[MVP] - One Presenter for each View

General
1

Hi everybody,

i need some help with the mvp pattern which i´m using in my application for the first time.
is there one big presenter which “knows” all the views and the model
or
is there a presenter for each view?

Thanks for your help

2

Hi,

typically there’s a dedicated presenter for each view - otherwise you could quickly get a huge presenter which would not be maintainable or very clear.

-tepi

3

ok thank you.

then i was right and my coworker wrong :smiley:

4

another short question:

i´m using the viewprovider class from the dashboard example:

@SuppressWarnings("serial")
public class DashboardNavigator extends Navigator {

    private static final DashboardViews ERROR_VIEW = DashboardViews .SOURCE;
    private ViewProvider errorViewProvider;

    public DashboardNavigator (final ComponentContainer container) {
        super(UI.getCurrent(), container);

        initViewChangeListener();
        initViewProviders();

    }

    private void initViewChangeListener() {
        addViewChangeListener(new ViewChangeListener() {

            @Override
            public boolean beforeViewChange(final ViewChangeEvent event) {
                // Since there's no conditions in switching between the views
                // we can always return true.
                return true;
            }

            @Override
            public void afterViewChange(final ViewChangeEvent event) {
                DashboardViews view = DashboardViews.getByViewName(event.getViewName());
                // Appropriate events get fired after the view is changed.
                MyEventBus.post(new PostViewChangeEvent(view));
                MyEventBus.post(new BrowserResizeEvent());
                MyEventBus.post(new CloseOpenWindowsEvent());

            }
        });
    }

    private void initViewProviders() {
        // A dedicated view provider is added for each separate view type
        for (final DashboardViews viewType : DashboardViews.values()) {
            ViewProvider viewProvider = new ClassBasedViewProvider(viewType.getViewName(), viewType.getViewClass()) {

                // This field caches an already initialized view instance if the
                // view should be cached (stateful views).
                private View cachedInstance;

                @Override
                public View getView(final String viewName) {
                    View result = null;
                    if (viewType.getViewName().equals(viewName)) {
                        if (viewType.isStateful()) {
                            // Stateful views get lazily instantiated
                            if (cachedInstance == null) {
                                cachedInstance = super.getView(viewType
                                        .getViewName());
                            }
                            result = cachedInstance;
                        } else {
                            // Non-stateful views get instantiated every time
                            // they're navigated to
                            result = super.getView(viewType.getViewName());
                        }
                    }
                    return result;
                }
            };

            if (viewType == ERROR_VIEW) {
                errorViewProvider = viewProvider;
            }

            addProvider(viewProvider);
        }

        setErrorProvider(new ViewProvider() {
            @Override
            public String getViewName(final String viewAndParameters) {
                return ERROR_VIEW.getViewName();
            }

            @Override
            public View getView(final String viewName) {
                return errorViewProvider.getView(ERROR_VIEW.getViewName());
            }
        });
    }
}

the views are created in the “getView” method. but where should i add my presenter implementation?
Normaly i solve this problem like this: (https://vaadin.com/book/-/page/advanced.architecture.html)

// Create the model and the Vaadin view implementation
CalculatorModel    model = new CalculatorModel();
CalculatorViewImpl view  = new CalculatorViewImpl();
    
// The presenter binds the model and view together
new CalculatorPresenter(model, view);
    
// The view implementation is a Vaadin component
layout.addComponent(view);
5

anybody?!

6

Well, it can be done in a lot of various ways. The way I usually do it is that when you instantiate the view, it will create it’s own presenter and hook the view instance to it.

7

hmm ok thats one way to solve this problem but i want a way where the view doesnt know the presenter