JetpackCompose 导航嵌套图导致“ViewModelStore 应在 setGraph 调用之前设置”异常

Question

我正在尝试将 Jetpack Compose 导航应用到我的应用程序中。

我的屏幕：登录/注册屏幕和底部导航栏屏幕（呼叫、聊天、设置）。

我已经发现最好的方法是使用嵌套图。

但我不断遇到ViewModelStore should be set before setGraph call例外。但是，我认为这不是正确的例外。

我的导航已经是最新版本了。可能我的嵌套图逻辑不正确。

要求：我希望能够从登录或注册屏幕导航到任何底部栏屏幕并反向导航

@Composable
fun SetupNavGraph(
    navController: NavHostController,
    userViewModel: UserViewModel
) {
    NavHost(
        navController = navController,
        startDestination = BOTTOM_BAR_GRAPH_ROUTE,
        route = ROOT_GRAPH_ROUTE
    ) {
        loginNavGraph(navController = navController, userViewModel)
        bottomBarNavGraph(navController = navController, userViewModel)
    }
}

导航图.kt

fun NavGraphBuilder.loginNavGraph(
    navController: NavHostController,
    userViewModel: UserViewModel
) {
    navigation(
        startDestination = Screen.LoginScreen.route,
        route = LOGIN_GRAPH_ROUTE
    ) {
        composable(
            route = Screen.LoginScreen.route,
            content = {
                LoginScreen(
                    navController = navController,
                    loginViewModel = userViewModel
                )
            })
        composable(
            route = Screen.RegisterScreen.route,
            content = {
                RegisterScreen(
                    navController = navController,
                    loginViewModel = userViewModel
                )
            })
    }
}

LoginNavGraph.kt

fun NavGraphBuilder.bottomBarNavGraph(
    navController: NavHostController,
    userViewModel: UserViewModel
) {
    navigation(
        startDestination = Screen.AppScaffold.route,
        route = BOTTOM_BAR_GRAPH_ROUTE
    ) {
        composable(
            route = Screen.AppScaffold.route,
            content = {
                AppScaffold(
                    navController = navController,
                    userViewModel = userViewModel
                )
            })
    }
}

BottomBarNavGraph.kt

@Composable
fun AppScaffold(
    navController: NavHostController,
    userViewModel: UserViewModel
) {
    val scaffoldState = rememberScaffoldState()

    Scaffold(

        bottomBar = {
            BottomBar(mainNavController = navController)
        },
        scaffoldState = scaffoldState,

        ) {

        NavHost(
            navController = navController,
            startDestination = NavigationScreen.EmergencyCallScreen.route
        ) {
            composable(NavigationScreen.EmergencyCallScreen.route) {
                EmergencyCallScreen(
                    navController = navController,
                    loginViewModel = userViewModel
                )
            }
            composable(NavigationScreen.ChatScreen.route) { ChatScreen() }
            composable(NavigationScreen.SettingsScreen.route) {
                SettingsScreen(
                    navController = navController,
                    loginViewModel = userViewModel
                )
            }
        }
    }
}

AppScaffold.kt

@Composable
fun BottomBar(mainNavController: NavHostController) {

    val items = listOf(
        NavigationScreen.EmergencyCallScreen,
        NavigationScreen.ChatScreen,
        NavigationScreen.SettingsScreen,
    )

    BottomNavigation(
        elevation = 5.dp,
    ) {
        val navBackStackEntry by mainNavController.currentBackStackEntryAsState()
        val currentRoute = navBackStackEntry?.destination?.route
        items.map {
            BottomNavigationItem(
                icon = {
                    Icon(
                        painter = painterResource(id = it.icon),
                        contentDescription = it.title
                    )
                },
                label = {
                    Text(
                        text = it.title
                    )
                },
                selected = currentRoute == it.route,
                selectedContentColor = Color.White,
                unselectedContentColor = Color.White.copy(alpha = 0.4f),
                onClick = {
                    mainNavController.navigate(it.route) {
                        mainNavController.graph.startDestinationRoute?.let { route ->
                            popUpTo(route) {
                                saveState = true
                            }
                        }
                        restoreState = true
                        launchSingleTop = true
                    }
                },

                )
        }

    }
}

底部栏.kt

const val ROOT_GRAPH_ROUTE = "root"
const val LOGIN_GRAPH_ROUTE = "login_register"
const val BOTTOM_BAR_GRAPH_ROUTE = "bottom_bar"

sealed class Screen(val route: String) {
    object LoginScreen : Screen("login_screen")
    object RegisterScreen : Screen("register_screen")
    object AppScaffold : Screen("app_scaffold")

}

屏幕.kt

sealed class NavigationScreen(val route: String, val title: String, @DrawableRes val icon: Int) {
    object EmergencyCallScreen : NavigationScreen(
        route = "emergency_call_screen",
        title = "Emergency Call",
        icon = R.drawable.ic_phone
    )

    object ChatScreen :
        NavigationScreen(
            route = "chat_screen",
            title = "Chat",
            icon = R.drawable.ic_chat)

    object SettingsScreen : NavigationScreen(
        route = "settings_screen",
        title = "Settings",
        icon = R.drawable.ic_settings
    )
}

导航屏幕.kt

Answer 1

在解决这个问题一段时间后，我通过使用两个独立的 NavHost 解决了这个问题。这可能不是正确的方法，但目前可行。您可以在这里找到示例源代码：

https://github.com/talhaoz/JetPackCompose-LoginAndBottomBar

希望他们能让即将发布的版本的导航变得更容易。