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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.

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

Entity proxies simply extend the EntityProxy interface and use the @ProxyFor annotation to reference the server-side entity being represented. It is not necessary to represent every property and method from the server-side entity in the EntityProxy, only getters and setters for properties that should be exposed to the client. Note that while getId() is shown in this example, most client code will want to refer to EntityProxy.stableId() instead, as the EntityProxyId returned by this method is used throughout RequestFactory-related classes. Also note that the getSupervisor() method returns another proxy class (EmployeeProxy). All client-side code must reference EntityProxy subclasses. RequestFactory automatically converts proxy types to their corresponding entity types on the server.

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.

How to navigate To navigate to a new Place in your application, call the goTo() method on your PlaceController. This is illustrated above in the goTo() method of HelloActivity. PlaceController warns the current Activity that it may be stopping (via a PlaceChangeRequest event) and once allowed, fires a PlaceChangeEvent with the new Place. The PlaceHistoryHandler listens for PlaceChangeEvents and updates the URL history token accordingly. The ActivityManager also listens for PlaceChangeEvents and uses your app's ActivityMapper to start the Activity associated with the new Place. Rather than using PlaceController.goTo(), you can also create a Hyperlink containing the history token for the new Place obtained by calling your PlaceHistoryMapper.getToken(). When the user navigates to a new URL (via hyperlink, back button, or bookmark), PlaceHistoryHandler catches the ValueChangeEvent from the History object and calls your app's PlaceHistoryMapper to turn the history token into its corresponding Place. It then calls PlaceController.goTo() with the new Place. What about apps with multiple panels in the same window whose state should all be saved together in a single URL? GWT 2.1 does not attempt to provide a generic implementation of a composite Place; however, your app could create a CompositePlace, CompositeActivity, and CompositePlace.Tokenizer classes that delegate to the constituent members. In this case, only the composite objects would need to be registered with your app's ActivityMapper and PlaceHistoryMapper.

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.