使用 Hilt/Dagger2 注入密封类

Question

I have to inject a sealed class through constructor, but I am receiving the compiling error:

• Cannot be provided without an @Provides-annotated method

So, what I'm trying to do is to create a sealed like this:

sealed class Alphabet {
    object A: Alphabet()
    object B: Alphabet()
    data class C (val x: String): Alphabet()
    data class D (val y: Int): Alphabet()
}

And inject it in the constructor of another class like this:

@ViewModelScoped
class RandomUseCase @Inject constructor(
    private val alphabet: Alphabet
) {
    val z = when (alphabet) {
        A -> ...
        B -> ...
        C -> alphabet.x
        D -> alphabet.y
    }

So, how can I inject this?

Answer 1

So, according to Kotlin official documentation Constructor of Sealed classes are private by default and Hilt needs a visible constructor to get its implementation from.

Link for reference here:

And by reading you question i am really not sure why do you need a sealed class here. The purpose of injecting a class or a implementation is to get a per-instantiated object but in case of sealed class you can't directly instantiate sealed class in its Hilt module like below.

@Singleton
@Binds
abstract fun provideAlphabet(alphabet: Alphabet): Alphabet

Suggestions:

Instead of injecting sealed class and using it in a function, you can simply pass a sealed class object in function and then compare it in function like this.

 fun sampleForSealed() {
    
    sampleForPassingSealed(Alphabet.A)
}

fun sampleForPassingSealed(alphabet: Alphabet) {
    when (alphabet) {
        Alphabet.A -> {

        }
        Alphabet.B -> {

        }
    }
}

Happy Coding!