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Re: EVENT_PRO [message #73768 is a reply to message #40935]

Mon, 29 November 2010 11:40

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

David Fanning writes:

> This means that in a Catalyst application a single
> "event" might be sent to several different "event
> handlers", rather than to a single event handler,
> as happens in a strict widget program.
>
> In Catalyst you assign an "event handler" to a widget
> with the EVENT_OBJECT keyword. There is an optional
> EVENT_METHOD keyword that can be used select the actual event
> method for this event object. Otherwise, the event
> is always sent to the EventHandler method of the
> event object.

I should probably point out that "event objects" don't
have to be widgets. In fact, most of the time they
are not. If you changed a colorbar object, for example,
you might wish to update any number of image objects
with the new color information. In this case, the
event objects would be these image objects who need
to know about the colorbar "event".

There is a parallel system of "messages" in the
Catalyst Library that act in a similar way. An
object can register an "interest" in the actions of
another object and be "notified" when that action
occurs. This is really just a more specific instance
of "event handling" in objects.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		event_pro for compound widgets By: Benjamin Hornberger on Tue, 07 September 2004 10:32
		Re: EVENT_PRO By: David Fanning on Mon, 29 November 2010 11:40
		Re: EVENT_PRO By: David Fanning on Mon, 29 November 2010 11:09
		Re: EVENT_PRO By: silje on Mon, 29 November 2010 11:02
		Re: EVENT_PRO By: David Fanning on Mon, 29 November 2010 11:02
		Re: EVENT_PRO By: Paul Van Delst[1] on Mon, 29 November 2010 10:43
		Re: EVENT_PRO By: David Fanning on Mon, 29 November 2010 10:38
		Re: EVENT_PRO By: silje on Mon, 29 November 2010 09:22
		Re: EVENT_PRO By: David Fanning on Mon, 29 November 2010 08:46

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