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

Project: platform/frameworks/support
Branch: androidx-main

commit ff83342e064a03ea410b31f825786c28d009354f
Author: Jeremy Woods <jbwoods@google.com>
Date: Tue Nov 16 08:17:07 2021

Allow nullable boolean array in safe args

While you should not be able to give a boolean a default value of null
you should be able to make an array default to null. We need to enable
safe args to generate boolean array with nullable values.

RelNote: "Fixed a bug in safe args that would not allow boolean arrays
to have a `null` value."
Test: modified NavParserTest
Bug: 174787525

Change-Id: I8c396c8f174d5924bb5ee147261de158256fba94

M navigation/navigation-safe-args-generator/src/test/test-data/naive_test.xml
M navigation/navigation-safe-args-generator/src/main/kotlin/androidx/navigation/safe/args/generator/Types.kt
M navigation/navigation-safe-args-generator/src/test/kotlin/androidx/navigation/safe/args/generator/NavParserTest.kt

https://android-review.googlesource.com/1893757

screen-20210812-232537.mp4

32 MB

Download

NavigationComposeBug-Flows.zip

1.6 MB

Download

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

Assigned to jb...@google.com.

This has been fixed internally and will be available in the next Navigation release. You can try it out now by following the snapshot instructions and using buildID #7920634.

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

We need to ensure that singleTop operations (like this) give us a NavBackStackEntry that is not .equals() to the old entry. This ensures that Compose won't skip updating the LocalLifecycleOwner.current value in this case.

This has a couple of (internal only) implications to make sure that our internal state is consistent:

We need to fix NavController's call to navigator.onLaunchSingleTop() to ensure that the new entry is added to our child/parent Lifecycle tracking maps
Ensure that we don't clear ViewModels associated with singleTop operations (i.e., validate that the same entry ID isn't on the back stack)
Update the default implementation of NavigatorState.onLaunchSingleTop to update the value as a single atomic operation (which is now possible since the entries aren't .equals() to one another)
Look at how TestNavigatorState treats reference equality to make sure it still clears/saves state properly

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

Project: platform/frameworks/support
Branch: androidx-main

commit 8ed73a2b43c94f0a1deaf12ab13e5161c2fab5cf
Author: Jeremy Woods <jbwoods@google.com>
Date: Tue Sep 28 18:09:48 2021

Modify NavBackStackEntry equality

Including the Lifecycle and SavedStateRegistry in the NavBackStackEntry
equals and hashcode functions. This will fix our issues in compose where
different instances of NavBackStackEntry were considered the same and we
were not recomposing properly.

This change always required the following:

Ensuring that ViewModels are not cleared during singleTop operations
Making sure markTransitionComplete clears all entries with the same ID
Ensure when NavController calls onSingleTop we update the links between
child and parents

We also made onLaunchSingleTop in NavigatorState a single atomic
operation to remove the old entry and add the new one.

RelNote: "NavBackStackEntries now with different Lifecycles are not
longer considered equal. This means NavHost will properly recompose all
destinations when doing navigation with singleTop and when reselecting
bottom menu items."
Bug: 196997433
Test: Added tests

Change-Id: I1b3510b238d3c4e6ed5cc86a6fddf795bd9acb02

M navigation/navigation-common/src/main/java/androidx/navigation/NavigatorState.kt
M navigation/navigation-runtime/src/androidTest/java/androidx/navigation/NavBackStackEntryTest.kt
M navigation/navigation-testing/src/androidTest/java/androidx/navigation/testing/TestNavigatorStateTest.kt
M navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt
M navigation/navigation-testing/src/main/java/androidx/navigation/testing/TestNavigatorState.kt
M navigation/navigation-runtime/src/androidTest/java/androidx/navigation/NavBackStackEntryLifecycleTest.kt
M navigation/navigation-common/src/main/java/androidx/navigation/NavBackStackEntry.kt

https://android-review.googlesource.com/1839538

jb...@google.com <jb...@google.com> #6Oct 5, 2021 04:40PM

Marked as fixed.

This has been fixed internally and will be available in the next Navigation release.

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

That's great! Is there Snapshot build number I can try before the release to test/use it?

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

Looks like https://androidx.dev/snapshots/builds has latest build numbers, so I will try that.

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

I tried build #7796270 and looks like the bug is gone. Thanks!