Dagger 2: Provide same instance between multiple Component with same Scope on different library modules

Question

I have a Core Android Library where I\'m defining a CoreComponent ad using the @Singleton scope to inject instances of classes provided by a CoreModule.

@Sin         


        

Answer 1

Remove the injection sites from your CoreComponent - it now has the sole function of exposing the binding for CoreRepository to its dependent components:

@Singleton
@Component(modules = {CoreModule.class})
public interface CoreComponent {
    CoreRepository coreRepository();
}

Create a reference to this singleton-scoped component inside your application:

public class MyApplication extends Application {
    private final CoreComponent coreComponent;

    @Override
    public void onCreate() {
        super.onCreate();
        coreComponent = DaggerCoreComponent
                            .coreModule(new CoreModule())
                            .build();
    }

    public static CoreComponent getCoreComponent(Context context) {
        return ((MyApplication) context.getApplicationContext()).coreComponent;
    }
}

Create a new narrower scope:

@Scope
@Retention(RetentionPolicy.RUNTIME) public @interface PerActivity {}

Create a new component that tracks this scope complete with the injection sites you want:

@PerActivity
@Component(dependencies = {CoreComponent.class})
public interface ActivityComponent {
    void inject(FooActivity activity);

    void inject(BarActivity activity);
}

When you access this activity-scoped component in the injection site, you will need to provide the instance of CoreComponent to the builder. Now you can inject into your Activity

public class FooActivity extends AppCompatActivity {
        @Inject
        public CoreRepository repo;

        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            CoreComponent coreComponent = MyApplication.getCoreComponent(this);
            DaggerActivityComponent.builder()
                .coreComponent(coreComponent)
                .build()
                .inject(this);
        }
    }
}