Why do I need to overide "onPlaceRequest" in every Presenter class?

I'm managing the History in my project via Places.

What I do is this:

• implement PlaceRequestHandler on top level (for example AppController),
• register it -> eventBus.addHandler(PlaceRequestEvent.getType(), this);
• implement method "onPlaceRequest" ,where i do project navigation.

I'm using GWT presenter and every presenter in my project overrides the onPlaceRequest method.

Why do I need this, when every request is handled from the top level "onPlaceRequest" method?

I will give an example:

public class AppController implements Presenter, PlaceRequestHandler
...........
public void bind()
{
  eventBus.addHandler(PlaceRequestEvent.getType(), this);
...
}
public void onPlaceRequest(PlaceRequestEvent event)
{
// here is the project navigation tree
} 

and let's take one presenter

public class SomePresenter extends Presenter<SomePresenter.Display>
{
... here some methods are overriden and 

@Override
protected void onPlaceRequest(PlaceRequest request)
{
// what should I do here? 
}
}

开发者_开发技巧What is the idea, and how I'm supposed to use it?

---

Instead of making all of your presenters extend PlaceRequestHandler and managing those events yourself, you can attach a PlaceHistoryHandler and a PlaceController to your event bus. Together, they manage the browser's history and your places for you. When you ask your PlaceController to goTo() a different place, it will stop your current activity and use a mapping of places to activities (your presenters) to choose which one to start next.

To use this technique, you need to have your presenters extend AbstractActivity. Try following through Google's tutorial about it in GWT's documentation called GWT Development with Activities and Places.