I have a Login screen and a Home screen. When I st...

# compose

[Lukasz Kalnik]

I have a Login screen and a Home screen. When I start the app, I check the login state and if the user is logged in, navigate with navController to the Home screen.

setContent {
    val navigateToHomeScreen by viewModel.navigateToHomeScreen.collectAsStateWithLifecycle()
    if (navigateToHomeScreen) {
        navController.navigate(HOME) {
            popUpTo(LOGIN) { inclusive = true }
    }
}

However when I close the app with the back button and then reopen, it crashes with

java.lang.IllegalArgumentException: Cannot navigate to shoppingSessions. Navigation graph has not been set for NavController androidx.navigation.internal.NavControllerImpl

[Nitesh Singh]

show me all code

[Lukasz Kalnik]

The rest is just the navigation graph

[Lukasz Kalnik]

NavHost(navController, startDestination = LOGIN) {
    composable(HOME) {
        HomeScreen( /* ... */)
    }

    composable(LOGIN) {
        LoginScreen( /* ... */)
    }
}

It uses the same navController instance, which is remembered beforehand.

[Lukasz Kalnik]

This must be some race condition, because the navigation takes place before the nav graph got composed.

[Lukasz Kalnik]

I tried wrapping the navigation in a SideEffect, but then it doesn't navigate at all.

[Nitesh Singh]

You need to make sure you are setting the navigation graph to your NavController before navigating anywhere.

[Nitesh Singh]

Ensure that your NavHost is set before you trigger any navigation

[Nitesh Singh]

val navController = rememberNavController()

NavHost(
navController = navController,
startDestination = "home", // or your actual start
) {
composable("home") { HomeScreen(navController) }
composable("shoppingSessions") { ShoppingSessionScreen() }
}

[Nitesh Singh]

Then in your composable, do
navController.navigate("shoppingSessions")

[Nitesh Singh]

Make sure you don’t call navigate() before NavHost is rendered

[Nitesh Singh]

Are you navigating after the composition lifecycle?

[Lukasz Kalnik]

How do I make sure of it?

[Lukasz Kalnik]

Note however, then I don't navigate inside the composable

[Lukasz Kalnik]

The navigation is outside of NavHost, it just reacts to a viewModel uiState change

[Lukasz Kalnik]

setContent {
    val navController = rememberNavController()

    val navigateToHomeScreen by viewModel.navigateToHomeScreen.collectAsStateWithLifecycle()

    if (navigateToHomeScreen) {
        viewModel.onNavigatedToHomeScreen() // resets the state
        navController.navigate(HOME) {
            popUpTo(LOGIN) { inclusive = true }
        }
    }

    NavHost(navController, startDestination = LOGIN) {
        composable(HOME) {
            HomeScreen( /* ... */)
        }

        composable(LOGIN) {
            LoginScreen( /* ... */)
        }
    }
}

[Nitesh Singh]

setContent {
val navController = rememberNavController()

val navigateToHomeScreen by viewModel.navigateToHomeScreen.collectAsStateWithLifecycle()

if (navigateToHomeScreen) {
viewModel.onNavigatedToHomeScreen() // resets the state
navController.navigate(HOME) {
popUpTo(LOGIN) { inclusive = true }
}
}

NavHost(navController, startDestination = LOGIN) {
composable(HOME) {
HomeScreen( /* ... */)
}

composable(LOGIN) {
LoginScreen( /* ... */)
}
}
}
all code is in same file ?

[Lukasz Kalnik]

Yes

[Lukasz Kalnik]

It's the setContent Method

[Lukasz Kalnik]

Inside the Activity's onCreate()

[Nitesh Singh]

could you tell me where the Navigation graph ?

[Lukasz Kalnik]

It's in the code

[Nitesh Singh]

before NavHost you are doing to navigate() that why you are getting error

[Nitesh Singh]

val navController = rememberNavController()
after navcontroller use navHost whereas you are using to navigate(HOME)

[Lukasz Kalnik]

Thank you, looks like it helped!

[Lukasz Kalnik]

However now it opens a new screen on top of the old one every time. Maybe you know how to fix it as well?

[Lukasz Kalnik]

launchSingleTop = true inside the navigate() didn't help

[Nitesh Singh]

navigate() issue fixed ?

[Lukasz Kalnik]

Yes

[Nitesh Singh]

popUpTo("shoppingSessions") {
inclusive = true
}

[Nitesh Singh]

use this code instant of launchSingleTop = true

[Lukasz Kalnik]

Then the login screen shows when navigating back

[Nitesh Singh]

also use this code
launchSingleTop = true

[Lukasz Kalnik]

It doesn't change anything, the login screen is still shown

[Lukasz Kalnik]

I have to

popUpTo(LOGIN) { inclusive = true }

[Nitesh Singh]

show me clear issue

[Lukasz Kalnik]

The issue is that when navigating back from shopping sessions (home) the login is shown

[Nitesh Singh]

i didn't understand about new screen or login screen

[Lukasz Kalnik]

When the user navigates with the back button

[Lukasz Kalnik]

There is login screen, and there is home (shopping sessions) screen

[Lukasz Kalnik]

When the automatic login in viewModel is successful, the shopping sessions should be shown automatically.

[Lukasz Kalnik]

But when the user then navigates with the back button from the shopping sessions screen, then the login screen should not be shown anymore

[Nitesh Singh]

so you should show login screen after back button ?

[Lukasz Kalnik]

No

[Lukasz Kalnik]

It should be removed from the back stack

[Nitesh Singh]

show me your
navigate("shoppingSessions") code

[Nitesh Singh]

after login you are going to shopping page . use below code
navController.navigate("shoppingSessions") {
popUpTo("login") {
inclusive = true // This removes login from back stack
}
launchSingleTop = true
}

[Nitesh Singh]

replace your code

[Lukasz Kalnik]

if (navigateToShoppingSessions) {
    homeViewModel.onNavigatedToShoppingSessions()
    navController.navigate(NAV_DESTINATION_SHOPPING_SESSIONS) {
        popUpTo(NAV_DESTINATION_AUTO_LOGIN) { inclusive = true }
    }
}

[Nitesh Singh]

popUpTo("login") {
inclusive = true // This removes login from back stack
this will remove your backstack or login

[Lukasz Kalnik]

That's what I already do

[Lukasz Kalnik]

Yes

[Lukasz Kalnik]

But then the shopping sessions is opened multiple times

[Nitesh Singh]

okay "NAV_DESTINATION_AUTO_LOGIN" type manualy

[Nitesh Singh]

don't use const variable

[Lukasz Kalnik]

It doesn't matter 🙂

[Nitesh Singh]

try

[Lukasz Kalnik]

You can use variables, they don't change the code behavior 🙂

[Nitesh Singh]

also use this code you are missing
launchSingleTop = true

[Lukasz Kalnik]

I already used it, it didn't help

[Lukasz Kalnik]

Still the screen opened multiple times

[Nitesh Singh]

navController.graph.startDestinationId
use this code in popUpTo()

[Nitesh Singh]

use LaunchedEffect

[Nitesh Singh]

you didn't using launchedEffect

[Lukasz Kalnik]

It also doesn't help

[Lukasz Kalnik]

LaunchedEffect(navigateToShoppingSessions) {
                if (navigateToShoppingSessions && navController.currentDestination?.route != NAV_DESTINATION_SHOPPING_SESSIONS) {
                    homeViewModel.onNavigatedToShoppingSessions()
                    navController.navigate(NAV_DESTINATION_SHOPPING_SESSIONS) {
                        popUpTo(navController.graph.startDestinationId) { inclusive = true }
                        launchSingleTop = true
                    }
                }
            }

[Lukasz Kalnik]

Still opens the shopping sessions screen multiple times

[Nitesh Singh]

val hasNavigated = remember { mutableStateOf(false) }
LaunchedEffect(navigateToShoppingSessions) {
if (navigateToShoppingSessions && !hasNavigated.value) {
hasNavigated.value = true
homeViewModel.onNavigatedToShoppingSessions()
navController.navigate(NAV_DESTINATION_SHOPPING_SESSIONS) {
popUpTo(navController.graph.startDestinationId) {
inclusive = true
}
launchSingleTop = true
}
}
}

use above code

[Nitesh Singh]

have you try ? if fix let me know

[Lukasz Kalnik]

It doesn't change anything

[Lukasz Kalnik]

Thank you for your help

[Lukasz Kalnik]

I will figure it out by myself

[Nitesh Singh]

could you show me login candition ?

[Lukasz Kalnik]

Thank you for your help!

[Nitesh Singh]

okay if you want help reach out to me

[Lukasz Kalnik]

So the problem was that the HomeActivity was missing the launchMode:singleTop in manifest