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he generally adopted way of doing things in GWT is to have custom events go through the event bus. In this case, you're talking about "navigation", so maybe the concept of "place" would be better than "just" some custom event. I encourage you to look at gwt-platform, gwt- presenter and other MVP frameworks for GWT, and/or look at the Activity concept from the upcoming GWT 2.1. Using actvities, you'd have an ActivityManager managing your "center". The tree would use the PlaceController.goTo to navigate to a new "place". An ActivityMapper (that you passed to the ActivityManager in the constructor) would map the place to an Activity (a presenter), and the ActivityManager will manage the current Activity for the display it manages, i.e.it will stop() the current activity if its ok (willStop returns true) and then only start the new Activity, which will call the Display back to show its view. The tree would probably also listen to PlaceChangeEvent on the event bus to update the selected item depending on the current place (in case some other component calls the PlaceController.goTo)

he generally adopted way of doing things in GWT is to have custom events go through the event bus. In this case, you're talking about "navigation", so maybe the concept of "place" would be better than "just" some custom event. I encourage you to look at gwt-platform, gwt- presenter and other MVP frameworks for GWT, and/or look at the Activity concept from the upcoming GWT 2.1.

Using actvities, you'd have an ActivityManager managing your "center". The tree would use the PlaceController.goTo to navigate to a new "place". An ActivityMapper (that you passed to the ActivityManager in the constructor) would map the place to an Activity (a presenter), and the ActivityManager will manage the current Activity for the display it manages, i.e.it will stop() the current activity if its ok (willStop returns true) and then only start the new Activity, which will call the Display back to show its view. The tree would probably also listen to PlaceChangeEvent on the event bus to update the selected item depending on the current place (in case some other component calls the PlaceController.goTo)

Views A key concept of MVP development is that a view is defined by an interface. This allows multiple view implementations based on client characteristics (such as mobile vs. desktop) and also facilitates lightweight unit testing by avoiding the time-consuming GWTTestCase. There is no View interface or class in GWT which views must implement or extend; however, GWT 2.1 introduces an IsWidget interface that is implemented by most Widgets as well as Composite. It is useful for views to extend IsWidget if they do in fact provide a Widget. Here is a simple view from our sample app. public interface GoodbyeView extends IsWidget {    void setName(String goodbyeName);} The corresponding implementation extends Composite, which keeps dependencies on a particular Widget from leaking out. public class GoodbyeViewImpl extends Composite implements GoodbyeView {    SimplePanel viewPanel = new SimplePanel();    Element nameSpan = DOM.createSpan();    public GoodbyeViewImpl() {        viewPanel.getElement().appendChild(nameSpan);        initWidget(viewPanel);    }    @Override    public void setName(String name) {        nameSpan.setInnerText("Good-bye, " + name);    }}

A place in GWT 2.1 is a Java object representing a particular state of the UI. A Place can be converted to and from a URL history token (see GWT's History object) by defining a PlaceTokenizer for each Place, and the PlaceHistoryHandler automatically updates the browser URL corresponding to each Place in your app.

Place

Activities are more tied to the concept of Places than of MVP, i.e. navigation and user experience rather than code structure ("developer experience").

An activity in GWT 2.1 is analogous to a presenter in MVP terminology. It contains no Widgets or UI code. Activities are started and stopped by an ActivityManager associated with a container Widget. A powerful new feature in GWT 2.1 is that an Activity can automatically display a warning confirmation when the Activity is about to be stopped (such as when the user navigates to a new Place). In addition, the ActivityManager warns the user before the window is about to be closed.

A place in GWT 2.1 is a Java object representing a particular state of the UI. A Place can be converted to and from a URL history token (see GWT's History object) by defining a PlaceTokenizer for each Place, and the PlaceHistoryHandler automatically updates the browser URL corresponding to each Place in your app.

A key concept of MVP development is that a view is defined by an interface.

Ray Ryan - These posts are right on the money, Thomas. I think you hit the problem with this approach too: you still need nested Place objects, and those are a nuisance to make. E.g., in a master detail you might need to record both the page of the master list that is showing as well as which detail set. Maybe the thing to do is add a CompositePlace to GWT?Sep 14

Ray Ryan - The idea is that parents are an optical illusion. There is an activity that knows how to show lists of things. There is another that knows how to show details. In one arrangement of your app they may be on the screen at the same time. In another (*cough* mobile *cough*), they aren't. They really shouldn't know about each other.Sep 14

the key concept here is that an Activity can be a Presenter but a Presenter is not necessarily an activity.Oct 26DeleteUndo deleteReport spamNot spamRay Ryan - Exactly: not every presenter needs to bother being an activity.Oct