lot for workarounds on Google and SO, but it seems no one really found a suitable solution yet.
The thing is that all other VerticalViewPagers out there have other problems that are similarly annoying. Most of them revolve around touch issues like "What's a click and what's a swipe" or "what's the fling threshold to snap to the next page".

So if someone knows of a working sample of VerticalViewPagers, I'd be happy to see a link :)