AssistedInject ViewModel helpers

[steurt]

I came across the blog post Providing AssistedInject supported ViewModel for Composable using Hilt through Android Weekly. Coincidentally I was just about to see how I could make AssistedInject work alongside Hilt and Compose. The post therefore was very helpful!

I applied the described setup and extended on it a little by adding some helpers to make the setup a bit more generic with a bit less boilerplate code.

I added the AssistedViewModel.kt file:

/**
 * Returns an existing [AssistedInject]-annotated [ViewModel] or creates a new one based on the
 * current view model store owner.
 */
@Composable
inline fun <reified VM : ViewModel> assistedViewModel(
    viewModelStoreOwner: ViewModelStoreOwner = checkNotNull(LocalViewModelStoreOwner.current) {
        "No ViewModelStoreOwner was provided via LocalViewModelStoreOwner"
    },
    provideFactory: AssistedViewModelFactoryProvider.() -> ViewModelProvider.Factory,
): VM {
    val factory = provideFactory(assistedViewModelFactory())
    return viewModel(viewModelStoreOwner, factory = factory)
}

/**
 * Returns the [AssistedViewModelFactoryProvider] of the activity from the current [LocalContext].
 */
@Composable
fun assistedViewModelFactory() = EntryPointAccessors.fromActivity(
    LocalContext.current as Activity,
    AssistedViewModelFactoryProvider::class.java
)

With these helpers in this case the fun noteDetailViewModel can be removed. The helpers can now simply be used as follows:

NavHost(navController, startDestination = Screen.Notes.route, route = NOTY_NAV_HOST_ROUTE) {
    composable(
        Screen.NotesDetail.route,
        arguments = listOf(navArgument(Screen.NotesDetail.ARG_NOTE_ID) { type = NavType.StringType })
    ) {
        val noteId = requireNotNull(it.arguments?.getString(Screen.NotesDetail.ARG_NOTE_ID))
        val viewModel = assistedViewModel<NoteDetailViewModel> {
            provideFactory(noteDetailViewModelFactory(), noteId = noteId)
        }
        NoteDetailsScreen(navController, viewModel)
    }
}

What do you think of this setup?

[PatilShreyas]

@steurt this structure really looks good and clean too.