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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 way we're minimizing code right now, is by creating some useful abstract tokenizers that handle the common use cases (no parameter tokenizer, key-value pair tokenizer). With those there are corresponding abstract tokenizers that handle creating the hashCode and equals methods. Aside from the 1:1 between Place and Activity, which bothers me in principle but may not be a practical concern just yet, it's coming along pretty nicely.

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.

often your places are "parameterized", think of a detail/edit screen for example that needs the model's id. The token is a generic way to provide additional information (via the URL) to the place (i.e. the activity/-ies), i.e. "#editFoo:42". You can of course re-use one place to dispatch to several activities based on the token. See the (currently not used) for ProxyPlace and ProxyListPlace in the Expenses sample for an example.

keeping History management abstracted in it’s own right

the need for Presenters to be capable of responding to History tokens

Presenters are decoupled from token managemen

> is so called REST like URLs possible ? /employees/1 This is no more or less "REST like" than the above (I assure you!); and yes it's possible (the issues then are to identify objects that are not yet persisted to the server; and of course mapping the "employees" to an EntityProxy class, representing the class+id couple in the Place, and having dedicated "find" methods to retrieve the object from the server, as without an EntityProxyId you won't be able to use RequestFactory.find()) > does it mean we have to write custom getPlace, getToken, to convert > tokens to places ? Yes. That or writing your own PlaceHistoryMapper that won't use PlaceTokenizer's at all (i.e. implement PlaceHistoryMapper in a concrete class and not use the GWT.create() magic to generate the implementation).

use the history and pass the information as parameters in the history token.

has a number of advantages provided the parameter is serializable (and small enough). For example, it could let the user bookmark the detail page of "Lady_Gaga". A bit trickier when the presenter is a dialog box, but totally doable.

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

In our app, in effect, each "parent presenter" also plays the role of "app controller"; but because we have the presenter/view dichotomy, the view exposes setSomeWidget(...) methods that the presenter calls; e.g. setHeader(...), setBody(...), setFooter(...).

> 3- what do you think of "presenter.go(container)" ? We do it the other way around: our presenters have a getView() method and the parent calls container.add((Widget) child.getView()). This is actually split between the presenter and the view, see above: view.setHeader(childPresenter.getView()) in the presenter, and containerWidget.add((Widget) child) in the view. The only "issue" with presenter.go(container) is that container must be a "simple" container, which means that when it's meant to be a dock (layout) panel, tab panel, or some other complex panel (or an absolute panel and you want to add with coordinates), you actually have to add a SimplePanel first and pass it as the "container" to the go() method. Otherwise, I can't see a problem with presenter.go(container).

navigation/ > history token inside multiple IF statements ? I'm using a very similar approach as the one in bikeshed: http://code.google.com/p/google-web-toolkit/source/browse/trunk/bikes...