Is this an acceptable GWT solution

Question

I want to create a GWT UI where I basically will have a single HTML page that loads a PanelA object. The user will then do their thing and eventually perform an action that will move them onto another view/screen.
I have simplified my existing views to contain just a single button which moves the user onto the next page etc. for simplicity I only have 2 views to start. Here is my start up entry point.

public class StockWatcher implements EntryPoint 

{
    public void onModuleLoad()
    {
        final RootPanel rootPanel = RootPanel.get();
        rootPanel.add( PanelA.getInstance() );
    }
}

Here is the PanelA class

    public class PanelA extends HTMLPanel
    {
        private static PanelA panel;            
        private PanelA()
        {
            super("Panel A");
            final RootPanel rootPanel = RootPanel.get();

            Button btnNewButton = new Button("Go to panel B");
            btnNewButton.addClickHandler(new ClickHandler() {
                public void onClick(ClickEvent event) 
                {
                    rootPanel.clear();
                    rootPanel.add( PanelB.getInstance() );
                }
            });

            add(btnNewButton);
        }

        public static PanelA getInstance()
        {
            if (panel == null)
            {
                panel = new PanelA();
            }
            return panel;
        }
    }

My other PanelB class is pretty much the same as PanelA , ie button that brings me back to PanelA My UI works as desired. My Question is, Is this singleton type pattern a correct or proper way to do this? ie Have a stack of Singleton UI views that get popped on/off the main panel? Also, what is the best way to handle hitory/breadcrumb trace through a GWT app, ie allowing a user to go back to the previous screen bearing in mind that they may navigate to PanelX from either of PanelA, PanelB or PanelC

score 3 · Accepted Answer · answered Dec 26 '12 at 23:16

I use "Activities and Places" to manage all of this, and it's been working quite well in production for a year or so.

https://developers.google.com/web-toolkit/doc/latest/DevGuideMvpActivitiesAndPlaces

I think it's fine to use a Singleton mechanism for your views, but you have to make sure to completely reset any state you store. For me, it was easier to just create new views every time the user navigates to a new spot, and then if I detected a problem with load times or something to retroactively cause the view to re-use its components. I'd advise you to get the navigation working first, and then worry about the singleton (or not) optimizations.

score 1 · Answer 2 · answered Dec 26 '12 at 23:52

I recommend Activities and Places design pattern.

It covers all the issues you raise in your question, plus many more that you have not thought of (or did not ask about) yet, like native browser history management and ability to bookmark different places within the app, handling of page reloads, efficient memory management vs optimized DOM operations, scalability (building an app with dozens/hundreds of views with minimal code duplication), testability, and code-splitting (where to split large apps).

score 0 · Answer 3 · edited Jun 20 '20 at 09:12

I suggest you refer "GWTP" framework to make a GWT Project, some of the features currently supported by GWTP:

Dependency injection through GIN and Guice;
Simple but powerful history management mechanism;
Support for nested presenters;
Lazy instantiation for presenter and view;
Effortless and efficient code splitting;
Integrated command pattern supporting undo/redo;

So your questions and query like Singleton UI views, best way to handle hitory/breadcrumb trace and singleton type pattern , will cover and one good framework will make easy project management.

Is this an acceptable GWT solution

3 Answers3