Thoughts on GWT, MVP and GWT-EXT

I have been working with implementing the MVP pattern while making use of the GWT-EXT library.

I was inspired by David Chandler’s technique for hide/showing DIV’s when switching between distinct views in the application. Because GWT-EXT uses a Viewport object to serve as the root panel on the page, David’s exact technique didn’t work out with GWT-EXT panels. The solution turns out to be to create a new Viewport on each change of the root view. In my case I simply implemented hide() and show() methods in my display to take care of this.

public void hide() {
 panel.setVisible(false);
 }

public void show() {
 Log.debug("in UserView.show");
 panel.setVisible(true);
 new Viewport(panel);
 }

In my case, panel represents the root panel for the view. My impression of Viewport is that the documentation is scarce and it is a mysery as to exactly how it manages the browser window. Perhaps there is more documentation in the underlying JS library but I didn’t go that far.

The other issue I’ve faced with GWT-EXT is that GWT-EXT aren’t always the same as GWT widgets and do not normally implement interfaces like HasClickHandlers, HasHTML, etc. I may work on extending GWT-EXT’s button to work with HasClickHandlers.

One handy feature of GWT-EXT’s Panel is the ability to add a Toolbar to the bottom or top. Immediately though I wanted to add a GWT Hyperlink. Here GWT-EXT expects controls added to the Toolbar class to derive from ToolbarItem. Eventually I discovered it is possible to add items to a Toolbar by DOM element:

private void initToolbar() {
 PlaceRequest placeRequestManageUsers = new PlaceRequest(UserPresenter.PLACE);
 linkManageUsers = new Hyperlink("Manager users", placeRequestManageUsers.toString());

 /**
 * call to addFill() makes toolbar right justify
 */
 toolbar.addFill();
 toolbar.addElement(linkManageUSers.getElement());
 ...
}

After so many years of programming in Struts I have to admit that programming in GWT represents a new way of thinking. Designing for the user experience that is possible with GWT is a welcome change of pace after so much page-oriented stuff in traditional Struts.