I haven't looked into using child scopes since I created this repository and my projects are still using Dagger 1. Things like Subcomponents and other aspects exist now that didn't exist when I had originally looked into the original scoping issue, so I'm sure this is out of date and there may be a better way of approaching this now if you need this sort of thing.

Dagger is a super useful tool for dependency injection in Android. A neat feature of Dagger was the ability to "plus" your object graph to create a new scoped object graph.

Dagger 2 uses components to provide scoping. However, Dagger 2's components have pretty strict rules on what you can and cannot do.

In trying out Dagger 2, I was a little confused as to the proper way of building these scoped components that referenced bindings provided in parent scopes. This repo shows a simple, albeit contrived, way of referencing bindings in a parent scope.

Any dependency you want to provide to the child scopes, you need to expose them via the parent component's interface. Here, I expose the OkHttpClient dependency provided by the NetworkModule.

@Singleton
@Component(modules = {AppModule.class, NetworkModule.class})
  public interface AppComponent {
    ComponentTest app();
    OkHttpClient httpClient();

    void inject(ComponentTest app);
  }
}

In the child component/scope, you depend on the parent component and extend it, which gives your child component visibility to the dependencies exposed via the parent interface. See the discussion in this GitHub issue for more details.

@ActivityScope
@Component(dependencies = AppComponent.class, modules = ActivityModule.class)
public interface ActivityComponent extends AppComponent {
    void inject(MainActivity activity);
}