simple widget example

foo-widget.c

#include "foo-widget.h"

struct _FooWidget
{
  GtkBin parent_instance;
  GtkLabel *label;
};

G_DEFINE_TYPE (FooWidget, foo_widget, GTK_TYPE_BIN)

static void
foo_widget_class_init (FooWidgetClass *klass)
{
  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);

  gtk_widget_class_set_css_name (widget_class, "foowidget");
  gtk_widget_class_set_template_from_resource (widget_class, "/foo/widget.ui");
  gtk_widget_class_bind_template_child (widget_class, FooWidget, label);
}

static void
foo_widget_init (FooWidget *self)
{
  gtk_widget_init_template (GTK_WIDGET (self));
}

GtkWidget *
foo_widget_new (void)
{
  return g_object_new (FOO_TYPE_WIDGET, NULL);
}

foo-widget.h

#ifndef FOO_WIDGET_H
#define FOO_WIDGET_H

#include <gtk/gtk.h>

G_BEGIN_DECLS

#define FOO_TYPE_WIDGET (foo_widget_get_type())

G_DECLARE_FINAL_TYPE (FooWidget, foo_widget, FOO, WIDGET, GtkBin)

GtkWidget *foo_widget_new (void);

G_END_DECLS

#endif /* FOO_WIDGET_H */

foo-widget.ui

<?xml version="1.0" encoding="utf-8"?>
<interface>
  <template class="FooWidget" parent="GtkBin">
   <child>
    <object class="GtkLabel" id="label">
     <property name="label">Hello, World!</property>
     <property name="visible">true</property>
    </object>
   </child>
  </template>
</interface>