使用 Jetpack Compose 导航时无法创建视图模型的实例

Question

I am using navigation component for jetpack compose in my app like this:

@Composable
fun FoodiumNavigation() {
    val navController = rememberNavController()

    NavHost(
        navController = navController,
        startDestination = Screen.Main.route,
    ) {
        composable(Screen.Main.route) {
            MainScreen(navController)
        }

        ...
    }
}

And I am getting viewmodel in my MainScreen composable like this:

@Composable
fun MainScreen(navController: NavController) {
    val mainViewModel: MainViewModel = viewModel()
    ...
}

which is giving me a runtime exception as Cannot create an instance of class com.package.main.MainViewModel .

Here, I am stating that this only happens while using navigation component, ie everything was working fine and mainViewModel was successfully instantiated before using navigation component in my app.

The MainViewModel is like this:

@ExperimentalCoroutinesApi
@HiltViewModel
class MainViewModel @Inject constructor(private val postRepository: PostRepository) :
    ViewModel() {

    private val _postsLiveDataState = MutableLiveData<UiState<List<Post>>>()
    val postLiveState: LiveData<UiState<List<Post>>> = _postsLiveDataState

    init {
        getPostsState()
    }

    private fun getPostsState() {
        viewModelScope.launch {
            postRepository.getAllPosts()
                .onStart { _postsLiveDataState.value = UiState(loading = true) }
                .map { resource -> UiState.fromResource(resource) }
                .collect { state -> _postsLiveDataState.value = state }
        }
    }
}

Answer 1

If your @HiltViewModel is scoped to the navigation graph use hiltNavGraphViewModel() instead of viewModel() to initialize. For more reference android documentaion

Answer 2

hiltNavGraphViewModel is deprecated, should be used hiltViewModel() instead

also add dependency androidx.hilt:hilt-navigation-compose:1.0.0-alpha03

Answer 3

You should add this

implementation("androidx.hilt:hilt-navigation-compose:1.0.0")

then you can use this code for create instance of your viewmodel

val viewModel: YourViewModelClass= hiltViewModel()

Answer 4

You can use viewModel() as well, but check that owning Activity or Fragment has been annotated with @AndroidEntryPoint .