Re: [gtkmm] Key Snooping / Key_Press_Event Howto?

[Jeff Gavin <jeff ezclick net>]

Andrew E. Makeev wrote:
> Jeff Gavin wrote:
>
> > I'm trying to validate an entry while the user types.  I've read all 
> > the posts on entry validation and I still don't know an answer.  I 
> > would like to create a entry that can validate a date while the user 
> > types it in, but to simplify things on the initial version, I decided 
> > to create an entry that only allows numbers to be typed in.
> >
> > Keep in mind I come from a MS/VB background (I know, yech, ptooie, 
> > gross!).
> >
> > From this experience, I have created entries that would intercept each 
> > keystroke and decide weather to accept them or not.
> >
> > For example this VB code snip would not allow the "UserCode" field to 
> > accept certain characters.  Changing the KeyAscii code to 0 prevents 
> > the entry from accepting the keystroke:
> >
> > Private Sub txtUserCode_KeyPress(KeyAscii As Integer)
> >   ' Check for invalid character and exclude them.
> >   If InStr(1, " ~`! #$%^&*()_+-={}[]\|:;<>,./?'""", Chr(KeyAscii)) > 0 
> > Then
> >     KeyAscii = 0
> >   End If
> > End Sub
> >
> > I cannot figure out how to do this with gtk+/gtkmm.  The 
> > key_press_event seemed like an obvious candidate, but it only triggers 
> > when the user presses shift/esc/ctrl.  Maybe this is not such a good 
> > name for this event if that's all it can do.  Is there a way to make 
> > all the key presses to be passed to the callback?  I'm sure someone 
> > has had to solve this type of problem before.  How did you do it?
> >
> > Best Regards,
> >
> > Jeff
> 1. Try to read tutorial and API reference about signal/event processing.

I did try, but even now after knowing the answer, I cannot find it in 
the documentation.  Where would I find this particular answer?

> 2. You have to connect to signal with parameter after=false set, like this:
>
> <widget>.signal_key_press_event ().connect (SigC::slot (<callback>), 
> false);

Thank you so much!  I knew that I must be missing something fundamental 
like this!  Here is how to register for a key_press_event (note that you 
must place false at the end):

my_entry->signal_key_press_event().connect(SigC::slot(*this,my_class::on_my_entry_key_press_event),false);

Then the callback function would look something like this:

// my_entry only allows digits 0..9 to be typed in.
// All other keystrokes are ignored.
bool my_class::on_my_entry_key_press_event (GdkEventKey* event)
{
	const static Glib::ustring s = "0123456789";
 	return (gint(s.find(event->string)) == -1);
}


> then your callback would be called before Gtk+ keypress event handling.
> Keep in mind you could stop event processing just with return value = true.

Again thanks!

Jeff