Re: updating labels when a key is stroked

[Bernhard Schuster <schuster bernhard googlemail com>]

Keep asking, sometimes the response delay is actually a good thing :)

A side note: depending on what version of gtk you are using, signals 
may change (i.e. gtk2 "expose_event", gtk3 "draw") so keep an eye open 
when following tutorials.

Best

Bernhard

On Fri, Aug 9, 2013 at 12:14 PM, Eric Wajnberg 
<eric wajnberg sophia inra fr> wrote:
> Ok, thanks!
>
> I'm just plain stupid. I indeed just have to collect a 
> "key_press_event" event and that's it!
>
> Sorry for disturbing the list with such a basic question (I am still 
> learning how to use gtk)..
>
> Cheers to all,
>
> Eric.
>
> Kang Hu wrote, On 09/08/2013 09:39,
> > all you need is an event filter.
> >
> > remove the 'g_timeout_add' line with the following code.
> > 0. get the gdk window of the created top-level gtk window.
> > GdkWindow 
> > <https://developer.gnome.org/gdk2/stable/gdk3-Windows.html#GdkWindow>* 
> > gtk_widget_get_window 
> > <https://developer.gnome.org/gtk3/3.8/GtkWidget.html#gtk-widget-get-window>(/|GtkWidget 
> > <https://developer.gnome.org/gtk3/3.8/GtkWidget.html> *widget|/);
> >
> >     GdkWindow* gdkwindow = gtk_widget_get_window (pWindow);
> >
> > 1. add event mask you're interested in
> > voidgdk_window_set_events 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#gdk-window-set-events>(/|GdkWindow 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#GdkWindow> 
> > *window|/,/|GdkEventMask 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Events.html#GdkEventMask> 
> > event_mask|/);
> >
> >     gdk_window_set_events (gdkwindow, GDK_KEY_PRESS_MASK);
> >
> > 2. register an event filter
> > voidgdk_window_add_filter (/|GdkWindow 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#GdkWindow> 
> > *window|/,/|GdkFilterFunc 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#GdkFilterFunc> 
> > function|/,/|gpointer 
> > <https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer> 
> > data|/);
> >    gdk_window_add_filter (gdkwindow, key_press_filter, pWindow);
> >
> > 3. write the filter function.
> >
> > GdkFilterReturn 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#GdkFilterReturn> 
> > (*GdkFilterFunc) (/|GdkXEvent 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Windows.html#GdkXEvent> 
> > *xevent|/,/|GdkEvent 
> > <https://developer.gnome.org/gdk3/3.8/gdk3-Event-Structures.html#GdkEvent> 
> > *event|/,/|gpointer 
> > <https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer> 
> > data|/); 
> >
> >    GdkFilterReturn key_press_filter (GdkXEvent* xevent, GdkEvent* 
> > event, gpointer data)
> >    {
> >                      // how to process key press events.
> >    }
> >
> >
> > On Wed, Aug 7, 2013 at 8:48 PM, Eric Wajnberg 
> > <eric wajnberg sophia inra fr <mailto:eric wajnberg sophia inra fr>> 
> > wrote:
> >
> >     Hi there,
> >
> >     I need to develop a gtk code in which a label is changed each 
> > time
> >     a key is stroked on the keyboad. I thus use g_timeout_add() to
> >     launch on a regular basis a function that listens to key strokes.
> >     Within this function, I used a combination of kbhit()/getch() to
> >     collected the stroken keys (because I do not want the user to hit
> >     the <return> key all the time) and update the label accordingly.
> >     The following code is just a try, and seems ok:
> >
> >     #include <stdlib.h>
> >     #include <stdio.h>
> >     #include <conio.h>
> >     #include <gtk/gtk.h>
> >
> >     int key=0;
> >     char string[500];
> >
> >     int main(int argc, char **argv)
> >     {
> >         /* declaration of widgets */
> >         GtkWidget *pWindow; /*main windows */
> >         GtkWidget *pLabel; /* a label */
> >
> >         void OnDestroy(GtkWidget *pWidget, gpointer pData); /*
> >     function call back destroy */
> >         gboolean update(gpointer pData); /* function called at 
> > regular
> >     intervals */
> >
> >         /* Initialisation of GTK+ */
> >         gtk_init(&argc, &argv);
> >
> >         /* creation of the main window */
> >         pWindow = gtk_window_new(GTK_WINDOW_TOPLEVEL);
> >
> >         /* parameters of the window */
> >         gtk_window_set_position(GTK_WINDOW(pWindow), 
> > GTK_WIN_POS_CENTER);
> >         gtk_window_set_default_size(GTK_WINDOW(pWindow), 300, 100);
> >         gtk_window_set_title(GTK_WINDOW(pWindow), "testing key 
> > input");
> >
> >         /* creation of the label */
> >         (void)sprintf(string,"%d",key);
> >         pLabel=gtk_label_new(string);
> >
> >         /* adding the label to the window */
> >         gtk_container_add(GTK_CONTAINER(pWindow), pLabel);
> >
> >         /* signal connexion */
> >         g_signal_connect(G_OBJECT(pWindow), "destroy",
> >     G_CALLBACK(OnDestroy), NULL);
> >
> >         /* function called at regular intervals .. */
> >         g_timeout_add((guint)1, update,(gpointer *)pLabel);
> >
> >         /* showing the window */
> >         gtk_widget_show_all(pWindow);
> >
> >         /* starting the loop */
> >         gtk_main();
> >
> >         return EXIT_SUCCESS;
> >     }
> >
> >     gboolean update(gpointer pData)
> >     {
> >         /* updating the label */
> >         if (kbhit())
> >         {
> >             key=getch();
> >             (void)sprintf(string, "%d",key);
> >             gtk_label_set_label(GTK_LABEL(pData), string);
> >         }
> >         return TRUE;
> >     }
> >
> >     void OnDestroy(GtkWidget *pWidget, gpointer pData)
> >     {
> >         /* stopping the loop */
> >         gtk_main_quit();
> >     }
> >
> >
> >
> >     The point is that this is actually not working correctly, because
> >     the keystrokes are collected on a console that is not there! In
> >     other words, the code above works well in "debug mode" (e.g., on
> >     Code::Blocks) when a debugging console is available, but not in
> >     "release mode" running without a console.
> >
> >     My question is thus: is there a way to listen to key stroked on
> >     the keyboard within a gtk application?
> >
> >     Thanks for any help on this!
> >
> >     Cheers, Eric.
> >
> >     _______________________________________________
> >     gtk-app-devel-list mailing list
> >     gtk-app-devel-list gnome org 
> > <mailto:gtk-app-devel-list gnome org>
> >     https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
> --
>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     Eric Wajnberg
>     Associated Professor at the
>     University of Montreal (Quebec, Canada)
>     I.N.R.A.
>     400 Route des Chappes, BP 167,
>     06903 Sophia Antipolis Cedex, France
>     Tel: (33-0) 4.92.38.64.47
>     Fax: (33-0) 4.92.38.65.57
>     e-mail: wajnberg sophia inra fr
>     Web page: http://www.sophia.inra.fr/perso/wajnberg/
>
>     Editor-in-Chief of BioControl, Published by Springer.
>
>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
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