Dagger 2.11 ContributesAndroidInjector Singleton dependency injection fails

Question

I am exploring the new dagger.android from Dagger 2.11. I hope not to have to create custom scope annotation like @PerActivity. So far I was able to do the following:

1) Define Application scope Singletons and injecting them into activities.

2) Define Activity scope non-Singleton dependencies and injecting them into their activities using @ContributesAndroidInjector

What I cannot figure out is how to have an Application scope Singleton and Activity scope non-Singletons using it.

In the example below, I would like my Activity scope MyActivityDependencyA and MyActivityDependencyB to have access to a Singleton MyActivityService

The setup below results in:

Error:(24, 3) error: com.example.di.BuildersModule_BindMyActivity.MyActivitySubcomponent (unscoped) may not reference scoped bindings: @Singleton @Provides com.example.MyActivityService com.example.MyActivitySingletonsModule.provideMyActivityService()

Here is my setup. Note, I defined separate MyActivitySingletonsModule and MyActivityModule since I could not mix Singleton and non-Singleton dependencies in the same Module file.

@Module
public abstract class BuildersModule {
    @ContributesAndroidInjector(modules = {MyActivitySingletonsModule.class, MyActivityModule.class})
    abstract MyActivity bindMyActivity();
    }
}

and

@Module
public abstract class MyActivityModule {
    @Provides
    MyActivityDependencyA provideMyActivityDependencyA(MyActivityService myActivityService){
       return new MyActivityDependencyA(myActivityService);
    }
    @Provides
    MyActivityDependencyB provideMyActivityDependencyB(MyActivityService myActivityService) {
        return new MyActivityDependencyB(myActivityService);
    }
}

and

@Module
public abstract class MyActivitySingletonsModule {
    @Singleton
    @Provides
    MyActivityService provideMyActivityService() {
        return new MyActivityService();
    }
}

and

@Singleton
 @Component(modules = {
    AndroidSupportInjectionModule.class,
    AppModule.class,
    BuildersModule.class})

public interface AppComponent {
    @Component.Builder
    interface Builder {
        @BindsInstance
        Builder application(App application);
        AppComponent build();
    }
    void inject(App app);
}

Is it even possible to do what I am trying to do without defining custom scope annotations?

Thanks in advance!

Answer 1

Why avoid custom scopes? Custom scopes are still required for the new dagger.android dependency injection framework introduced in Dagger 2.10+.

"My understanding is @ContributesAndroidInjector removes the need for custom annotation and I was able to prove it by using non-singletons defined in the activity scope without any issues."

@ContributesAndroidInjector (available in v2.11) does not remove the need for custom scopes. It merely replaces the need to declare @Subcomponent classes that does not make use of @Subcomponent.Builder to inject dependencies required by the component at runtime. Take a look at the below snippet from the official dagger.android user guide about @ContributesAndroidInjector;

"Pro-tip: If your subcomponent and its builder have no other methods or supertypes than the ones mentioned in step #2, you can use @ContributesAndroidInjector to generate them for you. Instead of steps 2 and 3, add an abstract module method that returns your activity, annotate it with @ContributesAndroidInjector, and specify the modules you want to install into the subcomponent. If the subcomponent needs scopes, apply the scope annotations to the method as well."

@ActivityScope
@ContributesAndroidInjector(modules = { /* modules to install into the subcomponent */ })
abstract YourActivity contributeYourActivityInjector();

The key here is "If the subcomponent needs scopes, apply the scope annotations to the method as well."

Take a look at the following code for an overview of how to use @Singleton, @PerActivity, @PerFragment, and @PerChildFragment custom scopes with the new dagger.android injection framework.

// Could also extend DaggerApplication instead of implementing HasActivityInjector
// App.java
public class App extends Application implements HasActivityInjector {

    @Inject
    AppDependency appDependency;

    @Inject
    DispatchingAndroidInjector<Activity> activityInjector;

    @Override
    public void onCreate() {
        super.onCreate();
        DaggerAppComponent.create().inject(this);
    }

    @Override
    public AndroidInjector<Activity> activityInjector() {
        return activityInjector;
    }
}

// AppModule.java
@Module(includes = AndroidInjectionModule.class)
abstract class AppModule {
    @PerActivity
    @ContributesAndroidInjector(modules = MainActivityModule.class)
    abstract MainActivity mainActivityInjector();
}

// AppComponent.java
@Singleton
@Component(modules = AppModule.class)
interface AppComponent {
    void inject(App app);
}

// Could also extend DaggerActivity instead of implementing HasFragmentInjector
// MainActivity.java
public final class MainActivity extends Activity implements HasFragmentInjector {

    @Inject
    AppDependency appDependency; // same object from App

    @Inject
    ActivityDependency activityDependency;

    @Inject
    DispatchingAndroidInjector<Fragment> fragmentInjector;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        AndroidInjection.inject(this);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        if (savedInstanceState == null) {
            addFragment(R.id.fragment_container, new MainFragment());
        }
    }

    @Override
    public final AndroidInjector<Fragment> fragmentInjector() {
        return fragmentInjector;
    }
}

// MainActivityModule.java
@Module
public abstract class MainActivityModule {
    @PerFragment
    @ContributesAndroidInjector(modules = MainFragmentModule.class)
    abstract MainFragment mainFragmentInjector();
}

// Could also extend DaggerFragment instead of implementing HasFragmentInjector
// MainFragment.java
public final class MainFragment extends Fragment implements HasFragmentInjector {

    @Inject
    AppDependency appDependency; // same object from App

    @Inject
    ActivityDependency activityDependency; // same object from MainActivity

    @Inject
    FragmentDependency fragmentDepency; 

    @Inject
    DispatchingAndroidInjector<Fragment> childFragmentInjector;

    @SuppressWarnings("deprecation")
    @Override
    public void onAttach(Activity activity) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
            // Perform injection here before M, L (API 22) and below because onAttach(Context)
            // is not yet available at L.
            AndroidInjection.inject(this);
        }
        super.onAttach(activity);
    }

    @Override
    public void onAttach(Context context) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // Perform injection here for M (API 23) due to deprecation of onAttach(Activity).
            AndroidInjection.inject(this);
        }
        super.onAttach(context);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.main_fragment, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        if (savedInstanceState == null) {
            addChildFragment(R.id.child_fragment_container, new MainChildFragment());
        }
    }

    @Override
    public final AndroidInjector<Fragment> fragmentInjector() {
        return childFragmentInjector;
    }
}

// MainFragmentModule.java
@Module
public abstract class MainFragmentModule {
    @PerChildFragment
    @ContributesAndroidInjector(modules = MainChildFragmentModule.class)
    abstract MainChildFragment mainChildFragmentInjector();
}

// MainChildFragment.java
public final class MainChildFragment extends Fragment {

    @Inject
    AppDependency appDependency; // same object from App

    @Inject
    ActivityDependency activityDependency; // same object from MainActivity

    @Inject
    FragmentDependency fragmentDepency; // same object from MainFragment

    @Inject
    ChildFragmentDependency childFragmentDepency;

    @Override
    public void onAttach(Context context) {
        AndroidInjection.inject(this);
        super.onAttach(context);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.main_child_fragment, container, false);
    }
}

// MainChildFragmentModule.java
@Module
public abstract class MainChildFragmentModule {
}

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

// PerFragment.java
@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface PerFragment {
}

// PerChildFragment.java
@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface PerChildFragment {
}

// AppDependency.java
@Singleton
public final class AppDependency {
    @Inject
    AppDependency() {
    }
}

// ActivityDependency.java
@PerActivity
public final class ActivityDependency {
    @Inject
    ActivityDependency() {
    }
}

// FragmentDependency.java
@PerFragment
public final class FragmentDependency {
    @Inject
    FragmentDependency() {
    }
} 

// ChildFragmentDependency.java
@PerChildFragment
public final class ChildFragmentDependency {
    @Inject
    ChildFragmentDependency() {
    }
}

For a complete dagger.android 2.11 setup guide using @ContributesAndroidInjector and custom scopes mentioned above, read this article.