Fun to Program – GTK+ GUI program

TOC

This was originally written and created around 2013 and may require to be updated. (2021)

GTK+ GUI programs

Here are some pointers to example codes for GNOME GUI:

• Beginner Gtk+ Course (August 20, 2012)
• GNOME Developer Platform Demos (These are mostly empty templates as of 2012.)

Let me record my practice codes which create executables with the following same behaviour.

First it displays a small window as:

 +----------------X
 |    Click me!   |
 |                |
 +----------------+

If you click it with the mouse pointer, it updates its display via call backfunction mechanism. For example, after 3 clicks, it displays a small window as:

 +--------------------X
 |   Hello World!     |
 |   Click count = 3  |
 +--------------------+

If you click the right top corner of window, this window is closed and program is terminated.

My first set of example codes do not use Glade while my second set of example codes use Glade for defining GUI design.

C

Let’s try to use the gtk+3.0 GUI libraries to build GUI version of a “Hello World!” program in simple C.

Source code: gui.c

#include <glib.h>
#include <glib-object.h>
#include <stdlib.h>
#include <string.h>
#include <gtk/gtk.h>

static void
hello(GtkWidget* button, gpointer self);

static void
quit(GtkWidget* button, gpointer self);

static int i;

static void
hello(GtkWidget* button, gpointer self) {
    i ++;
    gtk_button_set_label(GTK_BUTTON(button), 
        g_strdup_printf("Hello, World!\nClick count = %i", i));
}

static void
quit(GtkWidget* button, gpointer self) {
    gtk_main_quit ();
}

int
main(int argc, char ** args) {
    GtkWidget* window;
    GtkWidget* button;

    i = 0;
    g_type_init();
    gtk_init(&argc, &args);
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "My first GUI program");
    gtk_container_set_border_width(GTK_CONTAINER(window), (guint) 10);
    g_object_set(GTK_WINDOW(window), "window-position",
        GTK_WIN_POS_CENTER, NULL);
    gtk_window_set_default_size(GTK_WINDOW(window), 400, 100);
    g_signal_connect(window, "destroy", G_CALLBACK(quit), NULL);
    button = gtk_button_new_with_label("Click me!");
    g_signal_connect_data(button, "clicked", G_CALLBACK(hello), NULL, NULL, 0);
    gtk_container_add(GTK_CONTAINER(window), button);
    gtk_widget_show_all(window);
    gtk_main();
    return EXIT_SUCCESS;
}

Let’s look for the right compile and link options for the gtk+3.0 GUI libraries.

Search the development package of gtk+3.0

$ apt-cache search 'libgtk[0-9.-]*-dev'
libgtk2.0-dev - development files for the GTK+ library
libgtk-3-dev - development files for the GTK+ library

If the libgtk-3-dev package has not been installed, install it now.

Search the right *.pc file for gtk+3.0 for use with pkg-config.

Search the right *.pc file for gtk+3.0

$ dpkg -L libgtk-3-dev|grep '/pkgconfig/'
/usr/lib/x86_64-linux-gnu/pkgconfig/gdk-3.0.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gtk+-x11-3.0.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gtk+-3.0.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gdk-x11-3.0.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gtk+-unix-print-3.0.pc

Now you can obtain the right compile and link options used by gtk+3.0.

Compile and link options used by gtk+3.0

$ pkg-config --cflags --libs gtk+-3.0
-pthread -I/usr/include/gtk-3.0 -I/usr/include/atk-1.0 -I/usr/include/at-spi2-atk...

Let’s compile gui.c program with gtk+3.0.

Compilation of gui.c into the gtk+3.0 GUI program gui.

$ gcc -Wall `pkg-config --cflags --libs gtk+-3.0` -o gui gui.c
gui.c: In function ‘main’:
gui.c:33:5: warning: ‘g_type_init’ is deprecated (declared at /usr/include/glib-2...
     g_type_init();
     ^

Let’s list linked libraries to the ELF object hello with the nm command. .. Impressive … or too much.

Python

Let’s try to use the gtk+3.0 GUI libraries to build GUI version of a “Hello World!” program with simple Python.

Source code gui in Python language

#!/usr/bin/python3
from gi.repository import Gtk

class TopWindow(Gtk.Window):

    def __init__(self):
        Gtk.Window.__init__(self)
        self.title = "Hello World!"
        self.counter = 0
        self.border_width = 10
        self.set_default_size(400, 100)
        self.set_position(Gtk.WindowPosition.CENTER)
        self.button = Gtk.Button(label="Click me!")
        self.button.connect("clicked", self.on_button_clicked)
        self.add(self.button)
        self.connect("delete-event", self.on_window_destroy)

    def on_window_destroy(self, *args):
        Gtk.main_quit(*args)

    def on_button_clicked(self, widget):
        self.counter += 1
        widget.set_label("Hello, World!\nClick count = %i" % self.counter)

def main():
    window = TopWindow()
    window.show_all()
    Gtk.main()

if __name__ == '__main__':
    main()

Please note, “from gi.repository import Gtk” at the top.

Vala

Let’s try to use the gtk+3.0 GUI libraries to build GUI version of a “Hello World!” program with simple Vala. Just like the Vala examples for “CLI programs”, we present codes in 3 different styles.

Simple non-OOP style (no class)

Source code gui-1.vala in Vala language

using Gtk;

int main (string[] args) {
    Gtk.init (ref args);
    int i;

    var window = new Window ();
    window.title = "My first GUI program";
    window.border_width = 10;
    window.window_position = WindowPosition.CENTER;
    window.set_default_size (400, 100);
    window.destroy.connect (Gtk.main_quit);

    i = 0;
    var button = new Button.with_label ("Click me!");
    button.clicked.connect (() => {
        i ++;
        button.label = "Hello, World!\nClick count = %i".printf(i);
        });

    window.add (button);
    window.show_all ();

    Gtk.main ();
    return 0;
}

Let’s compile gui-1.vala to create the ELF object gui-1.

$ valac -v --pkg gtk+-3.0 gui-1.vala
/path/to/vala/gui-1.vala.c: In function ‘main’:
/path/to/vala/gui-1.vala.c:104:2: warning: ‘g_type_init’ is deprecated (declared ...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
cc -o '/path/to/vala/gui-1' '/path/to/vala/gui-1.vala.c' -pthread -I/usr/include/...

You can get the C source as:

$ valac -C --pkg gtk+-3.0 gui-1.vala
$ wc -l gui-1.vala ; wc -l gui-1.c
26 gui-1.vala
109 gui-1.c
$ cat gui-1.c |sed -e 's/       /    /g'|fold
/* gui-1.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-1.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <stdlib.h>
#include <string.h>
#include <gtk/gtk.h>

typedef struct _Block1Data Block1Data;
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_free0(var) (var = (g_free (var), NULL))

struct _Block1Data {
    int _ref_count_;
    gint i;
    GtkButton* button;
};



gint _vala_main (gchar** args, int args_length1);
static Block1Data* block1_data_ref (Block1Data* _data1_);
static void block1_data_unref (void * _userdata_);
static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
);
static void __lambda2_ (Block1Data* _data1_);
static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self);


static Block1Data* block1_data_ref (Block1Data* _data1_) {
    g_atomic_int_inc (&_data1_->_ref_count_);
    return _data1_;
}


static void block1_data_unref (void * _userdata_) {
    Block1Data* _data1_;
    _data1_ = (Block1Data*) _userdata_;
    if (g_atomic_int_dec_and_test (&_data1_->_ref_count_)) {
        _g_object_unref0 (_data1_->button);
        g_slice_free (Block1Data, _data1_);
    }
}


static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
) {
    gtk_main_quit ();
}


static void __lambda2_ (Block1Data* _data1_) {
    gint _tmp0_;
    gchar* _tmp1_ = NULL;
    gchar* _tmp2_;
    _tmp0_ = _data1_->i;
    _data1_->i = _tmp0_ + 1;
    _tmp1_ = g_strdup_printf ("Hello, World!\nClick count = %i", _data1_->i);
    _tmp2_ = _tmp1_;
    gtk_button_set_label (_data1_->button, _tmp2_);
    _g_free0 (_tmp2_);
}


static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self) {
    __lambda2_ (self);
}


gint _vala_main (gchar** args, int args_length1) {
    gint result = 0;
    Block1Data* _data1_;
    GtkWindow* _tmp0_;
    GtkWindow* window;
    GtkButton* _tmp1_;
    _data1_ = g_slice_new0 (Block1Data);
    _data1_->_ref_count_ = 1;
    gtk_init (&args_length1, &args);
    _tmp0_ = (GtkWindow*) gtk_window_new (GTK_WINDOW_TOPLEVEL);
    g_object_ref_sink (_tmp0_);
    window = _tmp0_;
    gtk_window_set_title (window, "My first GUI program");
    gtk_container_set_border_width ((GtkContainer*) window, (guint) 10);
    g_object_set (window, "window-position", GTK_WIN_POS_CENTER, NULL);
    gtk_window_set_default_size (window, 400, 100);
    g_signal_connect ((GtkWidget*) window, "destroy", (GCallback) _gtk_main_quit
_gtk_widget_destroy, NULL);
    _data1_->i = 0;
    _tmp1_ = (GtkButton*) gtk_button_new_with_label ("Click me!");
    g_object_ref_sink (_tmp1_);
    _data1_->button = _tmp1_;
    g_signal_connect_data (_data1_->button, "clicked", (GCallback) ___lambda2__g
tk_button_clicked, block1_data_ref (_data1_), (GClosureNotify) block1_data_unref
, 0);
    gtk_container_add ((GtkContainer*) window, (GtkWidget*) _data1_->button);
    gtk_widget_show_all ((GtkWidget*) window);
    gtk_main ();
    result = 0;
    _g_object_unref0 (window);
    block1_data_unref (_data1_);
    _data1_ = NULL;
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return _vala_main (argv, argc);
}

It is obvious that the Vala code is much shorter than the generated C code.

One notable logical difference from the corresponding C program example is the use of dynamically assigned object pointed by Block1Data* _data1_ and maneged by reference counting.

Since no OOP techniques are used, the resulting C code does not have GObject related macros.

OOP style (main outside of class)

Source code gui-2.vala in Vala language

using Gtk;

class Gui : Gtk.Window {

    private int i;

    public int run() {
        this.title = "My first GUI program";
        this.border_width = 10;
        this.window_position = WindowPosition.CENTER;
        this.set_default_size (400, 100);
        this.destroy.connect (Gtk.main_quit);
    
        this.i = 0;
        var button = new Button.with_label ("Click me!");
        button.clicked.connect (() => {
            this.i ++;
            button.label = "Hello, World!\nClick count = %i".printf(this.i);
            });
    
        this.add (button);
    	this.show_all ();
	return 0;
    }

}
int main (string[] args) {
    Gtk.init (ref args);

    var window = new Gui ();
    window.run();
    Gtk.main ();
    return 0;
}

TIP: The above example skips specifying GLib for the parent class since it is the default for Vala.

Let’s compile gui-2.vala to create the ELF object gui-2 and run it.

$ valac -v --pkg gtk+-3.0 gui-2.vala
/path/to/vala/gui-2.vala.c: In function ‘main’:
/path/to/vala/gui-2.vala.c:198:2: warning: ‘g_type_init’ is deprecated (declared ...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
cc -o '/path/to/vala/gui-2' '/path/to/vala/gui-2.vala.c' -pthread -I/usr/include/...

You can get the C source as:

$ valac -C --pkg gtk+-3.0 gui-2.vala
$ wc -l gui-2.vala ; wc -l gui-2.c
34 gui-2.vala
203 gui-2.c
$ cat gui-2.c |sed -e 's/       /    /g'|fold
/* gui-2.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-2.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>


#define TYPE_GUI (gui_get_type ())
#define GUI(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_GUI, Gui))
#define GUI_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_GUI, GuiClass))
#define IS_GUI(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_GUI))
#define IS_GUI_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_GUI))
#define GUI_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_GUI, GuiClass
))

typedef struct _Gui Gui;
typedef struct _GuiClass GuiClass;
typedef struct _GuiPrivate GuiPrivate;
typedef struct _Block1Data Block1Data;
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_free0(var) (var = (g_free (var), NULL))

struct _Gui {
    GtkWindow parent_instance;
    GuiPrivate * priv;
};

struct _GuiClass {
    GtkWindowClass parent_class;
};

struct _GuiPrivate {
    gint i;
};

struct _Block1Data {
    int _ref_count_;
    Gui * self;
    GtkButton* button;
};


static gpointer gui_parent_class = NULL;

GType gui_get_type (void) G_GNUC_CONST;
#define GUI_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), TYPE_GUI, GuiPriva
te))
enum  {
    GUI_DUMMY_PROPERTY
};
gint gui_run (Gui* self);
static Block1Data* block1_data_ref (Block1Data* _data1_);
static void block1_data_unref (void * _userdata_);
static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
);
static void __lambda2_ (Block1Data* _data1_);
static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self);
Gui* gui_new (void);
Gui* gui_construct (GType object_type);
static void gui_finalize (GObject* obj);
gint _vala_main (gchar** args, int args_length1);


static Block1Data* block1_data_ref (Block1Data* _data1_) {
    g_atomic_int_inc (&_data1_->_ref_count_);
    return _data1_;
}


static void block1_data_unref (void * _userdata_) {
    Block1Data* _data1_;
    _data1_ = (Block1Data*) _userdata_;
    if (g_atomic_int_dec_and_test (&_data1_->_ref_count_)) {
        Gui * self;
        self = _data1_->self;
        _g_object_unref0 (_data1_->button);
        _g_object_unref0 (self);
        g_slice_free (Block1Data, _data1_);
    }
}


static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
) {
    gtk_main_quit ();
}


static void __lambda2_ (Block1Data* _data1_) {
    Gui * self;
    gint _tmp0_;
    gint _tmp1_;
    gchar* _tmp2_ = NULL;
    gchar* _tmp3_;
    self = _data1_->self;
    _tmp0_ = self->priv->i;
    self->priv->i = _tmp0_ + 1;
    _tmp1_ = self->priv->i;
    _tmp2_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp1_);
    _tmp3_ = _tmp2_;
    gtk_button_set_label (_data1_->button, _tmp3_);
    _g_free0 (_tmp3_);
}


static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self) {
    __lambda2_ (self);
}


gint gui_run (Gui* self) {
    gint result = 0;
    Block1Data* _data1_;
    GtkButton* _tmp0_;
    g_return_val_if_fail (self != NULL, 0);
    _data1_ = g_slice_new0 (Block1Data);
    _data1_->_ref_count_ = 1;
    _data1_->self = g_object_ref (self);
    gtk_window_set_title ((GtkWindow*) self, "My first GUI program");
    gtk_container_set_border_width ((GtkContainer*) self, (guint) 10);
    g_object_set ((GtkWindow*) self, "window-position", GTK_WIN_POS_CENTER, NULL
);
    gtk_window_set_default_size ((GtkWindow*) self, 400, 100);
    g_signal_connect ((GtkWidget*) self, "destroy", (GCallback) _gtk_main_quit_g
tk_widget_destroy, NULL);
    self->priv->i = 0;
    _tmp0_ = (GtkButton*) gtk_button_new_with_label ("Click me!");
    g_object_ref_sink (_tmp0_);
    _data1_->button = _tmp0_;
    g_signal_connect_data (_data1_->button, "clicked", (GCallback) ___lambda2__g
tk_button_clicked, block1_data_ref (_data1_), (GClosureNotify) block1_data_unref
, 0);
    gtk_container_add ((GtkContainer*) self, (GtkWidget*) _data1_->button);
    gtk_widget_show_all ((GtkWidget*) self);
    result = 0;
    block1_data_unref (_data1_);
    _data1_ = NULL;
    return result;
}


Gui* gui_construct (GType object_type) {
    Gui * self = NULL;
    self = (Gui*) g_object_new (object_type, NULL);
    return self;
}


Gui* gui_new (void) {
    return gui_construct (TYPE_GUI);
}


static void gui_class_init (GuiClass * klass) {
    gui_parent_class = g_type_class_peek_parent (klass);
    g_type_class_add_private (klass, sizeof (GuiPrivate));
    G_OBJECT_CLASS (klass)->finalize = gui_finalize;
}


static void gui_instance_init (Gui * self) {
    self->priv = GUI_GET_PRIVATE (self);
}


static void gui_finalize (GObject* obj) {
    Gui * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_GUI, Gui);
    G_OBJECT_CLASS (gui_parent_class)->finalize (obj);
}


GType gui_get_type (void) {
    static volatile gsize gui_type_id__volatile = 0;
    if (g_once_init_enter (&gui_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (GuiClass), (GBaseI
nitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) gui_class_init, (GClas
sFinalizeFunc) NULL, NULL, sizeof (Gui), 0, (GInstanceInitFunc) gui_instance_ini
t, NULL };
        GType gui_type_id;
        gui_type_id = g_type_register_static (GTK_TYPE_WINDOW, "Gui", &g_define_
type_info, 0);
        g_once_init_leave (&gui_type_id__volatile, gui_type_id);
    }
    return gui_type_id__volatile;
}


gint _vala_main (gchar** args, int args_length1) {
    gint result = 0;
    Gui* _tmp0_;
    Gui* window;
    gtk_init (&args_length1, &args);
    _tmp0_ = gui_new ();
    g_object_ref_sink (_tmp0_);
    window = _tmp0_;
    gui_run (window);
    gtk_main ();
    result = 0;
    _g_object_unref0 (window);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return _vala_main (argv, argc);
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI

OOP style (main inside of class)

Source code gui-3.vala in Vala language

using Gtk;

class Gui : Gtk.Window {

    private int i;

    private int run() {
        this.title = "My first GUI program";
        this.border_width = 10;
        this.window_position = WindowPosition.CENTER;
        this.set_default_size (400, 100);
        this.destroy.connect (Gtk.main_quit);
    
        this.i = 0;
        var button = new Button.with_label ("Click me!");
        button.clicked.connect (() => {
            this.i ++;
            button.label = "Hello, World!\nClick count = %i".printf(this.i);
            });
    
        this.add (button);
    	this.show_all ();
	return 0;
    }

    public static int main (string[] args) {
        Gtk.init (ref args);
    
        var window = new Gui ();
        window.run();
        Gtk.main ();
        return 0;
    }
}

TIP: The above example skips specifying GLib for the parent class since it is the default for Vala.

Let’s compile gui-3.vala to create the ELF object gui-3 and run it.

$ valac -v --pkg gtk+-3.0 gui-3.vala
/path/to/vala/gui-3.vala.c: In function ‘main’:
/path/to/vala/gui-3.vala.c:155:2: warning: ‘g_type_init’ is deprecated (declared ...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
cc -o '/path/to/vala/gui-3' '/path/to/vala/gui-3.vala.c' -pthread -I/usr/include/...

You can get the C source as:

$ valac -C --pkg gtk+-3.0 gui-3.vala
$ wc -l gui-3.vala ; wc -l gui-3.c
34 gui-3.vala
203 gui-3.c
$ cat gui-3.c |sed -e 's/       /    /g'|fold
/* gui-3.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-3.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>


#define TYPE_GUI (gui_get_type ())
#define GUI(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_GUI, Gui))
#define GUI_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_GUI, GuiClass))
#define IS_GUI(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_GUI))
#define IS_GUI_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_GUI))
#define GUI_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_GUI, GuiClass
))

typedef struct _Gui Gui;
typedef struct _GuiClass GuiClass;
typedef struct _GuiPrivate GuiPrivate;
typedef struct _Block1Data Block1Data;
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_free0(var) (var = (g_free (var), NULL))

struct _Gui {
    GtkWindow parent_instance;
    GuiPrivate * priv;
};

struct _GuiClass {
    GtkWindowClass parent_class;
};

struct _GuiPrivate {
    gint i;
};

struct _Block1Data {
    int _ref_count_;
    Gui * self;
    GtkButton* button;
};


static gpointer gui_parent_class = NULL;

GType gui_get_type (void) G_GNUC_CONST;
#define GUI_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), TYPE_GUI, GuiPriva
te))
enum  {
    GUI_DUMMY_PROPERTY
};
static gint gui_run (Gui* self);
static Block1Data* block1_data_ref (Block1Data* _data1_);
static void block1_data_unref (void * _userdata_);
static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
);
static void __lambda2_ (Block1Data* _data1_);
static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self);
gint gui_main (gchar** args, int args_length1);
Gui* gui_new (void);
Gui* gui_construct (GType object_type);
static void gui_finalize (GObject* obj);


static Block1Data* block1_data_ref (Block1Data* _data1_) {
    g_atomic_int_inc (&_data1_->_ref_count_);
    return _data1_;
}


static void block1_data_unref (void * _userdata_) {
    Block1Data* _data1_;
    _data1_ = (Block1Data*) _userdata_;
    if (g_atomic_int_dec_and_test (&_data1_->_ref_count_)) {
        Gui * self;
        self = _data1_->self;
        _g_object_unref0 (_data1_->button);
        _g_object_unref0 (self);
        g_slice_free (Block1Data, _data1_);
    }
}


static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self
) {
    gtk_main_quit ();
}


static void __lambda2_ (Block1Data* _data1_) {
    Gui * self;
    gint _tmp0_;
    gint _tmp1_;
    gchar* _tmp2_ = NULL;
    gchar* _tmp3_;
    self = _data1_->self;
    _tmp0_ = self->priv->i;
    self->priv->i = _tmp0_ + 1;
    _tmp1_ = self->priv->i;
    _tmp2_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp1_);
    _tmp3_ = _tmp2_;
    gtk_button_set_label (_data1_->button, _tmp3_);
    _g_free0 (_tmp3_);
}


static void ___lambda2__gtk_button_clicked (GtkButton* _sender, gpointer self) {
    __lambda2_ (self);
}


static gint gui_run (Gui* self) {
    gint result = 0;
    Block1Data* _data1_;
    GtkButton* _tmp0_;
    g_return_val_if_fail (self != NULL, 0);
    _data1_ = g_slice_new0 (Block1Data);
    _data1_->_ref_count_ = 1;
    _data1_->self = g_object_ref (self);
    gtk_window_set_title ((GtkWindow*) self, "My first GUI program");
    gtk_container_set_border_width ((GtkContainer*) self, (guint) 10);
    g_object_set ((GtkWindow*) self, "window-position", GTK_WIN_POS_CENTER, NULL
);
    gtk_window_set_default_size ((GtkWindow*) self, 400, 100);
    g_signal_connect ((GtkWidget*) self, "destroy", (GCallback) _gtk_main_quit_g
tk_widget_destroy, NULL);
    self->priv->i = 0;
    _tmp0_ = (GtkButton*) gtk_button_new_with_label ("Click me!");
    g_object_ref_sink (_tmp0_);
    _data1_->button = _tmp0_;
    g_signal_connect_data (_data1_->button, "clicked", (GCallback) ___lambda2__g
tk_button_clicked, block1_data_ref (_data1_), (GClosureNotify) block1_data_unref
, 0);
    gtk_container_add ((GtkContainer*) self, (GtkWidget*) _data1_->button);
    gtk_widget_show_all ((GtkWidget*) self);
    result = 0;
    block1_data_unref (_data1_);
    _data1_ = NULL;
    return result;
}


gint gui_main (gchar** args, int args_length1) {
    gint result = 0;
    Gui* _tmp0_;
    Gui* window;
    gtk_init (&args_length1, &args);
    _tmp0_ = gui_new ();
    g_object_ref_sink (_tmp0_);
    window = _tmp0_;
    gui_run (window);
    gtk_main ();
    result = 0;
    _g_object_unref0 (window);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return gui_main (argv, argc);
}


Gui* gui_construct (GType object_type) {
    Gui * self = NULL;
    self = (Gui*) g_object_new (object_type, NULL);
    return self;
}


Gui* gui_new (void) {
    return gui_construct (TYPE_GUI);
}


static void gui_class_init (GuiClass * klass) {
    gui_parent_class = g_type_class_peek_parent (klass);
    g_type_class_add_private (klass, sizeof (GuiPrivate));
    G_OBJECT_CLASS (klass)->finalize = gui_finalize;
}


static void gui_instance_init (Gui * self) {
    self->priv = GUI_GET_PRIVATE (self);
}


static void gui_finalize (GObject* obj) {
    Gui * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_GUI, Gui);
    G_OBJECT_CLASS (gui_parent_class)->finalize (obj);
}


GType gui_get_type (void) {
    static volatile gsize gui_type_id__volatile = 0;
    if (g_once_init_enter (&gui_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (GuiClass), (GBaseI
nitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) gui_class_init, (GClas
sFinalizeFunc) NULL, NULL, sizeof (Gui), 0, (GInstanceInitFunc) gui_instance_ini
t, NULL };
        GType gui_type_id;
        gui_type_id = g_type_register_static (GTK_TYPE_WINDOW, "Gui", &g_define_
type_info, 0);
        g_once_init_leave (&gui_type_id__volatile, gui_type_id);
    }
    return gui_type_id__volatile;
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI

Glade

Let’s try to design GUI for a “Hello World!” with Glade and try to be used by the gtk+3.0 GUI libraries. For most cases, we should create clickme.glade.

GUI design XML file clickme.glade generated by Glade.

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- interface-requires gtk+ 3.0 -->
  <object class="GtkWindow" id="window1">
    <property name="can_focus">False</property>
    <property name="border_width">10</property>
    <property name="title" translatable="yes">My first GUI program</property>
    <property name="window_position">center-always</property>
    <property name="default_width">400</property>
    <property name="default_height">100</property>
    <signal name="destroy" handler="on_window1_destroy" swapped="no"/>
    <child>
      <object class="GtkButton" id="button1">
        <property name="label" translatable="yes">Click me!</property>
        <property name="use_action_appearance">False</property>
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="receives_default">False</property>
        <property name="use_action_appearance">False</property>
        <signal name="clicked" handler="on_button1_clicked" swapped="no"/>
      </object>
    </child>
  </object>
</interface>

TIP: You can check this by “glade clickme.glade”.

For Vala, the Gtk.Builder’s signal auto-connection mechanism uses the C name. The CamelCase namespace and class name prefix for the callback method name is converted to the lower_case C name prefix.

So for such cases as described later, we create clickme-ext.glade, instead.

Alternative GUI design XML file clickme-ext.glade generated by Glade.

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- interface-requires gtk+ 3.0 -->
  <object class="GtkWindow" id="window1">
    <property name="can_focus">False</property>
    <property name="border_width">10</property>
    <property name="title" translatable="yes">My first GUI program</property>
    <property name="window_position">center-always</property>
    <property name="default_width">400</property>
    <property name="default_height">100</property>
    <signal name="destroy" handler="hello_world_on_window1_destroy" swapped="no"/>
    <child>
      <object class="GtkButton" id="button1">
        <property name="label" translatable="yes">Click me!</property>
        <property name="use_action_appearance">False</property>
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="receives_default">False</property>
        <property name="use_action_appearance">False</property>
        <signal name="clicked" handler="hello_world_on_button1_clicked" swapped="no"/>
      </object>
    </child>
  </object>
</interface>

TIP: The class name prefix “HelloWorld.” is converted to the C name prefix “hello_world_” in the Glade XML file used by the Gtk.Builder.

C with Glade

Let’s try to use the gtk+3.0 GUI libraries and Glade generated XML file to build GUI version of a “Hello World!” program in C.

Source code: gui.c

#include <gtk/gtk.h>

static int i;

static void 
on_window1_destroy (GtkWidget *object, gpointer user_data)
{
    gtk_main_quit ();
}

static void
hello(GtkWidget* button, gpointer self) {
    i ++;
    gtk_button_set_label(GTK_BUTTON(button), 
        g_strdup_printf("Hello, World!\nClick count = %i", i));
}

int
main (int argc, char *argv[])
{
    GtkBuilder      *builder; 
    GtkWidget       *window;
    GtkWidget       *button;

    gtk_init (&argc, &argv);
    i = 0;
    builder = gtk_builder_new ();
    gtk_builder_add_from_file (builder, "clickme.glade", NULL);
    window = GTK_WIDGET (gtk_builder_get_object (builder, "window1"));
    g_signal_connect (window, "destroy", (GCallback) on_window1_destroy, NULL);
    button = GTK_WIDGET (gtk_builder_get_object (builder, "button1"));
    g_signal_connect (button, "clicked", (GCallback) hello, NULL);
    g_object_unref (G_OBJECT (builder));
        
    gtk_widget_show (window);                
    gtk_main ();

    return EXIT_SUCCESS;
}

Let’s compile gui.c program with gtk+3.0.

Compilation of gui.c into the gtk+3.0 GUI program gui.

$ gcc -Wall `pkg-config --cflags --libs gtk+-3.0` -o gui gui.c
gui.c: In function ‘main’:
gui.c:38:12: error: ‘EXIT_SUCCESS’ undeclared (first use in this function)
     return EXIT_SUCCESS;
            ^
gui.c:38:12: note: each undeclared identifier is reported only once for each func...
gui.c:39:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

Let’s list linked libraries to the ELF object hello with the nm command. .. Impressive … or too much.

Python with Glade

Let’s try to use the gtk+3.0 GUI libraries to build GUI program with Python.

Source code gui in Python language

#!/usr/bin/python3
from gi.repository import Gtk

class Handler:
    def __init__(self, *args):
        self.counter = 0

    def on_window1_destroy(self, *args):
        Gtk.main_quit(*args)

    def on_button1_clicked(self, widget):
        self.counter += 1
        widget.set_label("Hello, World!\nClick count = %i" % self.counter)

def main():
    builder = Gtk.Builder()
    builder.add_from_file("clickme.glade")
    builder.connect_signals(Handler())
    window = builder.get_object("window1")
    window.show_all()
    Gtk.main()

if __name__ == '__main__':
    main()

TIP: The content of the “class Handler:” class provides the callback handlers.

Vala with Glade

Let’s try to use the gtk+3.0 GUI libraries to build GUI version of a “Hello World!” program in Vala with the Glade generated GUI definition XML configuration file.

TIP: You need to specify the additional gmodule module to the Vala compiler option as “--pkg gmodule-2.0”. This enables the dynamic loading of methods based on the glade XML data during the program execution.

Simple non-OOP style (no class)

Source code gui-1.vala in Vala language

using Gtk;

int i;

public void on_button1_clicked (Button button) {
    i += 1;
    button.label = "Hello, World!\nClick count = %i".printf(i);
}

public void on_window1_destroy (Window window) {
    Gtk.main_quit ();
}

int main (string[] args) {     
    Gtk.init (ref args);
    i = 0;
    try {
        var builder = new Builder ();
        builder.add_from_file ("clickme.glade");
        builder.connect_signals (null);
        var window = builder.get_object ("window1") as Window;
        window.show_all ();
    } catch (Error e) {
        stderr.printf ("Could not load UI: %s\n", e.message);
        return 1;
    } 
    Gtk.main ();
    return 0;
}

Since no namespace nor class isused, simple “clickme.glade” is used here.

Let’s compile gui-1.vala to create the ELF object gui-1.

$ valac -v --pkg gtk+-3.0 --pkg gmodule-2.0 gui-1.vala
/path/to/vala-glade/gui-1.vala.c: In function ‘main’:
/path/to/vala-glade/gui-1.vala.c:118:2: warning: ‘g_type_init’ is deprecated (dec...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gmodule-2.0.vapi'
cc -o '/path/to/vala-glade/gui-1' '/path/to/vala-glade/gui-1.vala.c' -pthread -I/...

You can get the C source as:

$ valac -C --pkg gtk+-3.0 --pkg gmodule-2.0 gui-1.vala
$ wc -l gui-1.vala ; wc -l gui-1.c
29 gui-1.vala
123 gui-1.c
$ cat gui-1.c |sed -e 's/       /    /g'|fold
/* gui-1.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-1.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#define _g_free0(var) (var = (g_free (var), NULL))
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_error_free0(var) ((var == NULL) ? NULL : (var = (g_error_free (var),
NULL)))


extern gint i;
gint i = 0;

void on_button1_clicked (GtkButton* button);
void on_window1_destroy (GtkWindow* window);
gint _vala_main (gchar** args, int args_length1);


void on_button1_clicked (GtkButton* button) {
    gint _tmp0_;
    GtkButton* _tmp1_;
    gint _tmp2_;
    gchar* _tmp3_ = NULL;
    gchar* _tmp4_;
    g_return_if_fail (button != NULL);
    _tmp0_ = i;
    i = _tmp0_ + 1;
    _tmp1_ = button;
    _tmp2_ = i;
    _tmp3_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp2_);
    _tmp4_ = _tmp3_;
    gtk_button_set_label (_tmp1_, _tmp4_);
    _g_free0 (_tmp4_);
}


void on_window1_destroy (GtkWindow* window) {
    g_return_if_fail (window != NULL);
    gtk_main_quit ();
}


static gpointer _g_object_ref0 (gpointer self) {
    return self ? g_object_ref (self) : NULL;
}


gint _vala_main (gchar** args, int args_length1) {
    gint result = 0;
    GError * _inner_error_ = NULL;
    gtk_init (&args_length1, &args);
    i = 0;
    {
        GtkBuilder* _tmp0_;
        GtkBuilder* builder;
        GtkBuilder* _tmp1_;
        GtkBuilder* _tmp2_;
        GtkBuilder* _tmp3_;
        GObject* _tmp4_ = NULL;
        GtkWindow* _tmp5_;
        GtkWindow* window;
        GtkWindow* _tmp6_;
        _tmp0_ = gtk_builder_new ();
        builder = _tmp0_;
        _tmp1_ = builder;
        gtk_builder_add_from_file (_tmp1_, "clickme.glade", &_inner_error_);
        if (_inner_error_ != NULL) {
            _g_object_unref0 (builder);
            goto __catch0_g_error;
        }
        _tmp2_ = builder;
        gtk_builder_connect_signals (_tmp2_, NULL);
        _tmp3_ = builder;
        _tmp4_ = gtk_builder_get_object (_tmp3_, "window1");
        _tmp5_ = _g_object_ref0 (G_TYPE_CHECK_INSTANCE_TYPE (_tmp4_, GTK_TYPE_WI
NDOW) ? ((GtkWindow*) _tmp4_) : NULL);
        window = _tmp5_;
        _tmp6_ = window;
        gtk_widget_show_all ((GtkWidget*) _tmp6_);
        _g_object_unref0 (window);
        _g_object_unref0 (builder);
    }
    goto __finally0;
    __catch0_g_error:
    {
        GError* e = NULL;
        FILE* _tmp7_;
        GError* _tmp8_;
        const gchar* _tmp9_;
        e = _inner_error_;
        _inner_error_ = NULL;
        _tmp7_ = stderr;
        _tmp8_ = e;
        _tmp9_ = _tmp8_->message;
        fprintf (_tmp7_, "Could not load UI: %s\n", _tmp9_);
        result = 1;
        _g_error_free0 (e);
        return result;
    }
    __finally0:
    if (_inner_error_ != NULL) {
        g_critical ("file %s: line %d: uncaught error: %s (%s, %d)", __FILE__, _
_LINE__, _inner_error_->message, g_quark_to_string (_inner_error_->domain), _inn
er_error_->code);
        g_clear_error (&_inner_error_);
        return 0;
    }
    gtk_main ();
    result = 0;
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return _vala_main (argv, argc);
}

It is obvious that the Vala code is much shorter than the generated C code.

One notable logical difference from the corresponding C program example is the use of dynamically assigned object pointed by Block1Data* _data1_ and maneged by reference counting.

Since no OOP techniques are used, the resulting C code does not have GObject related macros.

OOP style (main outside of class, callback as static)

Source code gui-2.vala in Vala language

using Gtk;

class HelloWorld : Object {

    private static int i;

    public static void on_button1_clicked (Button button) {
        i += 1;
        button.label = "Hello, World!\nClick count = %i".printf(i);
    }

    public static void on_window1_destroy (Window window) {
        Gtk.main_quit ();
    }

    public int run (string[] args) {     
        i = 0;
        try {
            var builder = new Builder ();
            builder.add_from_file ("clickme-ext.glade");
            var window = builder.get_object ("window1") as Window;
            builder.connect_signals (builder);
            window.show_all ();
        } catch (Error e) {
            stderr.printf ("Could not load UI: %s\n", e.message);
            return 1;
        } 
        return 0;
    }
}
int main (string[] args) {     
    Gtk.init (ref args);
    var h = new HelloWorld();
    h.run(args);
    Gtk.main ();
    return 0;
}

Since class is isused, “clickme-ext.glade” is used here.

Although you see compiler warnings like “warning: method ... never used”, do not worry. They are used via Gtk.Builder callback mechanism.

Let’s compile gui-2.vala to create the ELF object gui-2 and run it.

$ valac -v --pkg gtk+-3.0 --pkg gmodule-2.0 gui-2.vala
gui-2.vala:7.5-7.41: warning: method `HelloWorld.on_button1_clicked' never used
    public static void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-2.vala:12.5-12.41: warning: method `HelloWorld.on_window1_destroy' never used...
    public static void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/path/to/vala-glade/gui-2.vala.c: In function ‘main’:
/path/to/vala-glade/gui-2.vala.c:208:2: warning: ‘g_type_init’ is deprecated (dec...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gmodule-2.0.vapi'
cc -o '/path/to/vala-glade/gui-2' '/path/to/vala-glade/gui-2.vala.c' -pthread -I/...
Compilation succeeded - 2 warning(s)

You can get the C source as:

$ valac -C --pkg gtk+-3.0 --pkg gmodule-2.0 gui-2.vala
gui-2.vala:7.5-7.41: warning: method `HelloWorld.on_button1_clicked' never used
    public static void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-2.vala:12.5-12.41: warning: method `HelloWorld.on_window1_destroy' never used...
    public static void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Compilation succeeded - 2 warning(s)
$ wc -l gui-2.vala ; wc -l gui-2.c
38 gui-2.vala
213 gui-2.c
$ cat gui-2.c |sed -e 's/       /    /g'|fold
/* gui-2.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-2.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>


#define TYPE_HELLO_WORLD (hello_world_get_type ())
#define HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_HELLO_WORLD, H
elloWorld))
#define HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_HELLO_W
ORLD, HelloWorldClass))
#define IS_HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_HELLO_WORLD
))
#define IS_HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_HELL
O_WORLD))
#define HELLO_WORLD_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_HELLO
_WORLD, HelloWorldClass))

typedef struct _HelloWorld HelloWorld;
typedef struct _HelloWorldClass HelloWorldClass;
typedef struct _HelloWorldPrivate HelloWorldPrivate;
#define _g_free0(var) (var = (g_free (var), NULL))
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_error_free0(var) ((var == NULL) ? NULL : (var = (g_error_free (var),
NULL)))

struct _HelloWorld {
    GObject parent_instance;
    HelloWorldPrivate * priv;
};

struct _HelloWorldClass {
    GObjectClass parent_class;
};


static gpointer hello_world_parent_class = NULL;
static gint hello_world_i;
static gint hello_world_i = 0;

GType hello_world_get_type (void) G_GNUC_CONST;
enum  {
    HELLO_WORLD_DUMMY_PROPERTY
};
void hello_world_on_button1_clicked (GtkButton* button);
void hello_world_on_window1_destroy (GtkWindow* window);
gint hello_world_run (HelloWorld* self, gchar** args, int args_length1);
HelloWorld* hello_world_new (void);
HelloWorld* hello_world_construct (GType object_type);
static void hello_world_finalize (GObject* obj);
gint _vala_main (gchar** args, int args_length1);


void hello_world_on_button1_clicked (GtkButton* button) {
    gint _tmp0_;
    GtkButton* _tmp1_;
    gint _tmp2_;
    gchar* _tmp3_ = NULL;
    gchar* _tmp4_;
    g_return_if_fail (button != NULL);
    _tmp0_ = hello_world_i;
    hello_world_i = _tmp0_ + 1;
    _tmp1_ = button;
    _tmp2_ = hello_world_i;
    _tmp3_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp2_);
    _tmp4_ = _tmp3_;
    gtk_button_set_label (_tmp1_, _tmp4_);
    _g_free0 (_tmp4_);
}


void hello_world_on_window1_destroy (GtkWindow* window) {
    g_return_if_fail (window != NULL);
    gtk_main_quit ();
}


static gpointer _g_object_ref0 (gpointer self) {
    return self ? g_object_ref (self) : NULL;
}


gint hello_world_run (HelloWorld* self, gchar** args, int args_length1) {
    gint result = 0;
    GError * _inner_error_ = NULL;
    g_return_val_if_fail (self != NULL, 0);
    hello_world_i = 0;
    {
        GtkBuilder* _tmp0_;
        GtkBuilder* builder;
        GtkBuilder* _tmp1_;
        GtkBuilder* _tmp2_;
        GObject* _tmp3_ = NULL;
        GtkWindow* _tmp4_;
        GtkWindow* window;
        GtkBuilder* _tmp5_;
        GtkBuilder* _tmp6_;
        GtkWindow* _tmp7_;
        _tmp0_ = gtk_builder_new ();
        builder = _tmp0_;
        _tmp1_ = builder;
        gtk_builder_add_from_file (_tmp1_, "clickme-ext.glade", &_inner_error_);
        if (_inner_error_ != NULL) {
            _g_object_unref0 (builder);
            goto __catch0_g_error;
        }
        _tmp2_ = builder;
        _tmp3_ = gtk_builder_get_object (_tmp2_, "window1");
        _tmp4_ = _g_object_ref0 (G_TYPE_CHECK_INSTANCE_TYPE (_tmp3_, GTK_TYPE_WI
NDOW) ? ((GtkWindow*) _tmp3_) : NULL);
        window = _tmp4_;
        _tmp5_ = builder;
        _tmp6_ = builder;
        gtk_builder_connect_signals (_tmp5_, _tmp6_);
        _tmp7_ = window;
        gtk_widget_show_all ((GtkWidget*) _tmp7_);
        _g_object_unref0 (window);
        _g_object_unref0 (builder);
    }
    goto __finally0;
    __catch0_g_error:
    {
        GError* e = NULL;
        FILE* _tmp8_;
        GError* _tmp9_;
        const gchar* _tmp10_;
        e = _inner_error_;
        _inner_error_ = NULL;
        _tmp8_ = stderr;
        _tmp9_ = e;
        _tmp10_ = _tmp9_->message;
        fprintf (_tmp8_, "Could not load UI: %s\n", _tmp10_);
        result = 1;
        _g_error_free0 (e);
        return result;
    }
    __finally0:
    if (_inner_error_ != NULL) {
        g_critical ("file %s: line %d: uncaught error: %s (%s, %d)", __FILE__, _
_LINE__, _inner_error_->message, g_quark_to_string (_inner_error_->domain), _inn
er_error_->code);
        g_clear_error (&_inner_error_);
        return 0;
    }
    result = 0;
    return result;
}


HelloWorld* hello_world_construct (GType object_type) {
    HelloWorld * self = NULL;
    self = (HelloWorld*) g_object_new (object_type, NULL);
    return self;
}


HelloWorld* hello_world_new (void) {
    return hello_world_construct (TYPE_HELLO_WORLD);
}


static void hello_world_class_init (HelloWorldClass * klass) {
    hello_world_parent_class = g_type_class_peek_parent (klass);
    G_OBJECT_CLASS (klass)->finalize = hello_world_finalize;
}


static void hello_world_instance_init (HelloWorld * self) {
}


static void hello_world_finalize (GObject* obj) {
    HelloWorld * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_HELLO_WORLD, HelloWorld);
    G_OBJECT_CLASS (hello_world_parent_class)->finalize (obj);
}


GType hello_world_get_type (void) {
    static volatile gsize hello_world_type_id__volatile = 0;
    if (g_once_init_enter (&hello_world_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (HelloWorldClass),
(GBaseInitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) hello_world_cla
ss_init, (GClassFinalizeFunc) NULL, NULL, sizeof (HelloWorld), 0, (GInstanceInit
Func) hello_world_instance_init, NULL };
        GType hello_world_type_id;
        hello_world_type_id = g_type_register_static (G_TYPE_OBJECT, "HelloWorld
", &g_define_type_info, 0);
        g_once_init_leave (&hello_world_type_id__volatile, hello_world_type_id);
    }
    return hello_world_type_id__volatile;
}


gint _vala_main (gchar** args, int args_length1) {
    gint result = 0;
    HelloWorld* _tmp0_;
    HelloWorld* h;
    gchar** _tmp1_;
    gint _tmp1__length1;
    gtk_init (&args_length1, &args);
    _tmp0_ = hello_world_new ();
    h = _tmp0_;
    _tmp1_ = args;
    _tmp1__length1 = args_length1;
    hello_world_run (h, _tmp1_, _tmp1__length1);
    gtk_main ();
    result = 0;
    _g_object_unref0 (h);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return _vala_main (argv, argc);
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI

OOP style (main outside of class, callback as instance)

Source code gui-3.vala in Vala language

using Gtk;

class HelloWorld : Object {

    private int i;

    [CCode (instance_pos = -1)]
    public void on_button1_clicked (Button button) {
        this.i += 1;
        button.label = "Hello, World!\nClick count = %i".printf(this.i);
    }

    [CCode (instance_pos = -1)]
    public void on_window1_destroy (Window window) {
        Gtk.main_quit ();
    }

    public int run (string[] args) {     
        this.i = 0;
        try {
            var builder = new Builder ();
            builder.add_from_file ("clickme-ext.glade");
            var window = builder.get_object ("window1") as Window;
            builder.connect_signals (builder);
            window.show_all ();
        } catch (Error e) {
            stderr.printf ("Could not load UI: %s\n", e.message);
            return 1;
        } 
        return 0;
    }
}
int main (string[] args) {     
    Gtk.init (ref args);
    var h = new HelloWorld();
    h.run(args);
    Gtk.main ();
    return 0;
}

Since class is isused, “clickme-ext.glade” is used here.

Although you see compiler warnings like “warning: method ... never used”, do not worry. They are used via Gtk.Builder callback mechanism.

Please make sure to use “[CCode (instance_pos = -1)]” when using instance methods instead of static methods as callback handlers for the Gtk.Builder’s signal auto-connection mechanism.

Let’s compile gui-3.vala to create the ELF object gui-3 and run it.

$ valac -v --pkg gtk+-3.0 --pkg gmodule-2.0 gui-3.vala
gui-3.vala:8.5-8.34: warning: method `HelloWorld.on_button1_clicked' never used
    public void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-3.vala:14.5-14.34: warning: method `HelloWorld.on_window1_destroy' never used...
    public void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/path/to/vala-glade/gui-3.vala.c: In function ‘main’:
/path/to/vala-glade/gui-3.vala.c:215:2: warning: ‘g_type_init’ is deprecated (dec...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gmodule-2.0.vapi'
cc -o '/path/to/vala-glade/gui-3' '/path/to/vala-glade/gui-3.vala.c' -pthread -I/...
Compilation succeeded - 2 warning(s)

You can get the C source as:

$ valac -C --pkg gtk+-3.0 --pkg gmodule-2.0 gui-3.vala
gui-3.vala:8.5-8.34: warning: method `HelloWorld.on_button1_clicked' never used
    public void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-3.vala:14.5-14.34: warning: method `HelloWorld.on_window1_destroy' never used...
    public void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Compilation succeeded - 2 warning(s)
$ wc -l gui-3.vala ; wc -l gui-3.c
40 gui-3.vala
220 gui-3.c
$ cat gui-3.c |sed -e 's/       /    /g'|fold
/* gui-3.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-3.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>


#define TYPE_HELLO_WORLD (hello_world_get_type ())
#define HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_HELLO_WORLD, H
elloWorld))
#define HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_HELLO_W
ORLD, HelloWorldClass))
#define IS_HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_HELLO_WORLD
))
#define IS_HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_HELL
O_WORLD))
#define HELLO_WORLD_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_HELLO
_WORLD, HelloWorldClass))

typedef struct _HelloWorld HelloWorld;
typedef struct _HelloWorldClass HelloWorldClass;
typedef struct _HelloWorldPrivate HelloWorldPrivate;
#define _g_free0(var) (var = (g_free (var), NULL))
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_error_free0(var) ((var == NULL) ? NULL : (var = (g_error_free (var),
NULL)))

struct _HelloWorld {
    GObject parent_instance;
    HelloWorldPrivate * priv;
};

struct _HelloWorldClass {
    GObjectClass parent_class;
};

struct _HelloWorldPrivate {
    gint i;
};


static gpointer hello_world_parent_class = NULL;

GType hello_world_get_type (void) G_GNUC_CONST;
#define HELLO_WORLD_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), TYPE_HELLO
_WORLD, HelloWorldPrivate))
enum  {
    HELLO_WORLD_DUMMY_PROPERTY
};
void hello_world_on_button1_clicked (GtkButton* button, HelloWorld* self);
void hello_world_on_window1_destroy (GtkWindow* window, HelloWorld* self);
gint hello_world_run (HelloWorld* self, gchar** args, int args_length1);
HelloWorld* hello_world_new (void);
HelloWorld* hello_world_construct (GType object_type);
static void hello_world_finalize (GObject* obj);
gint _vala_main (gchar** args, int args_length1);


void hello_world_on_button1_clicked (GtkButton* button, HelloWorld* self) {
    gint _tmp0_;
    GtkButton* _tmp1_;
    gint _tmp2_;
    gchar* _tmp3_ = NULL;
    gchar* _tmp4_;
    g_return_if_fail (self != NULL);
    g_return_if_fail (button != NULL);
    _tmp0_ = self->priv->i;
    self->priv->i = _tmp0_ + 1;
    _tmp1_ = button;
    _tmp2_ = self->priv->i;
    _tmp3_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp2_);
    _tmp4_ = _tmp3_;
    gtk_button_set_label (_tmp1_, _tmp4_);
    _g_free0 (_tmp4_);
}


void hello_world_on_window1_destroy (GtkWindow* window, HelloWorld* self) {
    g_return_if_fail (self != NULL);
    g_return_if_fail (window != NULL);
    gtk_main_quit ();
}


static gpointer _g_object_ref0 (gpointer self) {
    return self ? g_object_ref (self) : NULL;
}


gint hello_world_run (HelloWorld* self, gchar** args, int args_length1) {
    gint result = 0;
    GError * _inner_error_ = NULL;
    g_return_val_if_fail (self != NULL, 0);
    self->priv->i = 0;
    {
        GtkBuilder* _tmp0_;
        GtkBuilder* builder;
        GtkBuilder* _tmp1_;
        GtkBuilder* _tmp2_;
        GObject* _tmp3_ = NULL;
        GtkWindow* _tmp4_;
        GtkWindow* window;
        GtkBuilder* _tmp5_;
        GtkBuilder* _tmp6_;
        GtkWindow* _tmp7_;
        _tmp0_ = gtk_builder_new ();
        builder = _tmp0_;
        _tmp1_ = builder;
        gtk_builder_add_from_file (_tmp1_, "clickme-ext.glade", &_inner_error_);
        if (_inner_error_ != NULL) {
            _g_object_unref0 (builder);
            goto __catch0_g_error;
        }
        _tmp2_ = builder;
        _tmp3_ = gtk_builder_get_object (_tmp2_, "window1");
        _tmp4_ = _g_object_ref0 (G_TYPE_CHECK_INSTANCE_TYPE (_tmp3_, GTK_TYPE_WI
NDOW) ? ((GtkWindow*) _tmp3_) : NULL);
        window = _tmp4_;
        _tmp5_ = builder;
        _tmp6_ = builder;
        gtk_builder_connect_signals (_tmp5_, _tmp6_);
        _tmp7_ = window;
        gtk_widget_show_all ((GtkWidget*) _tmp7_);
        _g_object_unref0 (window);
        _g_object_unref0 (builder);
    }
    goto __finally0;
    __catch0_g_error:
    {
        GError* e = NULL;
        FILE* _tmp8_;
        GError* _tmp9_;
        const gchar* _tmp10_;
        e = _inner_error_;
        _inner_error_ = NULL;
        _tmp8_ = stderr;
        _tmp9_ = e;
        _tmp10_ = _tmp9_->message;
        fprintf (_tmp8_, "Could not load UI: %s\n", _tmp10_);
        result = 1;
        _g_error_free0 (e);
        return result;
    }
    __finally0:
    if (_inner_error_ != NULL) {
        g_critical ("file %s: line %d: uncaught error: %s (%s, %d)", __FILE__, _
_LINE__, _inner_error_->message, g_quark_to_string (_inner_error_->domain), _inn
er_error_->code);
        g_clear_error (&_inner_error_);
        return 0;
    }
    result = 0;
    return result;
}


HelloWorld* hello_world_construct (GType object_type) {
    HelloWorld * self = NULL;
    self = (HelloWorld*) g_object_new (object_type, NULL);
    return self;
}


HelloWorld* hello_world_new (void) {
    return hello_world_construct (TYPE_HELLO_WORLD);
}


static void hello_world_class_init (HelloWorldClass * klass) {
    hello_world_parent_class = g_type_class_peek_parent (klass);
    g_type_class_add_private (klass, sizeof (HelloWorldPrivate));
    G_OBJECT_CLASS (klass)->finalize = hello_world_finalize;
}


static void hello_world_instance_init (HelloWorld * self) {
    self->priv = HELLO_WORLD_GET_PRIVATE (self);
}


static void hello_world_finalize (GObject* obj) {
    HelloWorld * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_HELLO_WORLD, HelloWorld);
    G_OBJECT_CLASS (hello_world_parent_class)->finalize (obj);
}


GType hello_world_get_type (void) {
    static volatile gsize hello_world_type_id__volatile = 0;
    if (g_once_init_enter (&hello_world_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (HelloWorldClass),
(GBaseInitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) hello_world_cla
ss_init, (GClassFinalizeFunc) NULL, NULL, sizeof (HelloWorld), 0, (GInstanceInit
Func) hello_world_instance_init, NULL };
        GType hello_world_type_id;
        hello_world_type_id = g_type_register_static (G_TYPE_OBJECT, "HelloWorld
", &g_define_type_info, 0);
        g_once_init_leave (&hello_world_type_id__volatile, hello_world_type_id);
    }
    return hello_world_type_id__volatile;
}


gint _vala_main (gchar** args, int args_length1) {
    gint result = 0;
    HelloWorld* _tmp0_;
    HelloWorld* h;
    gchar** _tmp1_;
    gint _tmp1__length1;
    gtk_init (&args_length1, &args);
    _tmp0_ = hello_world_new ();
    h = _tmp0_;
    _tmp1_ = args;
    _tmp1__length1 = args_length1;
    hello_world_run (h, _tmp1_, _tmp1__length1);
    gtk_main ();
    result = 0;
    _g_object_unref0 (h);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return _vala_main (argv, argc);
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI

OOP style (main inside of class, callback as static)

Source code gui-4.vala in Vala language

using Gtk;

class HelloWorld : Object {

    private static int i;

    public static void on_button1_clicked (Button button) {
        i += 1;
        button.label = "Hello, World!\nClick count = %i".printf(i);
    }

    public static void on_window1_destroy (Window window) {
        Gtk.main_quit ();
    }

    private int run (string[] args) {     
        i = 0;
        try {
            var builder = new Builder ();
            builder.add_from_file ("clickme-ext.glade");
            var window = builder.get_object ("window1") as Window;
            builder.connect_signals (builder);
            window.show_all ();
        } catch (Error e) {
            stderr.printf ("Could not load UI: %s\n", e.message);
            return 1;
        } 
        return 0;
    }
    public static int main (string[] args) {     
        Gtk.init (ref args);
        var h = new HelloWorld();
        h.run(args);
        Gtk.main ();
        return 0;
    }
}

Since class is isused, “clickme-ext.glade” is used here.

Although you see compiler warnings like “warning: method ... never used”, do not worry. They are used via Gtk.Builder callback mechanism.

Let’s compile gui-4.vala to create the ELF object gui-4 and run it.

$ valac -v --pkg gtk+-3.0 --pkg gmodule-2.0 gui-4.vala
gui-4.vala:7.5-7.41: warning: method `HelloWorld.on_button1_clicked' never used
    public static void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-4.vala:12.5-12.41: warning: method `HelloWorld.on_window1_destroy' never used...
    public static void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/path/to/vala-glade/gui-4.vala.c: In function ‘main’:
/path/to/vala-glade/gui-4.vala.c:167:2: warning: ‘g_type_init’ is deprecated (dec...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gmodule-2.0.vapi'
cc -o '/path/to/vala-glade/gui-4' '/path/to/vala-glade/gui-4.vala.c' -pthread -I/...
Compilation succeeded - 2 warning(s)

You can get the C source as:

$ valac -C --pkg gtk+-3.0 --pkg gmodule-2.0 gui-4.vala
gui-4.vala:7.5-7.41: warning: method `HelloWorld.on_button1_clicked' never used
    public static void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-4.vala:12.5-12.41: warning: method `HelloWorld.on_window1_destroy' never used...
    public static void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Compilation succeeded - 2 warning(s)
$ wc -l gui-4.vala ; wc -l gui-4.c
38 gui-4.vala
213 gui-4.c
$ cat gui-4.c |sed -e 's/       /    /g'|fold
/* gui-4.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-4.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>


#define TYPE_HELLO_WORLD (hello_world_get_type ())
#define HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_HELLO_WORLD, H
elloWorld))
#define HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_HELLO_W
ORLD, HelloWorldClass))
#define IS_HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_HELLO_WORLD
))
#define IS_HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_HELL
O_WORLD))
#define HELLO_WORLD_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_HELLO
_WORLD, HelloWorldClass))

typedef struct _HelloWorld HelloWorld;
typedef struct _HelloWorldClass HelloWorldClass;
typedef struct _HelloWorldPrivate HelloWorldPrivate;
#define _g_free0(var) (var = (g_free (var), NULL))
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_error_free0(var) ((var == NULL) ? NULL : (var = (g_error_free (var),
NULL)))

struct _HelloWorld {
    GObject parent_instance;
    HelloWorldPrivate * priv;
};

struct _HelloWorldClass {
    GObjectClass parent_class;
};


static gpointer hello_world_parent_class = NULL;
static gint hello_world_i;
static gint hello_world_i = 0;

GType hello_world_get_type (void) G_GNUC_CONST;
enum  {
    HELLO_WORLD_DUMMY_PROPERTY
};
void hello_world_on_button1_clicked (GtkButton* button);
void hello_world_on_window1_destroy (GtkWindow* window);
static gint hello_world_run (HelloWorld* self, gchar** args, int args_length1);
gint hello_world_main (gchar** args, int args_length1);
HelloWorld* hello_world_new (void);
HelloWorld* hello_world_construct (GType object_type);
static void hello_world_finalize (GObject* obj);


void hello_world_on_button1_clicked (GtkButton* button) {
    gint _tmp0_;
    GtkButton* _tmp1_;
    gint _tmp2_;
    gchar* _tmp3_ = NULL;
    gchar* _tmp4_;
    g_return_if_fail (button != NULL);
    _tmp0_ = hello_world_i;
    hello_world_i = _tmp0_ + 1;
    _tmp1_ = button;
    _tmp2_ = hello_world_i;
    _tmp3_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp2_);
    _tmp4_ = _tmp3_;
    gtk_button_set_label (_tmp1_, _tmp4_);
    _g_free0 (_tmp4_);
}


void hello_world_on_window1_destroy (GtkWindow* window) {
    g_return_if_fail (window != NULL);
    gtk_main_quit ();
}


static gpointer _g_object_ref0 (gpointer self) {
    return self ? g_object_ref (self) : NULL;
}


static gint hello_world_run (HelloWorld* self, gchar** args, int args_length1) {
    gint result = 0;
    GError * _inner_error_ = NULL;
    g_return_val_if_fail (self != NULL, 0);
    hello_world_i = 0;
    {
        GtkBuilder* _tmp0_;
        GtkBuilder* builder;
        GtkBuilder* _tmp1_;
        GtkBuilder* _tmp2_;
        GObject* _tmp3_ = NULL;
        GtkWindow* _tmp4_;
        GtkWindow* window;
        GtkBuilder* _tmp5_;
        GtkBuilder* _tmp6_;
        GtkWindow* _tmp7_;
        _tmp0_ = gtk_builder_new ();
        builder = _tmp0_;
        _tmp1_ = builder;
        gtk_builder_add_from_file (_tmp1_, "clickme-ext.glade", &_inner_error_);
        if (_inner_error_ != NULL) {
            _g_object_unref0 (builder);
            goto __catch0_g_error;
        }
        _tmp2_ = builder;
        _tmp3_ = gtk_builder_get_object (_tmp2_, "window1");
        _tmp4_ = _g_object_ref0 (G_TYPE_CHECK_INSTANCE_TYPE (_tmp3_, GTK_TYPE_WI
NDOW) ? ((GtkWindow*) _tmp3_) : NULL);
        window = _tmp4_;
        _tmp5_ = builder;
        _tmp6_ = builder;
        gtk_builder_connect_signals (_tmp5_, _tmp6_);
        _tmp7_ = window;
        gtk_widget_show_all ((GtkWidget*) _tmp7_);
        _g_object_unref0 (window);
        _g_object_unref0 (builder);
    }
    goto __finally0;
    __catch0_g_error:
    {
        GError* e = NULL;
        FILE* _tmp8_;
        GError* _tmp9_;
        const gchar* _tmp10_;
        e = _inner_error_;
        _inner_error_ = NULL;
        _tmp8_ = stderr;
        _tmp9_ = e;
        _tmp10_ = _tmp9_->message;
        fprintf (_tmp8_, "Could not load UI: %s\n", _tmp10_);
        result = 1;
        _g_error_free0 (e);
        return result;
    }
    __finally0:
    if (_inner_error_ != NULL) {
        g_critical ("file %s: line %d: uncaught error: %s (%s, %d)", __FILE__, _
_LINE__, _inner_error_->message, g_quark_to_string (_inner_error_->domain), _inn
er_error_->code);
        g_clear_error (&_inner_error_);
        return 0;
    }
    result = 0;
    return result;
}


gint hello_world_main (gchar** args, int args_length1) {
    gint result = 0;
    HelloWorld* _tmp0_;
    HelloWorld* h;
    gchar** _tmp1_;
    gint _tmp1__length1;
    gtk_init (&args_length1, &args);
    _tmp0_ = hello_world_new ();
    h = _tmp0_;
    _tmp1_ = args;
    _tmp1__length1 = args_length1;
    hello_world_run (h, _tmp1_, _tmp1__length1);
    gtk_main ();
    result = 0;
    _g_object_unref0 (h);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return hello_world_main (argv, argc);
}


HelloWorld* hello_world_construct (GType object_type) {
    HelloWorld * self = NULL;
    self = (HelloWorld*) g_object_new (object_type, NULL);
    return self;
}


HelloWorld* hello_world_new (void) {
    return hello_world_construct (TYPE_HELLO_WORLD);
}


static void hello_world_class_init (HelloWorldClass * klass) {
    hello_world_parent_class = g_type_class_peek_parent (klass);
    G_OBJECT_CLASS (klass)->finalize = hello_world_finalize;
}


static void hello_world_instance_init (HelloWorld * self) {
}


static void hello_world_finalize (GObject* obj) {
    HelloWorld * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_HELLO_WORLD, HelloWorld);
    G_OBJECT_CLASS (hello_world_parent_class)->finalize (obj);
}


GType hello_world_get_type (void) {
    static volatile gsize hello_world_type_id__volatile = 0;
    if (g_once_init_enter (&hello_world_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (HelloWorldClass),
(GBaseInitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) hello_world_cla
ss_init, (GClassFinalizeFunc) NULL, NULL, sizeof (HelloWorld), 0, (GInstanceInit
Func) hello_world_instance_init, NULL };
        GType hello_world_type_id;
        hello_world_type_id = g_type_register_static (G_TYPE_OBJECT, "HelloWorld
", &g_define_type_info, 0);
        g_once_init_leave (&hello_world_type_id__volatile, hello_world_type_id);
    }
    return hello_world_type_id__volatile;
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI

OOP style (main inside of class, callback as instance)

Source code gui-5.vala in Vala language

using Gtk;

class HelloWorld : Object {

    private int i;

    [CCode (instance_pos = -1)]
    public void on_button1_clicked (Button button) {
        this.i += 1;
        button.label = "Hello, World!\nClick count = %i".printf(this.i);
    }

    [CCode (instance_pos = -1)]
    public void on_window1_destroy (Window window) {
        Gtk.main_quit ();
    }

    private int run (string[] args) {     
        this.i = 0;
        try {
            var builder = new Builder ();
            builder.add_from_file ("clickme-ext.glade");
            var window = builder.get_object ("window1") as Window;
            builder.connect_signals (builder);
            window.show_all ();
        } catch (Error e) {
            stderr.printf ("Could not load UI: %s\n", e.message);
            return 1;
        } 
        return 0;
    }
    public static int main (string[] args) {     
        Gtk.init (ref args);
        var h = new HelloWorld();
        h.run(args);
        Gtk.main ();
        return 0;
    }
}

Since class is isused, “clickme-ext.glade” is used here.

Although you see compiler warnings like “warning: method ... never used”, do not worry. They are used via Gtk.Builder callback mechanism.

Please make sure to use “[CCode (instance_pos = -1)]” when using instance methods instead of static methods as callback handlers for the Gtk.Builder’s signal auto-connection mechanism.

Let’s compile gui-5.vala to create the ELF object gui-5 and run it.

$ valac -v --pkg gtk+-3.0 --pkg gmodule-2.0 gui-5.vala
gui-5.vala:8.5-8.34: warning: method `HelloWorld.on_button1_clicked' never used
    public void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-5.vala:14.5-14.34: warning: method `HelloWorld.on_window1_destroy' never used...
    public void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/path/to/vala-glade/gui-5.vala.c: In function ‘main’:
/path/to/vala-glade/gui-5.vala.c:172:2: warning: ‘g_type_init’ is deprecated (dec...
  g_type_init ();
  ^
Loaded package `/usr/share/vala-0.20/vapi/glib-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gobject-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gtk+-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gio-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/atk.vapi'
Loaded package `/usr/share/vala-0.20/vapi/cairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-pixbuf-2.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gdk-3.0.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pango.vapi'
Loaded package `/usr/share/vala-0.20/vapi/pangocairo.vapi'
Loaded package `/usr/share/vala-0.20/vapi/x11.vapi'
Loaded package `/usr/share/vala-0.20/vapi/gmodule-2.0.vapi'
cc -o '/path/to/vala-glade/gui-5' '/path/to/vala-glade/gui-5.vala.c' -pthread -I/...
Compilation succeeded - 2 warning(s)

You can get the C source as:

$ valac -C --pkg gtk+-3.0 --pkg gmodule-2.0 gui-5.vala
gui-5.vala:8.5-8.34: warning: method `HelloWorld.on_button1_clicked' never used
    public void on_button1_clicked (Button button) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gui-5.vala:14.5-14.34: warning: method `HelloWorld.on_window1_destroy' never used...
    public void on_window1_destroy (Window window) {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Compilation succeeded - 2 warning(s)
$ wc -l gui-5.vala ; wc -l gui-5.c
40 gui-5.vala
220 gui-5.c
$ cat gui-5.c |sed -e 's/       /    /g'|fold
/* gui-5.c generated by valac 0.20.1, the Vala compiler
 * generated from gui-5.vala, do not modify */


#include <glib.h>
#include <glib-object.h>
#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>


#define TYPE_HELLO_WORLD (hello_world_get_type ())
#define HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), TYPE_HELLO_WORLD, H
elloWorld))
#define HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), TYPE_HELLO_W
ORLD, HelloWorldClass))
#define IS_HELLO_WORLD(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), TYPE_HELLO_WORLD
))
#define IS_HELLO_WORLD_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TYPE_HELL
O_WORLD))
#define HELLO_WORLD_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), TYPE_HELLO
_WORLD, HelloWorldClass))

typedef struct _HelloWorld HelloWorld;
typedef struct _HelloWorldClass HelloWorldClass;
typedef struct _HelloWorldPrivate HelloWorldPrivate;
#define _g_free0(var) (var = (g_free (var), NULL))
#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (va
r), NULL)))
#define _g_error_free0(var) ((var == NULL) ? NULL : (var = (g_error_free (var),
NULL)))

struct _HelloWorld {
    GObject parent_instance;
    HelloWorldPrivate * priv;
};

struct _HelloWorldClass {
    GObjectClass parent_class;
};

struct _HelloWorldPrivate {
    gint i;
};


static gpointer hello_world_parent_class = NULL;

GType hello_world_get_type (void) G_GNUC_CONST;
#define HELLO_WORLD_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), TYPE_HELLO
_WORLD, HelloWorldPrivate))
enum  {
    HELLO_WORLD_DUMMY_PROPERTY
};
void hello_world_on_button1_clicked (GtkButton* button, HelloWorld* self);
void hello_world_on_window1_destroy (GtkWindow* window, HelloWorld* self);
static gint hello_world_run (HelloWorld* self, gchar** args, int args_length1);
gint hello_world_main (gchar** args, int args_length1);
HelloWorld* hello_world_new (void);
HelloWorld* hello_world_construct (GType object_type);
static void hello_world_finalize (GObject* obj);


void hello_world_on_button1_clicked (GtkButton* button, HelloWorld* self) {
    gint _tmp0_;
    GtkButton* _tmp1_;
    gint _tmp2_;
    gchar* _tmp3_ = NULL;
    gchar* _tmp4_;
    g_return_if_fail (self != NULL);
    g_return_if_fail (button != NULL);
    _tmp0_ = self->priv->i;
    self->priv->i = _tmp0_ + 1;
    _tmp1_ = button;
    _tmp2_ = self->priv->i;
    _tmp3_ = g_strdup_printf ("Hello, World!\nClick count = %i", _tmp2_);
    _tmp4_ = _tmp3_;
    gtk_button_set_label (_tmp1_, _tmp4_);
    _g_free0 (_tmp4_);
}


void hello_world_on_window1_destroy (GtkWindow* window, HelloWorld* self) {
    g_return_if_fail (self != NULL);
    g_return_if_fail (window != NULL);
    gtk_main_quit ();
}


static gpointer _g_object_ref0 (gpointer self) {
    return self ? g_object_ref (self) : NULL;
}


static gint hello_world_run (HelloWorld* self, gchar** args, int args_length1) {
    gint result = 0;
    GError * _inner_error_ = NULL;
    g_return_val_if_fail (self != NULL, 0);
    self->priv->i = 0;
    {
        GtkBuilder* _tmp0_;
        GtkBuilder* builder;
        GtkBuilder* _tmp1_;
        GtkBuilder* _tmp2_;
        GObject* _tmp3_ = NULL;
        GtkWindow* _tmp4_;
        GtkWindow* window;
        GtkBuilder* _tmp5_;
        GtkBuilder* _tmp6_;
        GtkWindow* _tmp7_;
        _tmp0_ = gtk_builder_new ();
        builder = _tmp0_;
        _tmp1_ = builder;
        gtk_builder_add_from_file (_tmp1_, "clickme-ext.glade", &_inner_error_);
        if (_inner_error_ != NULL) {
            _g_object_unref0 (builder);
            goto __catch0_g_error;
        }
        _tmp2_ = builder;
        _tmp3_ = gtk_builder_get_object (_tmp2_, "window1");
        _tmp4_ = _g_object_ref0 (G_TYPE_CHECK_INSTANCE_TYPE (_tmp3_, GTK_TYPE_WI
NDOW) ? ((GtkWindow*) _tmp3_) : NULL);
        window = _tmp4_;
        _tmp5_ = builder;
        _tmp6_ = builder;
        gtk_builder_connect_signals (_tmp5_, _tmp6_);
        _tmp7_ = window;
        gtk_widget_show_all ((GtkWidget*) _tmp7_);
        _g_object_unref0 (window);
        _g_object_unref0 (builder);
    }
    goto __finally0;
    __catch0_g_error:
    {
        GError* e = NULL;
        FILE* _tmp8_;
        GError* _tmp9_;
        const gchar* _tmp10_;
        e = _inner_error_;
        _inner_error_ = NULL;
        _tmp8_ = stderr;
        _tmp9_ = e;
        _tmp10_ = _tmp9_->message;
        fprintf (_tmp8_, "Could not load UI: %s\n", _tmp10_);
        result = 1;
        _g_error_free0 (e);
        return result;
    }
    __finally0:
    if (_inner_error_ != NULL) {
        g_critical ("file %s: line %d: uncaught error: %s (%s, %d)", __FILE__, _
_LINE__, _inner_error_->message, g_quark_to_string (_inner_error_->domain), _inn
er_error_->code);
        g_clear_error (&_inner_error_);
        return 0;
    }
    result = 0;
    return result;
}


gint hello_world_main (gchar** args, int args_length1) {
    gint result = 0;
    HelloWorld* _tmp0_;
    HelloWorld* h;
    gchar** _tmp1_;
    gint _tmp1__length1;
    gtk_init (&args_length1, &args);
    _tmp0_ = hello_world_new ();
    h = _tmp0_;
    _tmp1_ = args;
    _tmp1__length1 = args_length1;
    hello_world_run (h, _tmp1_, _tmp1__length1);
    gtk_main ();
    result = 0;
    _g_object_unref0 (h);
    return result;
}


int main (int argc, char ** argv) {
    g_type_init ();
    return hello_world_main (argv, argc);
}


HelloWorld* hello_world_construct (GType object_type) {
    HelloWorld * self = NULL;
    self = (HelloWorld*) g_object_new (object_type, NULL);
    return self;
}


HelloWorld* hello_world_new (void) {
    return hello_world_construct (TYPE_HELLO_WORLD);
}


static void hello_world_class_init (HelloWorldClass * klass) {
    hello_world_parent_class = g_type_class_peek_parent (klass);
    g_type_class_add_private (klass, sizeof (HelloWorldPrivate));
    G_OBJECT_CLASS (klass)->finalize = hello_world_finalize;
}


static void hello_world_instance_init (HelloWorld * self) {
    self->priv = HELLO_WORLD_GET_PRIVATE (self);
}


static void hello_world_finalize (GObject* obj) {
    HelloWorld * self;
    self = G_TYPE_CHECK_INSTANCE_CAST (obj, TYPE_HELLO_WORLD, HelloWorld);
    G_OBJECT_CLASS (hello_world_parent_class)->finalize (obj);
}


GType hello_world_get_type (void) {
    static volatile gsize hello_world_type_id__volatile = 0;
    if (g_once_init_enter (&hello_world_type_id__volatile)) {
        static const GTypeInfo g_define_type_info = { sizeof (HelloWorldClass),
(GBaseInitFunc) NULL, (GBaseFinalizeFunc) NULL, (GClassInitFunc) hello_world_cla
ss_init, (GClassFinalizeFunc) NULL, NULL, sizeof (HelloWorld), 0, (GInstanceInit
Func) hello_world_instance_init, NULL };
        GType hello_world_type_id;
        hello_world_type_id = g_type_register_static (G_TYPE_OBJECT, "HelloWorld
", &g_define_type_info, 0);
        g_once_init_leave (&hello_world_type_id__volatile, hello_world_type_id);
    }
    return hello_world_type_id__volatile;
}

It is obvious that the Vala code is much shorter than the generated C code. The Vala compiler took care chores of generating CPP macros for GObject with.

• No prefix.
• gui, GUI, Gui: object type (= class) name
• gui_get_type(): returning GType of object GUI