Re: KDE & Companies: Ask Trolltech Anything

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Re: KDE & Companies: Ask Trolltech Anything
by Justin on Sunday 08/Jul/2001, @01:49

I think QEvent is for window-system events only (like paint, mouse, keystroke, etc), while signal/slot is for anything under the sun.

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Re: KDE & Companies: Ask Trolltech Anything
by Amir Michail on Sunday 08/Jul/2001, @02:40

Yes, that's true, but why have two completely different mechanisms? Why not have a more general mechanism that can support all kinds of tasks?

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Re: KDE & Companies: Ask Trolltech Anything
by not me on Sunday 08/Jul/2001, @03:46

I'd say that signals/slots are probably slower than QEvent by a small amount, but every little bit counts when you're processing clicks and keypresses at the toolkit level.

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Re: KDE & Companies: Ask Trolltech Anything
by Guillaume Laurent on Sunday 08/Jul/2001, @06:45

One obvious answer is performance reasons, the other is simply that event handling and signals are actually quite different in purpose.

Signals are used to "communicate" between widgets, typically when a widget needs to report about a state change. Events are things which the widget may want to handle itself.

Try figuring out how it would be if QEvents were replaced by signals or if signals were replaced by QEvent. It just won't work.

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Re: KDE & Companies: Ask Trolltech Anything
by Justin on Sunday 08/Jul/2001, @18:30

Well, signals/slots don't have to be used for widgets. That's the difference I pointed out above.

Take, for example, my project called Psi (it's a Jabber client. see: http://www.affinix.com/~justin/programs/psi/). The backend classes to handle the XML, networking, and communication to the main program all use signal/slots. There is no widget in sight. In fact, the first incarnations of Psi were all console based (requiring Qt of course, because of the signal/slots and QSocket/QXml/QString,etc). QEvents are window system notifications. Signals/slots are a really cool way for your classes to interact within your program.

-Justin

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