Commit 52f5a78c authored by Bastian Ilsø's avatar Bastian Ilsø

Update hello-world.c to GtkApplication, document

parent 01d76b77
......@@ -100,7 +100,7 @@
application. Inside the activate() function we want to construct
our GTK window, so that a window is shown when the application
is launched. The call to gtk_application_window_new() will
createa a new #GtkWindow and store it inside the
create a new #GtkWindow and store it inside the
<varname>window</varname> pointer. The window will have a frame,
a title bar, and window controls depending on the platform.</para>
......@@ -165,6 +165,47 @@
<para>As seen above, example-1.c builds further upon example-0.c by adding a
button to our window, with the label "Hello World". Two new GtkWidget pointers
are declared to accomplish this, <varname>button</varname> and
<varname>button_box</varname>. The button_box variable is created to store a
#GtkButtonBox which is GTK+'s way of controlling the size and layout of buttons.
The #GtkButtonBox is created and assigned to gtk_button_box_new() which takes a
#GtkOrientation enum as parameter. The buttons which this box will contain can
either be stored horizontally or vertically but this does not matter in this
particular case as we are dealing with only one button. After initializing
button_box with horizontal orientation, the code adds the button_box widget to the
window widget using gtk_container_add().</para>
<para>Next the <varname>button</varname> variable is initialized in similar manner.
gtk_button_new_with_label() is called which returns a GtkButton to be stored inside
<varname>button</varname>. Afterwards <varname>button</varname> is added to
our <varname>button_box</varname>.
Using g_signal_connect the button is connected to a function in our app called
print_hello(), so that when the button is clicked, GTK will call this function.
As the print_hello() function does not use any data as input, NULL is passed
to it. print_hello() calls g_print() with the string "Hello World"
which will print Hello World in a terminal if the GTK application was started
from one.</para>
<para>After connecting print_hello(), another signal is connected to the "clicked" state
of the button using g_signal_connect_swapped(). This functions is similar to
a g_signal_connect() with the difference lying in how the callback function is
treated. g_signal_connect_swapped() allow you to specify what the callback
function should take as parameter by letting you pass it as data. In this case
the function being called back is gtk_widget_destroy() and the <varname>window</varname>
pointer is passed to it. This has the effect that when the button is clicked,
the whole GTK window is destroyed. In contrast if a normal g_signal_connect() were used
to connect the "clicked" signal with gtk_widget_destroy(), then the <varname>button</varname>
itself would have been destroyed, not the window.
More information about creating buttons can be found
<ulink url="">here</ulink>.
<para>The rest of the code in example-1.c is identical to example-0.c. Next
section will elaborate further on how to add several GtkWidgets to your GTK
#include <gtk/gtk.h>
/* This is a callback function. The data arguments are ignored
* in this example. More on callbacks below.
static void
print_hello (GtkWidget *widget,
gpointer data)
......@@ -10,95 +7,40 @@ print_hello (GtkWidget *widget,
g_print ("Hello World\n");
static gboolean
on_delete_event (GtkWidget *widget,
GdkEvent *event,
gpointer data)
/* If you return FALSE in the "delete_event" signal handler,
* GTK will emit the "destroy" signal. Returning TRUE means
* you don't want the window to be destroyed.
* This is useful for popping up 'are you sure you want to quit?'
* type dialogs.
g_print ("delete event occurred\n");
return TRUE;
main (int argc,
char *argv[])
static void
activate (GtkApplication *app,
gpointer user_data)
/* GtkWidget is the storage type for widgets */
GtkWidget *window;
GtkWidget *button;
GtkWidget *button_box;
/* This is called in all GTK applications. Arguments are parsed
* from the command line and are returned to the application.
gtk_init (&argc, &argv);
/* create a new window, and set its title */
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_window_set_title (GTK_WINDOW (window), "Hello");
window = gtk_application_window_new (app);
gtk_window_set_title (GTK_WINDOW (window), "Window");
gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
/* When the window emits the "delete-event" signal (which is emitted
* by GTK+ in response to an event coming from the window manager,
* usually as a result of clicking the "close" window control), we
* ask it to call the on_delete_event() function as defined above.
* The data passed to the callback function is NULL and is ignored
* in the callback function.
g_signal_connect (window, "delete-event", G_CALLBACK (on_delete_event), NULL);
button_box = gtk_button_box_new (GTK_ORIENTATION_HORIZONTAL);
gtk_container_add (GTK_CONTAINER (window), button_box);
/* Here we connect the "destroy" event to the gtk_main_quit() function.
* This signal is emitted when we call gtk_widget_destroy() on the window,
* or if we return FALSE in the "delete_event" callback.
g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
/* Sets the border width of the window. */
gtk_container_set_border_width (GTK_CONTAINER (window), 10);
/* Creates a new button with the label "Hello World". */
button = gtk_button_new_with_label ("Hello World");
/* When the button receives the "clicked" signal, it will call the
* function print_hello() passing it NULL as its argument.
* The print_hello() function is defined above.
g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
/* The g_signal_connect_swapped() function will connect the "clicked" signal
* of the button to the gtk_widget_destroy() function; instead of calling it
* using the button as its argument, it will swap it with the user data
* argument. This will cause the window to be destroyed by calling
* gtk_widget_destroy() on the window.
g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_widget_destroy), window);
gtk_container_add (GTK_CONTAINER (button_box), button);
/* This packs the button into the window. A GtkWindow inherits from GtkBin,
* which is a special container that can only have one child
gtk_container_add (GTK_CONTAINER (window), button);
/* The final step is to display this newly created widget... */
gtk_widget_show (button);
gtk_widget_show_all (window);
/* ... and the window */
gtk_widget_show (window);
main (int argc,
char **argv)
GtkApplication *app;
int status;
/* All GTK applications must have a gtk_main(). Control ends here
* and waits for an event to occur (like a key press or a mouse event),
* until gtk_main_quit() is called.
gtk_main ();
app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
status = g_application_run (G_APPLICATION (app), argc, argv);
g_object_unref (app);
return 0;
return status;
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