Model-view-presenter pattern

Magnolia uses the model-view-presenter pattern. The separation of views and presenters is done consistently throughout the application on server and client and within complex components. The presenter reacts on events raised by user interaction, driving the view by populating it with data to display.

UI events

Magnolia uses a model view presenter pattern to handle UI events.

• The View does not implement business logic or communicate with the Model. The view provides the interface to the end user and reacts on and informs the Presenter about user actions (input). 
• The View and Presenter communicate together.
• The Presenter uses the Model to fetch data and implements business logic, informing the View to display content (such as a form).

• The View interface defines a Listener interface that is implemented by the Presenter. The purpose of the Listener interface is to ensure that the view does not inadvertently communicate to the Presenter.
• The Listener methods are implemented by the Presenter; the callback methods from the view to the Presenter.

• The Presenter only knows about the View's Interface;  this ensures that the Presenter is not bypassing the pattern and cannot directly communicate to the View implementation.

MVP and the app framework

Here we look at an example of how the MVP pattern is employed in a subapp.

1. The View's interface defines an inline Listener interface with the method greetUser(String user).

public interface HelloWorldMainSubAppView extends View {
    void setListener(Listener listener);
    void addUser(String user);
    
    public interface Listener {
        void greetUser(String user);
    }
}

2. The Presenter (subclass) implements: 

• • View inline listener interface and  the greetUser(String user) callback method. The method is called by the View (via the listener) on user input through the UI.
  • The interface type of the View is determined by the getView() method.
  • The Presenter registers itself as the View's Listener using the onSubAppStart() method.
  • In the onSubAppStart()method the Presenter calls the View's interface getView().addUser("Lisa")method.

//The Presenter implements the View's Listener by providing the View's callback method to the Presenter.
public class HelloWorldMainSubApp extends BaseSubApp implements HelloWorldMainSubAppView.Listener {
    private LocationController locationController;

	// The View is injected into the Presenter's constructor. The View's implementation is defined by the IOC component provider.
    @Inject
    public HelloWorldMainSubApp(final SubAppContext subAppContext, HelloWorldMainSubAppView view, LocationController locationController) {
        super(subAppContext, view);
        // Set the location controller
        this.locationController = locationController;
    }

	// Defines the implementation of the injected view in use.
    @Override
    public HelloWorldMainSubAppView getView() {
        return (HelloWorldMainSubAppView) super.getView();
    }

	@Override
    protected void onSubAppStart() {
        // Register this presenter as the View's Listener.
        getView().setListener(this);
        // Call the view to display something.
        getView().addUser("Lisa");
    }

	// Implements the View's Listener method. Is the View's callback function to the presenter.
    @Override
    public void greetUser(String user) {
        // Do what ever logic needed triggered by this UI action.
    }
}

View calls  the Presenter via the Listener's callback-function listener.greetUser(user):

@Override
public void addUser(final String user) {
    Button button = new Button("Say hello to " + user + "!");
    button.addClickListener(new Button.ClickListener() {
        @Override
        public void buttonClick(Button.ClickEvent event) {
            listener.greetUser(user);
        }
    });
    layout.addComponent(button);
 }