Re: [AD] Button callback function (was: Grabber - options dialog box)

[Peter Wang <tjaden@xxxxxxxxxx>]

On 2002-05-21, Evert Glebbeek <eglebbk@xxxxxxxxxx> wrote:
> >
> > Can't you simply "derive" your custom button-with-callback widget from
> > the stock button ?
...
> Basically, I use
> 
> int d_button_callback(int msg, DIALOG *d, int c)
> {
>    int (*callback)(DIALOG *d) = d->dp3;
> 
>    if (msg == MSG_CLICK && callback)
>       callback(d);
>    return d_button_proc(msg, d, c);
> }
> 
> (Not sure about the callback routine type declaration - I use a typedef). 
> Right now, the return value of the callback function isn't used, but there 
> also is a more serious problem. With this setup, the callback processes 
> the message before the d_button_proc(), which in itself is trivial to fix, 
> but it will also respond to immediately when the button is clicked, while 
> it should wait until the mouse button is released.

I use this (in AGUP):

int d_agtk_push_proc(int msg, DIALOG *d, int c)
{
    int ret = D_O_K;

    d->flags |= D_EXIT;

    ret |= d_agtk_button_proc(msg, d, c);

    if (ret & D_CLOSE) {
        ret &= ~D_CLOSE;
        REDRAW(d);

        if (d->dp3)
            ret |= ((int (*)(DIALOG *))d->dp3)(d);
    }

    return ret;
}

Seems a bit hackish now that I read it :-) It makes D_EXIT unusable
for that widget type, but I think D_EXIT was only useful for
d_button_proc because it didn't support callbacks.  It would be easy
enough to remember the original D_EXIT setting and let it flow out the
return (I think).

> Obviously, modifying the way the d_button_proc() works by adding a 
> callback function could (would?) break backward compatibilty.

Yes, because dp3 is then taken away from the user.