[linux-audio-dev] [ot] How do GUI-libs notify the program of changes?

[Dave Robillard]

On Mon, 2006-04-10 at 16:09 +0200, Alfons Adriaensen wrote:
> On Mon, Apr 10, 2006 at 03:11:49PM +0200, Julien Claassen wrote:
> > Hi all!
> >   I know it's completely OT, but I think there maybe people here, who could
> > help me.
> >   Problem is: I'm still on my libcui (character user interface) project and I
> > wonder:
> >   I push a button, slide a slider... How does the UI notify the program of
> > this change? How do Engine and UI communicate?
> >   Please anyone: HELP ME!
> 
> Hello Julien,
> 
> This is a tricky subject, and most toolkits have their own peculiar
> methods of solving the problem.
> 
> In general terms this needs callback functions - a function supplied
> as a creation parameter to the widget, and which it will call when
> it has something to report.
> 
> In C this is quite easy to arrange. The widget is given a function
> pointer, and usually also a void* which becomes the first argument
> of the callback fucntion and points to any context the receiver wants
> to be available when called back. Other arguments depend on what the
> callback needs to report.
> 
> In C++ you will want class function members to act as callbacks, and
> here things get complicated. Since callback functions are strongly
> typed and this type depends on the class they are in, there is no single
> variable type you can put into the widget to hold the function pointer.

If you want this in C++, you definitely want to use libsigc++.

(Keyword definitely)

-DR-