CODEWITHSUNDEEP
javadagger-2provider
Elye
Elye

Reputation: 60261

How to provide Providers using Dagger 2 Multibinding as per the documentation

In reference to https://dagger.dev/multibindings.html, It is stated

If you want a map of providers, the Map.Entry objects in your multibound set should include the providers. Then your non-multibound map can have Provider values.

I try out the below code.

@Module
class MyModule {
  @Provides @IntoSet
  static Map.Entry<Foo, Provider<Bar>> entry(
      Provider<Bar> barProvider) {
    Foo key = ...;
    return new SimpleImmutableEntry(key, barProvider);
  }
}

@Module
class MyProviderMapModule {
  @Provides
  static Map<Foo, Provider<Bar>> fooBarProviderMap(
      Set<Map.Entry<Foo, Provider<Bar>>> entries) {
    return ...;
  }
}

It errors stating error: [Dagger/MissingBinding] Bar cannot be provided without an @Provides-annotated method. javax.inject.Provider<Bar> is injected at MyModule.entry(barProvider) java.util.Set<java.util.Map.Entry<Foo,Provider<Bar>>> is injected at MyModule.fooBarProviderMap(entries) java.util.Map<Foo,.Provider<Bar>> is provided at MyComponent.myMapFooProviderBar()

The reason is because it doesn't know how to generate Provider<Bar> barProvider. So I write the below

    @Provides
    static Provider<Bar> barProvider() {
        Provider<Bar> provider = new Provider<Bar>() {
            @Override
            public Bar get() {
                return Bar.create("1");
            }
        };
        return provider;
    }

It error out error: @Provides methods must not return framework types

How could I get the multibinding example works?

Upvotes: 1

Views: 1190

Answers (1)

Elye
Elye

Reputation: 60261

Apparently when we provide a Class Object, it could also provide the Provider.

@Provides
static Bar provideBar() {
    return Bar.create("xxx");
}

@Module
class MyModule {
  @Provides @IntoSet
  static Map.Entry<Foo, Provider<Bar>> entry(
      Provider<Bar> barProvider) {
    Foo key = ...;
    return new SimpleImmutableEntry(key, barProvider);
  }
}

@Module
class MyProviderMapModule {
  @Provides
  static Map<Foo, Provider<Bar>> fooBarProviderMap(
      Set<Map.Entry<Foo, Provider<Bar>>> entries) {
    return ...;
  }
}

Upvotes: 1

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