如何在底部导航 Jetpack Compose 中保存嵌套导航图 id 的目的地？

Question

I am facing some problems with navigation's back stacks in Jetpack Compose. The following diagram is my desired scenario.

I have bottom bar and two items Home and Setting. And I want to make both as nested graphs. In HomeNavGraph, HomeRootScreen is startDestination and can navigate to HomeDetail1Screen and HomeDetail2. Setting tab also likes that. And I want to save those nested graph states like When I click HomeRoot -> HomeDetail1 -> HomeDetail2, at that time I click Setting tab in BottomBar. And click back to Home, I want my current Screen to HomeDeatil2Screen.

The followings are my codes. This is my Destination class.

    sealed class Destinations(
    val route: String
) {
    object HomeRoot : Destinations(route = "home_root_screen")
    object HomeDetail1 : Destinations(route = "home_detail1_screen")
    object HomeDetail2 : Destinations(route = "home_detail2_screen")

    object SettingRoot : Destinations(route = "setting_root_screen")
    object SettingDetail1 : Destinations(route = "setting_detail1_screen")
    object SettingDetail2 : Destinations(route = "setting_detail2_screen")
}

const val BOTTOM_NAV_ROUTE = "btn_nav"
const val HOME_ROUTE = "home"
const val SETTING_ROUTE = "setting"

This is my BottomBarNavGraph.

@Composable
fun BottomBarNavGraph(
    navController: NavHostController
) {
    NavHost(
        navController = navController,
        startDestination = HOME_ROUTE,
        route = BOTTOM_NAV_ROUTE
    ) {
        homeNavGraph(navController)
        settingNavGraph(navController)
    }
}

This is HomeNavGraph.

fun NavGraphBuilder.homeNavGraph(
    navController: NavHostController
) {
    navigation(
        startDestination = Destinations.HomeRoot.route,
        route = HOME_ROUTE
    ) {
        composable(route = Destinations.HomeRoot.route) { HomeScreen(navController = navController) }
        composable(route = Destinations.HomeDetail1.route + "/{argText}") {
            val arg = it.arguments?.getString("argText") ?: "Nothing Typed"
            HomeDetail1Screen(
                text = arg,
                navController = navController
            )
        }
        composable(route = Destinations.HomeDetail2.route) { HomeDetail2Screen(navController = navController) }
    }
}

This is SettingNavGraph.

fun NavGraphBuilder.settingNavGraph(
    navController: NavHostController
) {
    navigation(
        startDestination = Destinations.SettingRoot.route,
        route = SETTING_ROUTE
    ) {
        composable(
            route = Destinations.SettingRoot.route
        ) {
            SettingScreen(navController = navController)
        }
        composable(
            route = Destinations.SettingDetail1.route
        ) {
            SettingDetail1Screen(navController = navController)
        }
        composable(
            route = Destinations.SettingDetail2.route
        ) {
            SettingDetail2Screen(navController = navController)
        }
    }

}

This is my BottomBarDestinations.

sealed class BottomBarDestinations(
    val route: String,
    val title: String,
    val icon: ImageVector

) {
    object Home : BottomBarDestinations(
        route = HOME_ROUTE,
        title = "Home",
        icon = Icons.Default.Home
    )

    object Setting : BottomBarDestinations(
        route = SETTING_ROUTE,
        title = "Setting",
        icon = Icons.Default.Settings
    )
}

The followings are my setup of BottomBar in navHost.

@Composable
fun BottomBar(navController: NavHostController) {
    val screens = listOf(
        BottomBarDestinations.Home,
        BottomBarDestinations.Setting
    )
    val navBackStackEntry by navController.currentBackStackEntryAsState()
    val currentDestinations = navBackStackEntry?.destination

    BottomNavigation {
        screens.forEach {
            AddItem(
                screen = it,
                currentDestinations = currentDestinations,
                navController = navController
            )
        }
    }
}

@Composable
fun RowScope.AddItem(
    screen: BottomBarDestinations,
    currentDestinations: NavDestination?,
    navController: NavHostController
) {
    BottomNavigationItem(
        label = {
            Text(text = screen.title)
        },
        icon = {
            Icon(
                imageVector = screen.icon,
                contentDescription = "Nav Icon"
            )
        },
        selected = currentDestinations?.hierarchy?.any { it.route == screen.route } == true,
        unselectedContentColor = LocalContentColor.current.copy(
            alpha = ContentAlpha.disabled
        ),
        onClick = {
            navController.navigate(screen.route) {
                popUpTo(navController.graph.findStartDestination().id)
                launchSingleTop = true
                restoreState = true
            }
        }
    )
}

@Composable
fun MainScreen(
) {
    val navController = rememberNavController()
    Scaffold(bottomBar = {
        BottomBar(navController = navController)
    }) {
        BottomBarNavGraph(navController = navController)
    }
}

Please help me with this. I stack with this. If you want to check the source code. You can check this in branch

bottom_nav_graph

https://github.com/kyawlinnthant/JetpackComposeNavigationComponent/tree/nested_graph

Answer 1

If you need to save state of route (Screen) or graph, you need to use following technique:

navController.navigate(screen.route) {
                popUpTo(navController.graph.findStartDestination().id){
                    inclusive = true
                    saveState = true
                }
                launchSingleTop = true
                restoreState = true
            }

BTW, I can't use

navController.graph.findStartDestination().id

I specify the start destination by myself (in your case will be "home_root_screen").