我正在尝试在viewModel中使用Jetpack Compose导航。当触发导航时，没有任何反应。这是我的方法：
我定义了NavigationDestination。在我的情况下，我有四个屏幕：欢迎、登录、注册和调查。
interface NavigationDestination {
val route: String
}
sealed class Screen(override val route: String) : NavigationDestination {
object WelcomeScreen : Screen("welcome")
object SignInScreen : Screen("signIn")
object SignUpScreen : Screen("signUp")
object SurveyScreen : Screen("survey")
}
Navigator是一个与默认屏幕WelcomeScreen一起使用的工具，它可以展示当前的目标位置。
class Navigator {
var destination: MutableStateFlow<NavigationDestination> = MutableStateFlow(Screen.WelcomeScreen)
fun navigate(destination: NavigationDestination) {
this.destination.value = destination
}
}
在主组合中，我获取 NavHostController 并监听 Navigator 的变化。
@Composable
fun JetSurvey0App() {
val welcomeViewModel: WelcomeViewModel = viewModel(factory = WelcomeViewModelFactory())
val navigator = Navigator()
val navController = rememberNavController()
val destination by navigator.destination.collectAsState()
LaunchedEffect(destination) {
if (navController.currentDestination?.route != destination.route) {
navController.navigate(destination.route)
}
}
NavHost(navController = navController, startDestination = navigator.destination.value.route) {
composable(Screen.WelcomeScreen.route) {
WelcomeScreen(
onEvent = { event ->
when (event) {
is WelcomeEvent.SignInSignUp -> welcomeViewModel.handleContinue(event.email)
WelcomeEvent.SignInAsGuest -> welcomeViewModel.signInAsGuest()
}
}
)
}
composable(Screen.SignUpScreen.route) {
SignUp()
}
composable(Screen.SignInScreen.route) {
SignIn()
}
composable(Screen.SurveyScreen.route) {
SurveyQuestionsScreen()
}
}
}
在WelcomeViewModel中，我通过调用Navigator来执行解耦导航，如下所示。
class WelcomeViewModel(
private val userRepository: UserRepository,
private val navigator: Navigator
) : ViewModel() {
fun handleContinue(email: String) {
if (userRepository.isKnownUserEmail(email)) {
viewModelScope.launch {
navigator.navigate(Screen.SignInScreen)
}
} else {
viewModelScope.launch {
navigator.navigate(Screen.SignUpScreen)
}
}
}
fun signInAsGuest() {
viewModelScope.launch {
navigator.navigate(Screen.SurveyScreen)
}
userRepository.signInAsGuest()
}
}
class WelcomeViewModelFactory : ViewModelProvider.Factory {
@Suppress("UNCHECKED_CAST")
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(WelcomeViewModel::class.java)) {
return WelcomeViewModel(UserRepository, Navigator()) as T
}
throw IllegalArgumentException("Unknown ViewModel class")
}
}