Re: updating labels when a key is stroked

[Eric Wajnberg <eric wajnberg sophia inra fr>]

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

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    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Eric Wajnberg
    Associated Professor at the
    University of Montreal (Quebec, Canada)
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