IToolbarEventListener.java

public interface IToolbarEventListener {

    void onNewTitle(String title);

    void onNewSubtitle(String subtitle);
}

IToolbarModelMutator.java

public interface IToolbarModelMutator {

    void setTitle(String title);

    void setSubtitle(String subtitle);
}

IToolbarModelObserver.java

public interface IToolbarModelObserver {

    String getTitle();

    String getSubtitle();

    void setListener(IToolbarEventListener listener);
}

IViewModelComponent.java

public interface IViewModelComponent {

    @NonNull
    ToolbarModule toolbarViewModels();

    @NonNull
    LabelsModule labelsModule();
}

MainActivity.java

public class MainActivity {
  
  ...
    
  //Здесь мы просто создаем фабрику для презентера, важно для понимания только то, что мы инжектим туда обзервер модели
  @NonNull
    @Override
    protected ViperPresenter.Factory<IMainView, MainRouter, MainPresenter> provideFactory() {
        return new MainPresenter.Factory(provideToolbarModelObserver());
    }
  
  @NonNull
    @Override
    public IToolbarModelMutator provideToolbarModelMutator() {
        verifyComponentProvidersExist();
        return ((RetainContainer<IViewModelComponent>) getSupportFragmentManager()
                .findFragmentByTag(TAG_VIEW_MODEL_CONTAINER))
                .provideComponent()
                .toolbarViewModels()
                .provideToolbarModelMutator();
    }

    @NonNull
    @Override
    public IToolbarModelObserver provideToolbarModelObserver() {
        verifyComponentProvidersExist();
        return ((RetainContainer<IViewModelComponent>) getSupportFragmentManager()
                .findFragmentByTag(TAG_VIEW_MODEL_CONTAINER))
                .provideComponent()
                .toolbarViewModels()
                .provideToolbarModelObserver();
    }
  
  private void verifyComponentProvidersExist() {
        if(getSupportFragmentManager().findFragmentByTag(TAG_VIEW_MODEL_CONTAINER) == null) {
            RetainContainer<IViewModelComponent> container = new RetainContainer<>();
            IApplicationEnvironmentProvider applicationEnvironmentProvider = (IApplicationEnvironmentProvider) getApplication();
            container.setFactory(new ViewModelComponentFactory(applicationEnvironmentProvider.provideContext()));
            getSupportFragmentManager().beginTransaction()
                    .add(container, TAG_VIEW_MODEL_CONTAINER)
                    .commitNow();
        }
    } 
  
  ...
    
}

MainPresenter.java

public class MainPresenter extends ViperPresenter<IMainView, MainRouter> implements IToolbarEventListener {

    @NonNull
    private final IToolbarModelObserver toolbarModelObserver;

    public MainPresenter(@NonNull IToolbarModelObserver toolbarModelObserver) {
        this.toolbarModelObserver = toolbarModelObserver;
    }

    @Override
    protected void onViewAttach() {
        getView().setTitle(toolbarModelObserver.getTitle());
        getView().setSubtitle(toolbarModelObserver.getSubtitle());
        toolbarModelObserver.setListener(this);
    }

    @Override
    protected void onViewDetach() {
        toolbarModelObserver.setListener(null);
    }

    @Override
    protected void onDestroy() {

    }

    @Override
    public void onNewTitle(String title) {
        getView().setTitle(title);
    }

    @Override
    public void onNewSubtitle(String subtitle) {
        getView().setSubtitle(subtitle);
    }

    ...

    public static final class Factory implements ViperPresenter.Factory<IMainView, MainRouter, MainPresenter> {

        @NonNull
        private final IToolbarModelObserver toolbarModelObserver;

        public Factory(@NonNull IToolbarModelObserver toolbarModelObserver) {
            this.toolbarModelObserver = toolbarModelObserver;
        }

        @Override
        public MainPresenter create() {
            return new MainPresenter(toolbarModelObserver);
        }
    }
}

PreferencesFragment.java

public class PreferencesFragment {
  
  //Здесь важно, что мы инжектим мутатор в презентер
  @NonNull
    @Override
    protected ViperPresenter.Factory<IPreferencesView, MainRouter, PreferencesPresenter> provideFactory() {
        ILabelsManagerProvider labelsManagerProvider = (ILabelsManagerProvider) getActivity();
        IToolbarViewModelProvider toolbarViewModelProvider = (IToolbarViewModelProvider) getActivity();

        return new PreferencesPresenter.Factory(
                labelsManagerProvider.provideLabelsManager(),
                toolbarViewModelProvider.provideToolbarModelMutator()
        );
    }
}

PreferencesPresenter.java

public class PreferencesPresenter extends ViperPresenter<IPreferencesView, MainRouter> {

    @NonNull
    private final ILabelsManager labelsManager;

    @NonNull
    private final IToolbarModelMutator toolbarModelMutator;

    private PreferencesPresenter(@NonNull ILabelsManager labelsManager,
                                 @NonNull IToolbarModelMutator toolbarModelMutator) {

        this.labelsManager = labelsManager;
        this.toolbarModelMutator = toolbarModelMutator;
    }

    @Override
    protected void onViewAttach() {
        toolbarModelMutator.setTitle(labelsManager.getPreferencesLabel());
        toolbarModelMutator.setSubtitle("");
        getView().setVersionCode(BuildConfig.VERSION_CODE);
        getView().setVersionName(BuildConfig.VERSION_NAME);
    }

    @Override
    protected void onViewDetach() {

    }

    @Override
    protected void onDestroy() {

    }
    
    public static final class Factory implements ViperPresenter.Factory<IPreferencesView, MainRouter, PreferencesPresenter> {

        @NonNull
        private final ILabelsManager labelsManager;

        @NonNull
        private final IToolbarModelMutator toolbarModelMutator;

        public Factory(@NonNull ILabelsManager labelsManager,
                       @NonNull IToolbarModelMutator toolbarModelMutator) {
            this.labelsManager = labelsManager;
            this.toolbarModelMutator = toolbarModelMutator;
        }

        @Override
        public PreferencesPresenter create() {
            return new PreferencesPresenter(labelsManager, toolbarModelMutator);
        }
    }
}

RetainContainer.java

public class RetainContainer<Component> extends Fragment {

    @NonNull
    private final Object lock = new Object();

    @Nullable
    private volatile Component component;

    private Factory<Component> factory;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    @NonNull
    public Component provideComponent() {
        Component localInstance = component;
        if(localInstance == null) {
            synchronized (lock) {
                localInstance = component;
                if(localInstance == null) {
                    localInstance = component = factory.create();
                }
            }
        }

        return localInstance;
    }

    public void setFactory(Factory<Component> factory) {
        this.factory = factory;
    }

    public interface Factory<T> {

        T create();
    }
}

ToolbarModel.java

public class ToolbarModel implements IToolbarModelObserver, IToolbarModelMutator {

    private String title;

    private String subtitle;

    private IToolbarEventListener listener;

    public ToolbarModel() {

    }

    @Override
    public void setTitle(String title) {
        this.title = title;
        listener.onNewTitle(this.title);
    }

    @Override
    public void setSubtitle(String subtitle) {
        this.subtitle = subtitle;
        listener.onNewSubtitle(this.subtitle);
    }

    @Override
    public String getTitle() {
        return this.title;
    }

    @Override
    public String getSubtitle() {
        return this.subtitle;
    }

    @Override
    public void setListener(IToolbarEventListener listener) {
        this.listener = listener;
    }
}

ToolbarModule.java

public class ToolbarModule {

    @NonNull
    private final Object lock = new Object();

    @Nullable
    private volatile ToolbarModel model;

    public ToolbarModule() {

    }

    @NonNull
    public IToolbarModelMutator provideToolbarModelMutator() {
        IToolbarModelMutator localInstance = model;
        if(localInstance == null) {
            synchronized (lock) {
                localInstance = model;
                if(localInstance == null) {
                    localInstance = model = new ToolbarModel();
                }
            }
        }

        return localInstance;
    }

    @NonNull
    public IToolbarModelObserver provideToolbarModelObserver() {
        IToolbarModelObserver localInstance = model;
        if(localInstance == null) {
            synchronized (lock) {
                localInstance = model;
                if(localInstance == null) {
                    localInstance = model = new ToolbarModel();
                }
            }
        }

        return localInstance;
    }
}

ViewModelComponent.java

public class ViewModelComponent implements IViewModelComponent {

    @NonNull
    private final ToolbarModule toolbar;

    @NonNull
    private final LabelsModule labelsModule;

    public ViewModelComponent(Context context) {
        this.toolbar = new ToolbarModule();
        this.labelsModule = new LabelsModule(context.getResources());
    }

    @NonNull
    @Override
    public ToolbarModule toolbarViewModels() {
        return toolbar;
    }

    @NonNull
    @Override
    public LabelsModule labelsModule() {
        return labelsModule;
    }
}

ViewModelComponentFactory.java

public class ViewModelComponentFactory implements RetainContainer.Factory<IViewModelComponent> {

    @NonNull
    private final Context context;

    public ViewModelComponentFactory(@NonNull Context context) {
        this.context = context;
    }

    @Override
    public IViewModelComponent create() {
        return new ViewModelComponent(context);
    }
}