Hi everyone,
Before 2.1 I created an application that use the "old" MVP
architecture of having models, views and presenters. This worked quite
well. I'm migrating this application to use the 2.1 MVP framework now.
I've made some progress but am still getting my head around it.
This has hit me so far: in my old code, the presenter was responsible
for setting the listeners/handlers on the view/eventbus respectively.
Where appropriate handlers would be removed when the view changed so
that events are not handled more than once. (eg, I destroy my login
window once login succeeds, and I also remove the eventbus
LoginSucceededEvent handler, so after logging out there aren't two of
them listening on the eventbus)
Here is the start method of the apps' login activity:
@Override
public void start(AcceptsOneWidget panel, EventBus eventBus) {
LoginView view = clientFactory.getLoginView(); // just one instance
bindView(view); // eg, view.getButton().addClickHandler(...
bindEvents(view, eventBus); // eg, eventBus.addHandler(....
panel.setWidget(view.asWidget());
}
The LoginView is reused from the ClientFactory as the documentation
suggests. This raises two questions:
1) I would like to keep the GUI bindings outside the UI code (just as
I did in the old code where it was in the presenter). But since the
documentation suggests using a single instance of a the views, here I
would be adding more and more listeners each time the activity is
initialised (as they are in the ActivityMapper). The HelloMVP example
has the binding code in the view and allows the view to communicate
with the activity. Can this be avoided? It would help in keeping the
UI code strictly to UI and presentation. Short of implementing a
method on all views that clear its listeners I cannot think of a
better way (I would still think this to be cumbersome - its not
something you'd normally do)
2) Similar issue with eventbus handlers - I can't wrap the eventbus in
a ResettableEventBus as I don't want to wipe all handlers off the
eventbus, nor do I want to have to manually deal with each handler in
onStop of the Activity.
I could have static fields in the activity to determine whether the
binding has already been done, but that would eliminate the
possibility of a view that might for whatever reason need to be re-
created each time.
Am I looking for a generic answer around the current 2.1 MVP framework
where it doesn't exist?
thanks
Sunny
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