Dagger Usage Sample for Mavericks

This module contains a sample app to demonstrate how to ease the usage of Dagger and AssistedInject in apps using Mavericks.

Key Features

• Injecting state into ViewModels with AssistedInject

  Since the initialState parameter is only available at runtime, we use Dagger assisted injection.

• Multibinding setup for Dagger

  Every ViewModel using Dagger assisted injection needs a Factory interface annotated with @AssistedFactory. These factories are grouped together under a common parent type AssistedViewModelFactory to enable a Multibinding Dagger setup.

• Removing boilerplate from a MavericksViewModelFactory

  An MavericksViewModelFactory is different than an AssistedInject Factory, and is still needed. Using this AssistedInject multibinding setup, most ViewModels will share the same boilerplate logic in their MavericksViewModelFactory's. A DaggerMavericksViewModelFactory has been added to eliminate this boilerplate.

Example

• Create your ViewModel with an @AssistedInject constructor, an AssistedInject Factory implementing AssistedViewModelFactory, and a companion object implementing DaggerMavericksViewModelFactory.

class MyViewModel @AssistedInject constructor(
  @Assisted initialState: MyState,
  // and other dependencies
) {

  @AssistedFactory
  interface Factory: AssistedViewModelFactory<MyViewModel, MyState> {
    override fun create(initialState: MyState): MyViewModel
  }

  companion object: DaggerMavericksViewModelFactory(MyViewModel::class.java)
}

• Tell Dagger to include your ViewModel's AssistedInject Factory in a Multibinding map.

@Module
interface AppModule {

    @Binds
    @IntoMap
    @ViewModelKey(MyViewModel::class)
    fun myViewModelFactory(factory: MyViewModel.Factory): AssistedViewModelFactory<*, *>

}

• Add a provision for the Multibinding map in your Dagger component:

    fun viewModelFactories(): Map<Class<out BaseViewModel<*>>, AssistedViewModelFactory<*, *>>

• With this setup complete, request your ViewModel in a Fragment as usual, using any of Mavericks' ViewModel delegates.

class MyFragment : Fragment(), MavericksView {
  val viewModel: MyViewModel by fragmentViewModel()
}

How it works

The DaggerMavericksViewModelFactory is used by Mavericks to create the requested ViewModel. This factory uses the map of AssistedInject factories provided in the AppComponent, retrieves the one for the requested ViewModel and delegates the creation to it.