SavedStateHandle on ViewModel not contain navigation argument

[CMFerrer]

I'm trying to inject SavedStateHandle. I am using jetpack compose and navigation

Here is my NavHost:

AnimatedNavHost(
    navController = navController,
    startDestination = "main_route", route = "Parent"
) {
     composable(
        route = "main_route",
        enterTransition = {...},
        exitTransition = {...}
    )
    {
        MainScreen()
     }

    composable(
        route = "route_A/{text}",
        arguments = listOf(navArgument(name = "text") {
            type = NavType.BoolType

        }),
        enterTransition = {...},
        exitTransition = {...}
    )
    {
        val parentEntry = remember(it) { navController.getBackStackEntry("Parent") }
        val sharedViewModel = hiltViewModel<SharedViewModel>(parentEntry)
        val state by sharedViewModel.stateA.collectAsStateWithLifecycle()

        CaloScreen(
            state,
            ) { navigate ->
                navController.navigate(route = "route_detail/$navigate")
            }
     }

    composable(
        route = "route_B/{text}",
        arguments = listOf(navArgument(name = "text") {
            type = NavType.BoolType

        }),
        enterTransition = {...},
        exitTransition = {...}
    )
    {
        val parentEntry = remember(it) { navController.getBackStackEntry("Parent") }
        val sharedViewModel = hiltViewModel<SharedViewModel>(parentEntry)
        val state by sharedViewModel.stateB.collectAsStateWithLifecycle()

        CaloScreen(
            state,
            ) { navigate ->
                navController.navigate(route = "route_detail/$navigate")
            }
     }

    composable(
        route = "route_detail/{id}",
        arguments = listOf(navArgument(name = "id") {
            type = NavType.StringType

        })
    )
    {
        val detailViewModel = hiltViewModel<DetailViewModel>()
        val state by detailViewModel.state.collectAsStateWithLifecycle()

        DeloScreen(state)
    }
}

Here is SharedViewModel:

@HiltViewModel
class SharedViewModel @Inject constructor(
    savedStateHandle: SavedStateHandle,
    private val repo: DataRepository
) : ViewModel() {

    private val _stateA = MutableStateFlow(value = CaloState())
    val stateA = _stateA.asStateFlow()

    private val _stateB = MutableStateFlow(value = CaloState())
    val stateB = _stateB.asStateFlow()

    init {
        val argument = savedStateHandle.get<Boolean>("text")
        ...
        ...
    }
    ...
}

savedStateHandle always return null, not contain any keys. This happens in the SharedViewModel but not in the detailviewmodel. When I don't pass the parentEntry to the sharedviewmodel of route_A and route_B it returns the value passed by argument but they would no longer share the same ViewModel instance.
I also tried to make the argument a String type but it didn't work anyway.

Hilt version use -> 2.44.2

I'm new to Android, thanks in advance

[kuanyingchou]

Hi, @CMFerrer , thanks for reporting. It seems that navigation is also using the same underlying mechanism to implement their nav arguments, and here your're trying to write the text arg in navigation and read it in a viewmodel. This behavior is probably not something you want to depend on. For now it may be better to also read the nav arg in navigation with NavBackStackEntry#arguments and pass that to the viewmodel after the hiltViewModel() call. We're still working on the feature to pass something manually to hiltViewModel() so it should get better in the future.

[kuanyingchou]

Sorry I just found that passing data though navArgs and reading them from savedStateHandle in ViewModels is what Navigation recommends. Please ignore my comment above. However, reading the navArgs in a ViewModel that's scoped to Parent is not going to work as the args are stored separately. This is a Navigation issue instead of a Hilt issue. For example, remove Hilt from the scene and replace hiltViewModel() with androidx.lifecycle.viewmodel.compose.viewModel() and the issue remains. In this case you may have to wire the data manually.