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android – Dagger 2 multibindings with Kotlin

Posted by: admin April 23, 2020 Leave a comment

Questions:

I have the following snippet in my dagger 2 module

@Singleton
@Provides
@ElementsIntoSet
fun providesQueries(foo: Foo): Set<Foo>{
    val queries = LinkedHashSet<Foo>()
    queries.add(foo)
    return queries
}

I try to inject into in this way

@Inject lateinit var foo: Set<Foo>

But dagger shows an error which says that Dagger cannot provides java.util.Set without @Provides or @Produces method.

I did the same in java and it worked. Does somebody know why is it failing?

How to&Answers:

As it described in the Kotlin reference

To make Kotlin APIs work in Java we generate Box<Super> as
Box<? extends Super> for covariantly defined Box (or Foo<? super Bar> for
contravariantly defined Foo) when it appears as a parameter.

You can use @JvmSuppressWildcards for avoiding it, just as following:

@Inject lateinit var foo: Set<@JvmSuppressWildcards Foo>