Re: g_signal_connect_swapped

[Philippe Bertin <philippe bertin telenet be>]

Richard,

I'm also, as you are, a rather inexperienced GTK programmer, but I hope 
to still help you by the following, without immediately digging into all 
kinds of technical details :
whereever the _swapped variant is used, that is done to call a callback 
from within a widget, to a procedure that's applicable on another widget 
(or even, in most cases another widget class).

So e.g., a button press that should be calling some callback procedure 
on the window it is in, will use the _swapped variant (passing the 
window pointer as user_data argument). Doing so will make GTK's internal 
mechanics to "convert/abuse" that user_data argument's value, by putting 
it into the callback's call as it's *first* argument), so that the 
window's callback doesn't even realize it used to be the original 
widget's call's user_data argument).

Hope this helps you more than it eventually further confuses you,

Kind regards,

PhB

Richard Riley wrote:

> "Matt Hoosier" <matt hoosier gmail com> writes:
>
>  
>
> > On 11/25/06, Richard <rileyrg googlemail com> wrote:
> >    
> >
> > > Could someone explain the reason for this function
> > >
> > > "g_signal_connect_swapped"
> > >
> > > I have read the manual here:
> > >
> > > http://www.gtk.org/tutorial/x159.html
> > >
> > > where it says:
> > >
> > > ,----
> > > | g_signal_connect_swapped() is the same as g_signal_connect() except that
> > > | the instance on which the signal is emitted and data will be swapped
> > > | when calling the handler. So when using this function to connect
> > > | signals, the callback should be of the form
> > > |
> > > |
> > > | void callback_func( gpointer   callback_data,
> > > |                     ... /* other signal arguments */
> > > |                     GtkWidget *widget);
> > > |
> > > | where the object is usually a widget.
> > > `----
> > >
> > > Could anyone express this a little clearer? I (as a gtk beginner) can
> > > see no reason for it.
> > >      
> > This just means that the "widget" and "callback_data" pointers will be
> > pushed onto the call stack in the opposite order from their ordering
> > if hooked up with g_signal_connect(). If you're designing your own
> > callback function, this probably isn't useful; just use
> > g_signal_connnect() with a callback that has GObject* and gpointer
> > parameters [in that order].
> >    
>
> I can see the order has changed - it was the reason I was looking for. I
> don't currently see the point. Maybe it will become clearer as I learn
> more.
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