Class Factory¶

Table of Contents¶

Overview
Creating a factory
Annotating interfaces
Scoping with @AutoScoped
Generated code

Overview¶

For cases where you don't control instance creation (e.g., Retrofit interfaces), use the factory parameter with a ClassBindingFactory implementation. The processor generates @Provides functions that delegate to your factory.

Creating a Factory¶

Implement the ClassBindingFactory interface. The create method receives a KClass and returns an instance of that type:

class RetrofitBindingFactory @Inject constructor(
    private val retrofit: Retrofit,
) : ClassBindingFactory {

    @AutoScoped
    override fun <T : Any> create(kClass: KClass<T>): T {
        return retrofit.create(kClass.java)
    }
}

The factory class must have a primary constructor annotated with @Inject.

Annotating Interfaces¶

Point each interface to the factory using @AutoBinds(factory = ...):

@AutoBinds(factory = RetrofitBindingFactory::class)
interface UserApi {
    @GET("users/{id}")
    suspend fun fetchUser(@Path("id") id: Long): UserDto
}

@AutoBinds(factory = RetrofitBindingFactory::class)
interface PostApi {
    @GET("posts")
    suspend fun getPosts(): List<PostDto>
}

Each interface gets its own generated module, so you don't need to write @Provides functions manually.

Scoping with @AutoScoped¶

By default, generated @Provides functions are unscoped. Annotate the factory's create() method with @AutoScoped to add a scope annotation that matches the installIn component:

class RetrofitBindingFactory @Inject constructor(
    private val retrofit: Retrofit,
) : ClassBindingFactory {

    @AutoScoped  // adds @Singleton (or the scope matching installIn)
    override fun <T : Any> create(kClass: KClass<T>): T {
        return retrofit.create(kClass.java)
    }
}

The scope annotation is determined by the resolved component:

`installIn`	Scope added by `@AutoScoped`
`Singleton`	`@Singleton`
`ActivityRetained`	`@ActivityRetainedScoped`
`Activity`	`@ActivityScoped`
`ViewModel`	`@ViewModelScoped`
`Fragment`	`@FragmentScoped`
`View`	`@ViewScoped`
`ViewWithFragment`	`@ViewScoped`
`Service`	`@ServiceScoped`

Generated Code¶

For each annotated interface, the processor generates an object Hilt module:

@Module
@InstallIn(SingletonComponent::class)
internal object UserApiModule {
    @Provides
    @Singleton  // present only if @AutoScoped is used
    fun provideUserApi(factory: RetrofitBindingFactory): UserApi =
        factory.create(UserApi::class)
}