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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.

the data presentation widgets use a 'flyweight' design. Rather than being a container of other widgets, which can tend to be heavy, they build up chunks of HTML that is injected into the DOM. This not only speeds up initialization, but also reduces the event handling overhead that can slow down user experience when there are hundreds of widgets within a view.

The MVP Framework is an app framework that makes it easy for you to connect Data Presentation Widgets with backend data. Using this framework you create views that are focused on displaying data, Activities and an AcivityManager which are the "presenters", responsible for handling self-contained actions, and RequestFactories that fetch and propagate model changes throughout your app.

To make developing apps of this style easier, the 1.1 M1 release of Spring Roo, can generate and maintain the boilerplate code associated with connecting your app's components with GWT's MVP Framework.

MVP Framework The MVP Framework is an app framework that makes it easy for you to connect Data Presentation Widgets with backend data. Using this framework you create views that are focused on displaying data, Activities and an AcivityManager which are the "presenters", responsible for handling self-contained actions, and RequestFactories that fetch and propagate model changes throughout your app. To make developing apps of this style easier, the 1.1 M1 release of Spring Roo, can generate and maintain the boilerplate code associated with connecting your app's components with GWT's MVP Framework.

the data presentation widgets use a 'flyweight' design. Rather than being a container of other widgets, which can tend to be heavy, they build up chunks of HTML that is injected into the DOM. This not only speeds up initialization, but also reduces the event handling overhead that can slow down user experience when there are hundreds of widgets within a view.

To upgrade to 2.1 M1, simply do the following Download GWT 2.1 M1 from the download page and unpack it to the directory of your choice. If you use Eclipse to develop, you should also download the Google Plugin for Eclipse from the same download page. Update your GWT project build path to use the latest gwt-user.jar and gwt-dev.jar (and any other GWT jars that you included on your classpath). Replace references to gwt-dev-<platform>.jar with the location of the new gwt-dev.jar (there is no longer a platform specific suffix). Update any run configurations or application compile and shell scripts to include the latest JARs in the classpath (same JARs as mentioned in step 2). Run a GWT compilation over your project to generate the latest GWT application files for your project. Deploy the latest GWT application files to your web server.

I really do not approach the different features of 2.1 as a whole "MVP" set of things: there's  - RequestFactory and ValueStore (I don't think ValueStore has any real use besides RequestFactory, though I'd be happy to be proved wrong) for a record-oriented client-server communication;  - Cell-based widgets for efficient data-backed lists, trees and tables  - PlaceController as typed layer over History (objects rather than strings, even though it's not yet plumbed to History, which at least proves it can be used without it)  - ActivityManager as an "application controller" (to use the term from the GWT tutorials) on top of PlaceController  - and on top of that, GWT provides some base activities plumbed with RequestFactory  - and finally, though it's not documented at all, EditorSupport which works with UiBinder in a view to generate "data-binding code" (as far as I understood) You're free to use any of them independently of the others.

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

your ChatBoxPresenter isn't related to a "place", i.e. it's "awoken" based on a "business event", not a navigation event; and in other words, it's not an Activity: case made. Activities (ActivityManager) is limited in scope to reacting to place changes and navigation (not that you couldn't use the Activity "contract" in other scenarios, such as your "chat box", but the ActivityManager wouldn't be the right tool for the job, you'd have to find/write another "activity manager" for your different use case). In other words: GWT 2.1 Activities won't replace GWTP as a whole (and I believe, as I already said in the past, that it's not its goal either).

from what it seems to me the GWT 2.1 MVP is quite different than GWTP (and from GWT-MVP), and is not targeted to the same audience. I would say it is targeted to developers who want to develop Spring-GWT applications in a Grails/RoR way.

o summarize, here are some quotes: * It's extremely fast to build an initial scaffold (CRUD for all entities), but I'm not sure how easy it is to customize it for real world usage * When skimming the generated sources I saw A LOT of artifacts, which I don't feel comfortable with because it means that although "officially" my code is not coupled with Roo, if I were to drop it I would have to manage all these generated artifacts myself. * This expenses example is a nightmare to follow.  The bindings/ wiring  of all the pieces both client and server is nuts. * In M2, things have been cleaned up a bit

The MVP Framework is an app framework that makes it easy for you to connect Data Presentation Widgets with backend data. Using this framework you create views that are focused on displaying data, Activities and an ActivityManager which are the "presenters", responsible for handling self-contained actions, and RequestFactories that fetch and propagate model changes throughout your app. To make developing apps of this style easier, the 1.1 M1 release of Spring Roo, can generate and maintain the boilerplate code associated with connecting your app's components with GWT's MVP Framework.

It however clarify things about how Google sees MVP in GWT. They're even adding some MVP "framework" to GWT 2.1 (IsWidget and Activities, where an Activity is more or less your presenter, from what I understood).

RequestFactory on the other hand is a new thing for efficient CRUD operations on entity objects, which plugs more-or-less directly into the new Data widgets. Those widgets do blur the line a bit, but they're not really about presentation "logic", and they're somehow MVP- based themselves.

The main issue in MVC is that these three elements are tighly bound together: the controller has to register to both the model and the view (and unregister if either changes), and when a view serves multiple controllers or a controller uses multiple models, that becomes quickly a mess.

MVP approach is more message-oriented. All messages (events) are fired on a single EventBus that is shared by all Presenters. Each presenter listens to events of interest, and fires new events according to actions. So a change in the in the EmployeeModel may be fired with an EmployeeModelChangedEvent, instead of attaching a listener to the model object. And we can easily create new Presenters that receive that same event and react accordingly.

The magnitude of such a shift is great: the model is no more the center and source of events (which would require special care in attaching and detaching to a specific instance), but it more a passive container of data, which may be copied, proxied, transformed, cached, without the GWT appliction any special care.Since the model is more a container of data ment for communication, I've highlighted the fact that it needs to be Serializable.

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)