How do you inject subcomponent factory

[matejdro]

Maybe a bit stupid question, but I've been trying to figure out how to actually inject the factory into something to instantiate the subcomponent:

@Component
@MergeComponent(AppScope::class)
@SingleIn(AppScope::class)
interface AppComponent : AppComponentMerged {
    fun provideRendererUsage(): RendererUsage
}

@ContributesSubcomponent(LoggedInScope::class)
@SingleIn(LoggedInScope::class)
interface RendererComponent {

    @ContributesSubcomponent.Factory(AppScope::class)
    interface Factory {
        fun createRendererComponent(argument: String): RendererComponent
    }
}

Inject
class RendererUsage(rendererComponentFactory: RendererComponent.Factory)

But above fails with Cannot find an @Inject constructor or provider for: RendererComponent.Factory

[vRallev]

AppComponent will implement the Factory interface. You cannot inject components themselves, therefore you cannot inject Factory. Simply take the AppComponent and call the createRendererComponent() function on it.

[matejdro]

That kinda breaks the non-centralised nature of Anvil, since you still need access to the component instance to create subcomponents.

Is this a fault of kotlin-inject-anvil or kotlin-inject?

[vRallev]

kotlin-inject, but it's the same in Dagger. You need the reference to the component for the parent-child relationship of the components. There's no way around it. Think of the @Factory annotation the same way as a @ContributesTo annotation.

[matejdro]

Doh, the solution is just to add a @Provides function to your main component, that points to itself, which allows injection of it anywhere.

   @Provides
   fun provideRendererSubcomponentFactory(): RendererComponent.Factory = this

do you think it would be a good idea to add this to the README? I can make a PR if necessary.

but it's the same in Dagger

I'm pretty sure that with Dagger's Anvil, you can directly inject subcomponent factories.

[vRallev]

To be honest, I never tried this 🙃 Instead of updating the README, this function should be generated.

[matejdro]

Thank you!