ViewModels

SavedStateHandle injection

Tangle supports injecting SavedStateHandle into ViewModel constructors, where the SavedStateHandle is provided by the ViewModel's owning Fragment/Activity /NavBackStackEntry.

In addition to or in lieu of SavedStateHandle, Tangle can automatically extract arguments from the SavedStateHandle and inject them into the constructor, through use of the FromSavedStateHandle annotation.

If the constructor argument's type is not nullable, then Tangle will assert that the argument is in the bundle while creating the ViewModel.

If the argument is marked as nullable, then Tangle will gracefully handle a missing argument and just inject null.

Given this code:

class MyViewModel @VMInject constructor(
  @FromSavedState("userId")
  val userId: String,
  @FromSavedState("address")
  val addressOrNull: String?
) : ViewModel()

Tangle will generate this Provider:

public class MyViewModel_Provider @Inject constructor(
  private val savedStateHandle: Provider<SavedStateHandle>
) : Provider<MyViewModel> {
  public override fun `get`(): MyViewModel {
    val userId = savedStateHandle.get().get<String>("userId")
    checkNotNull(userId) {
      "Required parameter with name `userId` " +
      "and type `kotlin.String` is missing from SavedStateHandle."
    }
    val addressOrNull = savedStateHandle.get().get<String?>("address")
    return MyViewModel(userId, addressOrNull, savedStateHandle.get())
  }
}

Compose support

Tangle supports ViewModel "injection" in composables in a manner very similar to Hilt's navigation/viewModel artifact. It will scope the ViewModel to the composable's NavBackStackEntry.

@Composable
fun MyComposable(
  navController: NavController,
  viewModel: MyViewModel = tangle()
) {
  // ...
}