IssueTracker

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.

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

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:

1. Navigate from Second Fragment to Child nav graph (with non-nullable parameters).
2. 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.

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.

This has been fixed and will be available in navigation 2.6.0-alpha08

The following release(s) address this bug.It is possible this bug has only been partially addressed:

• androidx.navigation:navigation-runtime:2.6.0-alpha08

The issue is inside NavHost.

        val modifier = Modifier.padding(padding)
        NavHost(navController, startDestination = FIRST_SCREEN) {
            composable(FIRST_SCREEN) {
                MyScreen(modifier, Color.Blue) {
                    navController.navigate(SECOND_SCREEN)
                }
            }
            composable(SECOND_SCREEN) {
                MyScreen(modifier, Color.Red) {
                    navController.navigate(FIRST_SCREEN)
                }
            }
        }

When the size has been changed the first line is recomposed and the new modifier object is constructed. Then NavHost is reinvoked with a new builder which contains new lambdas which captures a new modifier. But currently NavHost is not supporting nav graph updates so the new lambdas are ignored. As a result we end up using the initial value of the captured modifier object forever which had size 0. The current workaround would be something like

        val modifier = rememberUpdatedState(Modifier.padding(padding))
        NavHost(navController, startDestination = FIRST_SCREEN) {
            composable(FIRST_SCREEN) {
                MyScreen(modifier.value, Color.Blue) {
                    navController.navigate(SECOND_SCREEN)
                }
            }
            composable(SECOND_SCREEN) {
                MyScreen(modifier.value, Color.Red) {
                    navController.navigate(FIRST_SCREEN)
                }
            }
        }

In this case we wrap the value inside the state object so we can update the state and the old lambda would still use the correct modifier.

Jeremy, assigning it to you as the only correct solution is to support graph updates

So I believe this is related to this as well right?

https://kotlinlang.slack.com/archives/CJLTWPH7S/p1614342645375500

oh sorry about that i linked the wrong thread..

https://kotlinlang.slack.com/archives/CJLTWPH7S/p1610188317341100

its this instead..

Alright. I guess this would hit two issues at the same time then. Thank you!

Note that if you want to pad in all screens, you should passing the padding directly to NavHost rather than manually to each screen:

) { padding ->
        NavHost(navController, startDestination = FIRST_SCREEN, Modifier.padding(padding)) {
            composable(FIRST_SCREEN) {
                MyScreen(Color.Blue) {
                    navController.navigate(SECOND_SCREEN)
                }
            }
            composable(SECOND_SCREEN) {
                MyScreen(Color.Red) {
                    navController.navigate(FIRST_SCREEN)
                }
            }
        }
    }
}

This was made possible in b/175125483 and was part of Navigation Compose 1.0.0-alpha10.

This has been fixed internally and will be part of the Navigation 2.4.0-alpha05 release.