Group items tagged

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

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.

First, though, I think you shouldn't call it MVP. In my opinion it seems that what you're doing is MVC where the model is helped out by RPC. There is already so much variety in the meanings of this (MVP, MVC, etc...), especially with Activities and Request Factory coming into the picture that terminology is becoming important. Not because I don't know what you're describing, but because someone new to the frameworks will get thoroughly confused.

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)

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").

If you start thinking about the different kinds of viewers you can create you’ll see that most of them behave in the same way. Whether you display your list of boolean values (in this case) as a single select listbox (with one value being true at a time) or as a group of radio buttons or as a multiselect list (all selected are true) or as a group of check boxes the only thing separating the class ListBoxViewer from GroupViewer (for lack of a better name) would be what widgets they choose to use. They can both inherit SelectableListViewer which holds most of the logic and a setMultiSelect(boolean enabled) method. Later on when you want to create a table with a check box on each row that selects the row for some future action it’s just more of the same old.

So you have a ListBoxViewer that holds the listBox and has a getWidget() to give the widget to your panel.The viewer takes an instance of the interface ListBoxFormat in its constructor. The format implementation has a getValue(E element) that returns the value to display in the llistbox. The viewer has the required methods to set the values of the listbox and get a list of the currently selected values and so on. Probably along the way of what you’re planning to do next. By using viewers and formats you can do the same thing for other widgets like tables as well. So populating a table with values is as easy as tableViewer.setSource(aListOfTableRowObjects) where the objects in the list can by of any type that you can write a TableFormat for (with a getColumnValue(int column, E element) method). GlazedLists does this for the desktop (Swing and SWT/JFace). The cool thing there is that the viewer is aware of changes to the actual input list outside of the viewer, I don’t think that’s possible in GWT yet

the constructor uses an EnumTranslator to populate the labels in the ListBox. This allows you to use a standard GWT ConstantsWithLookup inteface to supply localized text for the enum values instead of the constant names. ConstantsWithLookup is just like Constants, but with the important ability to find a value dynamically without invoking a method corresponding to the property name.