NavBackStackEntry lifecycle events are not the expected after process death [155218371]

Fixed

Bug

Status Update

No update yet.

Description

kh...@gmail.com

created issue #1

Apr 29, 2020 12:58PM

Component used: Navigation Version used:2.3.0-alpha05

Devices/Android versions reproduced on: Emulator, Android 11 DP3

I'm trying out returning results from dialogFragments with the SavedStateHandle you provide in this latest versions. it works well, taking into account the "Additional Considerations" section advice, of observing the NavBackStackEntry lifecycle, so the weird stuff that happens of having the fragment and the dialog being resumed at the same time doesn't affect when we receive the result.

But, process death is problematic, first I encountered https://issuetracker.google.com/154405007 It's easy to fix once you know what's happening. But now the problem I'm seeing is that the lifecycle events do not work in the same way when process death has occurred and backstack state is restored.

Normally, what I see is this, on the currentBackStackEntry: onCreate -> onStart -> onResume -> (we open the dialog) -> onPause ... and then onResume again when we come back from the dialog. Everything is cool here.

But after process death, this happens: onCreate -> onStart -> onResume We never hit onPause, and so we never "come back" to onResume after dismissing the dialog. We will never receiver the ON_RESUME event again to get the result.

I'm not sure if this is a bug, or just a consequence of how the state restoration is done on the backstack, but it pretty much means that this https://developer.android.com/guide/navigation/navigation-programmatic#additional_considerations, won't always work.

I attach a minimal repo to reproduce this, just click on the dialog button, and on receiving a result on the first fragment a toast will appear. Now, if you go to dialog once again, leave the app, and trigger process death and return to the app, it won't work. https://github.com/MrMPN/NavEntryLifecycleMinRepo

It's not a common case I think, but given the info on the documentation, it was unexpected to see it fail like this.

Comments

il...@google.com <il...@google.com> Apr 29, 2020 06:00PM

Assigned to jb...@google.com.

ap...@google.com <ap...@google.com> #2May 6, 2020 08:27PM

Oh I forgot to mention that I thought it might be connected to this issue: https://issuetracker.google.com/issues/243778589. But after trying 2.5.2 I can say that the issue persists.

jb...@google.com <jb...@google.com> #3May 6, 2020 08:31PM

Marked as fixed.

Please provide a minimal sample project along with the minimal steps to recreate the issue in the project.

an...@google.com <an...@google.com> #4May 27, 2020 12:23AM

Sorry for the delay. I got a working example here: https://github.com/Del-S/issues. The project is set up to crash when navigating to ThirdFragment (nested nav graph) with poping the graph.

I poked into it a little bit and it seems to be connected to SafeArgs gradle plugin. When safe args is used to navigate to ThirdFragment (with nested graph poped) it will try to recreate te parent but there were no arguments passed so it crashes.

Steps to reproduce:

Navigate from Second Fragment to Child nav graph (with non-nullable parameters).
Navigate to Third fragment using SafeArgs and the app crashes.

Crash log:

Process: cz.dels.issues, PID: 1743
java.lang.NullPointerException: null cannot be cast to non-null type kotlin.Long
at androidx.navigation.NavType$Companion$LongType$1.get(NavType.kt:352)
at androidx.navigation.NavType$Companion$LongType$1.get(NavType.kt:342)
at androidx.navigation.NavArgument.verify(NavArgument.kt:76)
at androidx.navigation.NavDestination.addInDefaultArgs(NavDestination.kt:502)
at androidx.navigation.NavController.addEntryToBackStack(NavController.kt:1865)
at androidx.navigation.NavController.addEntryToBackStack$default(NavController.kt:1813)
at androidx.navigation.NavController$navigate$4.invoke(NavController.kt:1721)
at androidx.navigation.NavController$navigate$4.invoke(NavController.kt:1719)
at androidx.navigation.NavController$NavControllerNavigatorState.push(NavController.kt:287)
at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.kt:246)
at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.kt:162)
at androidx.navigation.NavController.navigateInternal(NavController.kt:260)
at androidx.navigation.NavController.navigate(NavController.kt:1719)
at androidx.navigation.NavController.navigate(NavController.kt:1545)
at androidx.navigation.NavController.navigate(NavController.kt:1472)
at androidx.navigation.NavController.navigate(NavController.kt:1930)
at cz.dels.issues.SecondFragment.onViewCreated$lambda-0(SecondFragment.kt:38)
at cz.dels.issues.SecondFragment.$r8$lambda$XDYnOS_cYrafiNQ5rcCu1WCn0IE(Unknown Source:0)
at cz.dels.issues.SecondFragment$$ExternalSyntheticLambda0.onClick(Unknown Source:2)

Note: If in step 2 SaveArgs is not used then navigation works correctly. More information is here: https://github.com/Del-S/issues/blob/master/app/src/main/java/cz/dels/issues/SecondFragment.kt#L37.

il...@google.com <il...@google.com> #5May 27, 2020 05:37PM

Ups a typo: Navigate from ~~Second~~ First Fragment to Child nav graph (with non-nullable parameters).

Note: sorry for the spam but I am not able to edit my own comment.

Issue 155218371