Re: Event Propagation problem

[lecas malecas <darkiiiiii gmail com>]

hey, maybe we should update that chapter to mention this part..

On Fri, Jan 13, 2012 at 3:57 PM, Kjell Ahlstedt
<kjell ahlstedt bredband net> wrote:
> A long reply to a long question. The most interesting part is at the end of
> the reply.
>
> The propagation of keyboard events is more complicated than the description
> in the Gtkmm tutorial shows.
> When I helped Pedro with the Keyboard Events chapter, he found this
> description:
> http://faq.pygtk.org/index.py?file=faq03.011.htp&req=show
> (If you're very interested, see bug
> https://bugzilla.gnome.org/show_bug.cgi?id=661857)
>
> The last paragraph in the pygtk FAQ reads:
>
> "Keyboard events are handled differently. When your window receives a
> keyboard event, it is first dispatched to the toplevel window, which will
> check if it matches any keyboard shortcuts. If the key press doesn't match a
> shortcut, then the event is dispatched to the child widget that currently
> has focus."
>
> Because we were not sure if that still holds (written Nov 2002), we decided
> not to mention it in the gtkmm tutorial.
>
> Now I looked in gtk+'s source code to see how events (especially keyboard
> events) are really handled.
>
> Start at gtk_main_do_event(). The description of that function is
> incomplete. It does not at all mention the most interesting part of how
> keyboard events are handled, perhaps because that happens in
> gtk_propagate_event() to which the event is usually sent. The description of
> gtk_propagate_event() is equally incomplete. It does not send keyboard
> events to the window with keyboard focus, but to the toplevel window
> (GtkWindow, Gtk::Window in gtkmm).
> gtk_propagate_event() calls gtk_widget_event(), which emits the
> key-press-event or key-release-event signal.
> GtkWindow's default handler for the key-press-event first calls
> gtk_window_activate_key(), which activates mnemonics and accelerators.
> If gtk_window_activate_key() returns TRUE, the event is considered fully
> handled.
> If gtk_window_activate_key() returns FALSE, gtk_window_propagate_key_event()
> is called, and at last the event is sent to the widget with keyboard focus,
> and propagated as described in the gtkmm tutorial.
>
> I think you actually have a chance to get the keyboard event before
> gtk_window_activate_key().
> Connect your event handler to the key-press-event signal (and perhaps also
> to key-release-event) in the toplevel widget (Gtk::Window). Connect with
> after=false. Then your event handler will be called before GtkWindow's
> default event handler, and you have a chance to mark the event fully handled
> (by returning true) before gtk_window_activate_key() is called. Example (the
> 'false' parameter is important!):
>
>  window->signal_key_press_event().connect(sigc::mem_fun(*this,
> &MyWindow::on_key_event), false);
>
> Kjell
>
> 2012-01-13 04:26, lecas malecas skrev:
>
>> Actually, I'm not sure if this would fix it, since you're using
>> accelerator keys (those keys could be checked first before the event
>> is emited in the widget?.. not sure).
>>
>> If it doesn't work, try to have the shortcuts in an event function on
>> the Gtk::Window, instead of as an accelerator.
>>
>> On Fri, Jan 13, 2012 at 1:17 AM, lecas malecas<darkiiiiii gmail com>
>>  wrote:
>>>
>>> You could try overriding the event functions (for example: virtual
>>> bool on_key_press_event (GdkEventKey* event)).
>>>
>>>
>>> On Thu, Jan 12, 2012 at 7:15 PM, Carlos Lopez Gonzalez
>>> <carloslopezgonzalez yahoo es>  wrote:
>>>>
>>>> Hi!
>>>> First of all I want to say sorry for the long post, but the existing
>>>> code is
>>>> long to explain.
>>>> According to the Event Propagation lesson from the Grkmm Programming
>>>> book,
>>>> one even that happens in a widget can be handled by it by connecting the
>>>> correspondent signal to the event handler. If the handler returns true,
>>>> the
>>>> event isn't propagated upstream to the parent containers of the widget.
>>>>
>>>> I'm having troubles obtaining the intended result:
>>>>
>>>>
>