Dagger support


Dagger 2 is RainbowCake’s primary dependency injection solution, via the rainbow-cake-dagger artifact which makes it easy to get started with the framework.

For a starter project that already has Dagger 2 set up for use with RainbowCake, check out Blank.

See the Dependency Injection page for more details about dependency injection in RainbowCake in general.

Providing dependencies

For the injection mechanism to know about your ViewModels, they have to be declared in a Dagger module, conventionally named ViewModelModule, and placed in a di package within the app’s root package:

abstract class ViewModelModule {
    abstract fun bindMainViewModel(mainViewModel: MainViewModel): ViewModel
    abstract fun bindUserViewModel(userViewModel: UserViewModel): ViewModel

Each binding requires an abstract function that takes the given specific ViewModel as a parameter, and is annotated with @ViewModelKey, with the same ViewModel class specified in the annotation as the key. Their return type always has to be the base ViewModel type.

To learn more about this setup, see the implementation details.

The constructors of your ViewModels should be annotated with @Inject so that Dagger knows how to create them:

class UserViewModel @Inject constructor(
    private val userPresenter: UserPresenter
): RainbowCakeViewModel<UserViewState>(Loading) {
    // ...

For the other classes that your ViewModels or lower layers depend on, you should also annotate their constructors with @Inject:

class UserPresenter @Inject constructor() {
    suspend fun getUser(): User = withIOContext { /* ... */ }

This is just the very basics of a Dagger setup, you can also declare additional modules with dependencies, etc. See the Dagger documentation for more details.

Component setup

RainbowCake’s Dagger integration works with a single application level component with a @Singleton scope to create ViewModels.

This means that you’ll have to create a Dagger component that contains ViewModelModule as well as the RainbowCakeModule that comes from the rainbow-cake-dagger artifact. Your component needs to extend RainbowCakeComponent:

    modules = [
interface AppComponent : RainbowCakeComponent

Application class setup

Finally, you’ll need an Application implementation class that extends RainbowCakeApplication. This will override the injector property with the type of the concrete Dagger component that will be used in the application, in this example, AppComponent. The setupInjector method also needs to be overridden appropriately - it should create and assign an instance of the component:

class MyApplication : RainbowCakeApplication() {

    override lateinit var injector: AppComponent

    override fun setupInjector() {
        injector = DaggerAppComponent.create()


Make sure you set this application up in your AndroidManifest.xml file as well, in your application tag’s name property.