From: uncutstone wu <uncutstone@...>
Date: 2006-05-18T02:25:53+09:00
Subject: Re: Need help designing UI

Ryan Leavengood wrote:
> Essentially all communication between various parts of the system
> (from the OS to applications and back, from applications to their
> windows and back, from windows to the GUI components and back) is done
> via messages. A looper class is used to loop over messages coming in
> and then the handling of these messages are delegated to a handler
> class. On BeOS frequently the looper and handler are the same class.
> 
> Messages are handled first by their direct recipient (for example a
> mouse down would be handled first by the component being clicked on.)
> If the message cannot be handled by that recipient, it is passed up
> the inheritance hierarchy until it is handled. Usually messages that
> are used within an application itself are targeted directly to the
> window, and then the window can delegate to the appropriate component.
> 
> So for you example, the "Close Window" toolbar button would have a
> message with an associated CLOSE command constant, with the target of
> the message being the window. When the button is clicked, the CLOSE
> message will be sent to the window and the handling of that message
> will close the window (of course.) The nice thing about this is that
> the CLOSE message could be used from other places without having to
> change how it is handled within the window.
> 
> Ryan

I think there are two essential design patterns here, one is message
dispatcher, and the other is chain of responsibility .

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