Scaling gwt's "Contacts" (sample project) AppController with MVP

Posted by brad on Stack Overflow See other posts from Stack Overflow or by brad
Published on 2010-04-01T14:30:33Z Indexed on 2010/04/01 14:33 UTC
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I'm just learning GWT so I'm still trying to sort out all of its quirks and features. I'm reading through the example they give illustrating the MVP pattern, and I pretty much get it, except I'm wondering about one thing.

The AppController they use implements the ValueChangeHandler interface and the onValueChange method is triggered when history changes.

My problem is with this onValueChange in the AppController (i've included it below for anyone who hasn't seen the sample project). It's doing a string comparison on the history token sent in and instantiating the appropriate presenter to handle the action. This is all fine and dandy for the sample app with 3 actions, but how would one scale this to a real app with many more actions?

Sticking to this pattern would lead to a pretty large/ugly else if, but I'm still too new to GWT (and java) to infer a better pattern for larger apps.

Any help is greatly appreciated!

public class AppController implements Presenter, ValueChangeHandler<String> {

  ...

  public void onValueChange(ValueChangeEvent<String> event) {
    String token = event.getValue();

    if (token != null) {
      Presenter presenter = null;

      if (token.equals("list")) {
        presenter = new ContactsPresenter(rpcService, eventBus, new ContactsView());
      }
      else if (token.equals("add")) {
        presenter = new EditContactPresenter(rpcService, eventBus, new EditContactView());
      }
      else if (token.equals("edit")) {
        presenter = new EditContactPresenter(rpcService, eventBus, new EditContactView());
      }

      if (presenter != null) {
        presenter.go(container);
      }
    }
  } 
}

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