Re: Pb with activity and events (using gin)

Thank you so much, Thomas. Your solution is very helpful. Though I still have three more questions:

1) In the comment to your code, it's said that a Scheduler must be also managed by GIN. Therefore, the question if it is a bad practice to use Scheduler.get(), while the rest of the project is managed by GIN? How about RootPanel.get() (or RootLayoutPanel.get()) factory calls? Seems like one must replace all no-parameter calls of that kind with injections. Correct me if I'm wrong.

2) Back to the main subject about EventBus. Actually I tried scheduler.scheduleDeferred()before I started looking for solutions. Seems like only scheduler.scheduleFinally() defers the event firing long enough to give other activities time to append their handlers withing start() method. At least in my particular case I encountered the "racing" condition between activities for header, content and other sections of my layout. Therefore, while there's no parallel computation in browser, GWT approach with deferred tasks adds some unexplainable magic to the process of debugging. I'm not even sure if I ever gonna prefer scheduleDeferred() to scheduleFinally() from now on.

3) I still need to fire events manually sometimes. Therefore I do inject EventBus instance to some of the activities. Despite the fact start() method uses different instance of EventBus, the code still works fine like if it's all one single instance. This discovery confuses me a lot, because buses are clearly different. How is it it even possible? And what might be the best practice of using EventBus with Activities&Places + GIN?

On Tuesday, June 4, 2013 3:06:28 PM UTC+4, Thomas Broyer wrote:

On Tuesday, June 4, 2013 12:46:16 PM UTC+2, Tugdual Huertas wrote:

Hi all,

i'm facing a litlle problem using places activities and events... Have tried multiple tricks but not luck .

My problem:

i try to fire an event from the activity but my widget does not catch it since its not loaded (I mean that if i fire this event once the widget's loaded everything works fine).

Here is my Gin configuration:

@Override

protected void configure()

{

   bind(EventBus.class).to(SimpleEventBus.class).asEagerSingleton();

   bind(PlaceHistoryMapper.class).to(MyPlaceHistoryMapper.class).in(Singleton.class);

   bind(ActivityMapper.class).to(MyActivityMapper.class).in(Singleton.class);

   bind(MyActivity.class);

   install(new GinFactoryModuleBuilder().build(MyActivityMapper.Factory.class));

}

@Provides

@Singleton

public PlaceController getPlaceController(EventBus eventBus)

{

   return new PlaceController(eventBus);

}

@Singleton

@Provides

public ActivityManager provideActivityManager(ActivityMapper activityMapper, EventBus eventBus)

{

   return new ActivityManager(activityMapper, eventBus);

}

in MyActivity:

@Inject

private MyWidget myWidget;

@Inject

private EventBus globalEventBus;

@Override

public void start(AcceptsOneWidget panel, EventBus eventBus)

{

   panel.setWidget(myWidget);

   MyEvent event = new MyEvent();

   event.setAction(MyEvent.Action.INIT);

   globalEventBus.fireEvent(event);

}

I also try two different ways of binding events in my widget, during onLoad and in constructor:

During onLoad:

@Inject EventBus eventBus;

@Override

protected void onLoad()

{

   handlersRegistration.add(eventBus.addHandler(MyEvent.TYPE, this));

}

In constructor:

private EventBus eventBus;

@Inject

public MyWidget(EventBus eventBus)

{

   this.eventBus = eventBus;

   // registration of handlers

   handlersRegistration = new ArrayList<HandlerRegistration>();

   // register myself has a listener of different event TYPE

   handlersRegistration.add(eventBus.addHandler(MyEvent.TYPE, this));

   

   ...

}

Am I doing something w rong or missing something?

All adds and removes of event handlers during the dispatching of an event (which is the case when the activity starts: it's in response to a PlaceChangeEvent) is deferred to after the event has been dispatched all handlers.

Events however are dispatched synchronously (so that handlers can possibly modify them and the sender take action depending on the event after the dispatching; see setWarning for PlaceChangeRequestEvent).

So you have to defer your fireEvent() call using the Scheduler:

// Assuming a Scheduler has been @Inject-ed

scheduler.scheduleFinally(new ScheduledCommand() {

  @Override

  public void execute() {

    MyEvent event = new MyEvent();

    event.setAction(MyEvent.Action.INIT);

    globalEventBus.fireEvent(event);

  }

});

It's a good rule to always assume you might be called as part of event dispatching unless you're handling UI events (click on a button, etc.) and thus always defer your event dispatching in this case.

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