A: Dagger.android 2.11 simple example with support for Singleton, PerActivity, PerFragment, and PerChildFragment scopes

Dagger2SimpleExample.java

// This is a super simplified example of how to use the new dagger.android framework
// Forked from https://gist.github.com/vestrel00/64be913f954989fe52c674247e093218/
// but changed to have less boilerplate using the new features.
// Used on https://github.com/ebraminio/DroidPersianCalendar also

// App.java
public class App extends DaggerApplication {
    @Override
    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
        return DaggerAppComponent.builder().create(this);
    }
}

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

// AppComponent.java
@Singleton
@Component(modules = {AndroidSupportInjectionModule.class, AppModule.class})
public interface AppComponent extends AndroidInjector<App> {
    @Component.Builder
    abstract class Builder extends AndroidInjector.Builder<App> {
    }
}

// MainActivity.java
public final class MainActivity extends DaggerActivity {

    @Inject
    AppDependency appDependency; // same object from App
  
    @Inject
    ActivityDependency activityDependency;
  
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        if (savedInstanceState == null) {
            addFragment(R.id.fragment_container, new MainFragment());
        }
    }
  
    private final void addFragment(@IdRes int containerViewId, Fragment fragment) {
        getFragmentManager.beginTransaction()
                .add(containerViewId, fragment)
                .commit();
    }
}

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

// MainFragment.java
// Could instead extend DialogFragment to add DialogFragment capabilities.
// DialogFragments may be embedded as regular fragments in a view of an Activity or Fragment
// and may also be shown as a dialog or in an alert dialog.
public final class MainFragment extends DaggerFragment {

    @Inject
    AppDependency appDependency; // same object from App
  
    @Inject
    ActivityDependency activityDependency; // same object from MainActivity
  
    @Inject
    FragmentDependency fragmentDependency; 
  
    @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());
        }
    }
  
    private final void addChildFragment(@IdRes int viewId, Fragment fragment) {
        getChildFragmentManager()
                .beginTransaction()
                .add(viewId, fragment)
                .commit();
    }
}

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

// MainChildFragment.java
public final class MainChildFragment extends DaggerFragment {
  
    @Inject
    AppDependency appDependency; // same object from App
  
    @Inject
    ActivityDependency activityDependency; // same object from MainActivity
  
    @Inject
    FragmentDependency fragmentDependency; // same object from MainFragment
  
    @Inject
    ChildFragmentDependency childFragmentDependency;
  
    @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() {
    }
}