Flows complete early in navigation-compose 2.4.0-alpha07 on tab reselection [196997433]

Fixed

Bug

Status Update

No update yet.

Description

yu...@gmail.com

created issue #1

Aug 18, 2021 03:11AM

Component used: Navigation Version used: Snapshot #7634339 or 2.4.0-alpha07 Devices/Android versions reproduced on: Pixel 4a

This issue is related to another fixed issue: https://issuetracker.google.com/issues/194925622

2.4.0-alpha05 introduced a bug where tab reselection causes empty screens, unless the current screen is the startDestination of the root graph.

The issue was fixed in Snapshot #7634339, but it introduced another bug:

Flows collected in compose screens via rememberFlowWithLifecycle(flow).collectAsState(initial) complete early on tab reselection, like in the original issue. About rememberFlowWithLifecycle

Attaching the minimal sample that shows the problem and a video.

In sample view model, there is a simple flow that emits text in some interval.

In 2.4.0-alpha04 - Collecting flows directly via collectAsState or via rememberFlowWithLifecycle works as expected (interval Flow doesn't complete until the user leaves the screen)

In 2.4.0-alpha05-06 - Screen becomes empty on tab reselection

In Snapshot #7634339 / 2.4.0-alpha07:

Tab reselection doesn't cause empty screens
Tab reselection doesn't cause early flow completion when collecting interval flow directly via collectAsState
Tab reselection does cause early flow completion when collecting interval flow wrapped in rememberFlowWithLifecycle

Comments

yu...@gmail.com <yu...@gmail.com> #2Aug 18, 2021 03:16AM

Nested scrolling works partially (as per

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

screen-20210812-232537.mp4

32 MB

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NavigationComposeBug-Flows.zip

1.6 MB

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il...@google.com <il...@google.com> #3Sep 20, 2021 11:52PM

Assigned to jb...@google.com.

Hi!

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

il...@google.com <il...@google.com> #4Sep 28, 2021 09:35PM

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

ap...@google.com <ap...@google.com> #5Oct 4, 2021 09:09PM

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> #6Oct 5, 2021 04:40PM

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.

yu...@gmail.com <yu...@gmail.com> #7Oct 5, 2021 07:38PM

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

yu...@gmail.com <yu...@gmail.com> #8Oct 5, 2021 08:50PM

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

yu...@gmail.com <yu...@gmail.com> #9Oct 6, 2021 01:05AM

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 :)