Thank you, Jens. Yes, I created only one EventBus and was passing it along
everywhere. But I was using eventBus = new SimpleEventBus();. I should have
used :
eventBus = new ResettableEventBus(new SimpleEventBus());
But it didn't give me any error. That means, ActivityManager checks if the
instance of EventBus is a Resettable one. Otherwise it would have thrown a
compilation or runtime error at
ActivityManager activityManager = new ActivityManager(activityMapper,
clientFactory.getEventBus());
So anyway, what I also understand from your response is that if I don't
need any cleaning in my Activity, there is no need to create a new one each
time (or I could call a reset() method in start(). But then I would be
going against a commonly used pattern.
JavaScript has garbage collection? I didn't know that.
thank you!
On Sunday, February 10, 2013 1:50:49 PM UTC-5, Jens wrote:
>
> 1. I understand that Activity instances are disposable but view instances
>> are not.
>>
>> 2. As a result of a place change, my ActivityMapper creates a new
>> Activity instance:
>> if (place instanceof LoginPlace)
>> return new LoginActivity((LoginPlace) place, clientFactory);
>>
>> Question: While it is true that Activity is supposed to be disposable, is
>> it really a good idea to create a new instance instead of reusing an
>> existing one? I.e. is it better to just do clientFactory.getHomeActivity()?
>>
>
> Activities are lightweight compared to widget/views because widget/views
> need to do DOM operations to construct themselves. Most people recreate
> activities so they dont have to care about their internal state. You always
> have a clean new instance and the old instance can be garbage collected.
>
> Views/Widget on the other hand my be cached/singleton if its worth it. For
> example if you have an endless scrolling list you dont want to create list
> entry widgets all the time. If you only see 20 entries at any time you
> maybe have a list of 30 entry widgets that are reused while scrolling.
>
>
>
> Now, as per the JavaDoc documentation of Activity,
>>
>> Any handlers attached to the provided event bus will be de-registered
>> when the activity is stopped, so activities will rarely need to hold on to
>> the
>> HandlerRegistration<http://google-web-toolkit.googlecode.com/svn/javadoc/2.1/com/google/gwt/event/shared/HandlerRegistration.html>
>> instances
>> returned byEventBus.addHandler(com.google.gwt.event.shared.GwtEvent.Type,
>> H)<http://google-web-toolkit.googlecode.com/svn/javadoc/2.1/com/google/gwt/event/shared/EventBus.html#addHandler(com.google.gwt.event.shared.GwtEvent.Type,+H)>
>> .
>>
>> So, what I understand is that in the mayStop() method of my activity, I
>> don't have to do anything wrt the event handler. If the user goes back to
>> the same activity again, a new Activity instance will be created and a new
>> handler will be registered (since that code is in the constructor). The old
>> registration is automatically cleaned up.
>>
>
> The handler is only cleaned up automatically if you use the "special"
> EventBus provided in Activity.start(). The EventBus in the start() method
> is your application wide EventBus (the one you gave the ActivityManager)
> wrapped by a ResettableEventBus. Whenever you switch Activities the
> ActivityManager will reset the ResettableEventBus which causes all handlers
> being added by the activity to be deregistered.
>
>
> -- J.
>
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