How can be saved the destinations of nested navigation graph's id in the bottom navigation Jetpack Compose? - android-jetpack-compose

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").