Re: Beginners question abour events

[Iago Rubio <iago rubio hispalinux es>]

El dom, 29 de 02 de 2004 a las 18:50, Douglas Phillipson escribiÃ:
> Murray Cumming wrote:
> > On Sun, 2004-02-29 at 17:03, Douglas Phillipson wrote:
> >
> > > I can't seem to find why you return TRUE, or FALSE at the end of an 
> > > event routine like:
[snip]
> > Here's the gtkmm version of the explanation:
> > http://www.gtkmm.org/gtkmm2/docs/tutorial/html/apbs06.html
>
> I understand what the difference is between returning TRUE and FALSE in 
> a handler now (thankyou for the link).  Now how do you tell which you 
> should use?  

The clue is: if you want gtk to continue to proccess the signal return
FALSE. If all the work is done in your callback return TRUE.

That's all: have gtk something to do with the signal once your callback
ends ? Return FALSE and gtk will continue to proccess it. Have gtk
nothing to do with the signal ? Return TRUE and pop this signal out the
queue.

> Example code I see like:
> [snip]
> Why is the expose event returning FALSE?  If this implies something else 
> must be done in the event mechanism, what is remaining?  Where might 
> this be documented?

Here gtk must continue to proccess the event once the draw is done to
show it. So returning FALSE you let gtk finish the job. 

> The button press event seems to be done so it returns TRUE.  Is there 
> something else I could do, or the gtk/gdk system would/could do with 
> button events if I returned FALSE?

I suposse that not too much :)

But you can check much better how this works with other signals, as the
delete_event

Once gtk gets a delete_event it kills the window or dialog receiving the
signal.

So,

delete_event(){
        return FALSE;
}

... will kill the window, but ...

delete_event(){
        return TRUE;
}

.. will push out the queue the delete_event signal and the window will
not be killed.

This way you can do:

on_window_delete_event(){
        if( everything_is_ok() ){
                return FALSE;
        }else{
                // stop processing the signal
                // I have something to do ...
                return TRUE;
        }
}


Hope this helps :)
-- 
Iago Rubio                http://www.iagorubio.com          
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