Hi again.
On Jun 24, 3:16 pm, Thomas Broyer <[email protected]> wrote:
> On 24 juin, 12:01, "[email protected]" <[email protected]>
> wrote:
>
>
>
> > Hi all.
>
> > I've been trying to get a nice setup of the best practices presented
> > at google i/o. I have something working, but a few questions.
>
> > The first one is how fine-grained do you go for the events you define?
> > Say i have events for updates in entities A and B in my model:
> > UpdatedAEvent, UpdatedBEvent. To prevent creating new event classes
> > for every entity i might add, i liked the idea of usinggenericsafter
> > looking at the source code of GWT.
>
> > Classes like:
> > public class ModelUpdatedEvent<V> extends
> > GwtEvent<ModelUpdatedHandler<V>> {
> > ...
> > private static Type<ModelUpdatedHandler<?>> TYPE;
> > ...
> > public static Type<ModelUpdatedHandler<?>> getType() {
> > if (TYPE == null) {
> > TYPE = new Type<ModelUpdatedHandler<?>>();
> > }
> > return TYPE;}
>
> I'd rather write:
> @SuppressWarning("unchecked")
> public static <V> Type<ModelUpdatedHandler<V>> getType() {
> return TYPE;
>
> }
>
> (TYPE might have to be of type Type<?>)
>
> (Given that you most probably won't use ModelUpdatedEvent without its
> TYPE, you can just initialize it in the declaration, like GWT does,
> and have getType() just "return TYPE")
>
> > But then i guess i can't use them with an event bus (the
> > HandlerManager)? I lack complete understand ofgenericsand wildcards,
> > but assuming the class doesn't know the type, this won't work right?
>
> Even if the class did use "V", it wouldn't work, becausegenericsin
> Java are hardly more than just syntactic sugar (google for
> "javagenericserasure").
>
> > eventBus.addHandler(ModelUpdatedEvent.getType(), ...)
>
> However you write ModelUpdatedEvent/ModelUpdatedHandler, you'd end up
> having all your handlers receive all ModelUpdatedEvent<?> events.
>
> The only way you could make this work is having a getType(Class<?>
> cls) returning a different Type<ModelUpdatedHandler<?>> instance for
> each class given as argument:
>
> public static <V> Type<ModelUpdatedHandler<V>> getType(Class<V> cls) {
> // do your magic here}
>
> ...
> eventBus.addHandler(ModelUpdatedEvent.getType(A.class), ...);
>
> ...or you could instead have a getTypeForA() and getTypeForB()
> methods:
> public static Type<ModelUpdatedHandler<A>> getTypeForA() { return
> TYPE_A; }
> public static Type<ModelUpdatedHandler<B>> getTypeForB() { return
> TYPE_B; }
>
> ...this wouldn't be that different from having a ModelUpdatedEvent
> subclass per "model class".
Thanks for your reply. I've done this (multiple subclasses), but was
looking for a better option.
>
> > The second point is regarding dependency injection. I got it working
> > for things implementing interfaces, to which i bind implementations.
> > But how do you go for the HandlerManager for example? I've tried
> > making it a singleton as in:
> > protected void configure() {
> > ...
> > bind(HandlerManager.class).asEagerSingleton();
> > ...
>
> > but i get "No @Inject or default constructor found for class
> > com.google.gwt.event.shared.HandlerManager".
>
> > Same if i use .in(Singleton.class). I've seen that GWT should fallback
> > to GWT.create when there's no injection available, but if i don't
> > mention the HandlerManager in my injector it also fails.
>
> ...and GWT.create() expects a default constructor.
>
> The solution IMO is to use a provider.
Provider it was (as in provider method), it worked fine.
Thanks again,
Ricardo
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