Find component

Let's imagine two situations:

1. Your class doesn't have its own component and needs the AppComponent to inject dependencies;
2. The builder needs some Dagger component dependencies to build the component.

---

We will start from the first situation.

For example, you have bound the AppComponent in the Application class.

class App : Application(), IHasComponent {

    override fun onCreate() {
        super.onCreate()
        XInjectionManager.instance
            .bindComponent<AppComponent>(this)
            .inject(this)
    }

    override fun createComponent(): AppComponent =
        DaggerAppComponent.builder().build()
}

And in the MainActivity you need this component, so you call the findComponent<AppComponent>() method.

class MainActivity : AppCompatActivity() {

    //...code...

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        XInjectionManager.instance.findComponent<AppComponent>().inject(this)
    }
}

Make sure, the the needed component is still alive, otherwise you will get a ComponentNotFoundException exception.

---

So now we are going to use the findComponent<AppDependencies>() method to look for the dagger component dependency.

Imagine you have an AppComponent, that implements the AppDependencies interface.

@Singleton
@Component(modules = [AppModule::class])
interface AppComponent : AppDependencies {
    fun inject(app: App)
}

@Module
class AppModule {
    @Singleton
    @Provides
    fun provideTextHolder() = TextHolder()
}

interface AppDependencies {
    fun provideSingletonTextHolder(): TextHolder
}

You have bound the AppComponent to the Application.

class App : Application(), IHasComponent {

    override fun onCreate() {
        super.onCreate()
        XInjectionManager.instance
            .bindComponent<AppComponent>(this)
            .inject(this)
    }

    override fun createComponent(): AppComponent =
        DaggerAppComponent.builder().build()
}

In the feature module, you have a FeatureAComponent that requires the AppDependencies.

@FeatureAScope
@Component(dependencies = [AppDependencies::class])
interface FeatureAComponent {
    fun inject(fragment: FragmentA)
}

Ho do we get the AppDependencies? The answer is just call the findComponent<AppDependencies>() method. InjectionManager knows about AppComponent and knows that this component implements AppDependencies interface, so it can return it to you.

class FragmentA : Fragment(), IHasComponent {

    @Inject
    lateinit var textHolder: TextHolder

    //...code...

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        XInjectionManager.instance
            .bindComponent<FeatureAComponent>(this)
            .inject(this)
    }

    override fun createComponent(): FeatureAComponent =
        DaggerFeatureAComponent.builder()
            .appDependencies(
                XInjectionManager.instance.findComponent<AppDependencies>()
            )
            .build()
}

That's it. But you need to be sure that the AppComponent is still alive.