How to get access to Arguments/Extras Bundle in ViewModel with minimal boilerplate using Dagger 2?

Question

I'm transitioning my app to use ViewModels. For instantiating the ViewModels I use a custom Factory and Dagger 2 for dependency injection. It looks like this:

@Singleton
class ViewModelFactory @Inject constructor(
    private val viewModels: Map<Class<out ViewModel>, @JvmSuppressWildcards Provider<ViewModel>>
) : ViewModelProvider.Factory {

    override fun <T : ViewModel> create(modelClass: Class<T>): T 
        = viewModels[modelClass]!!.get() as T
}

@Target(AnnotationTarget.FUNCTION) @Retention(AnnotationRetention.RUNTIME) @MapKey
annotation class ViewModelKey(val value: KClass<out ViewModel>)

@Module
abstract class ViewModelModule {

    @Binds
    abstract fun bindViewModelFactory(factory: ViewModelFactory): ViewModelProvider.Factory

    @Binds @IntoMap @ViewModelKey(FooViewModel::class)
    abstract fun fooViewModel(viewModel: FooViewModel): ViewModel
}

Now I'm facing the question, how to access the Arguments/Extras Bundle of my Fragment or Activity inside a ViewModel. This is necessary because the views and therefore the data in the ViewModel is often parametrizable. How would I implement this using the least amount of boilerplate?

Answer 1

If you use Saved State module, both activity intent extras and fragment arguments are available via SavedStateHandle

class SavedStateViewModel(private val state: SavedStateHandle) : ViewModel() {
  init {
    val someArgument = state.get<String>("someArgumentKey")
    ...
  }
}

You can also use AssistedInject library to pass arguments from an Activity/Fragment into a ViewModel, but it's a boilerplate solution. Here's a dagger example, and another one which uses dagger hilt.