A: 3 - ui/common/BaseActivity.java

BaseActivity.java

public abstract class BaseActivity extends Activity implements HasFragmentInjector {

    @Inject
    @Named(BaseActivityModule.ACTIVITY_FRAGMENT_MANAGER)
    protected FragmentManager fragmentManager;

    @Inject
    DispatchingAndroidInjector<Fragment> fragmentInjector;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        AndroidInjection.inject(this);
        super.onCreate(savedInstanceState);
    }

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

    protected final void addFragment(@IdRes int containerViewId, Fragment fragment) {
        fragmentManager.beginTransaction()
                .add(containerViewId, fragment)
                .commit();
    }
}