makefile
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ALL:
    valac-0.14 --pkg gtk+-3.0 --pkg gmodule-2.0 simplecase.vala -o simplecase
    valac-0.14 --pkg gtk+-3.0 --pkg gmodule-2.0 simplecase.vala --ccode

simplecase.vala
---------------------------------------------------------------------
using Gtk;

namespace Foo {
    public class Bar : Object {
        private bool try_me;
        public Bar( ) {
            this.try_me = false;

            try {
                var builder = new Builder( );
                builder.add_from_file( "test.glade" );
                builder.connect_signals( this );
                var window = builder.get_object( "window1" ) as Window;
                window.show_all( );
            } catch( Error e ) {
                stdout.printf( "%s\n", e.message );
            }
        }

        [CCode( instance_pos=-1 )]
        public void click_cb( Button btn ) {
            stdout.printf( "clicked\n" );

            stdout.printf( "val: %s\n", this.try_me.to_string( ) );
            GLib.error ("%p", this);
        }

        public static void main( string[] args ) {
            Gtk.init( ref args );
            new Bar( );
            Gtk.main( );
        }
    }
}


test.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>
    <signal name="destroy" handler="gtk_main_quit" swapped="no"/>
    <child>
      <object class="GtkBox" id="box1">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="orientation">vertical</property>
        <child>
          <object class="GtkButton" id="button1">
            <property name="label" translatable="yes">button</property>
            <property name="use_action_appearance">False</property>
            <property name="visible">True</property>
            <property name="can_focus">True</property>
            <property name="receives_default">True</property>
            <property name="use_action_appearance">False</property>
            <signal name="clicked" handler="foo_bar_click_cb" swapped="no"/>
          </object>
          <packing>
            <property name="expand">False</property>
            <property name="fill">True</property>
            <property name="position">0</property>
          </packing>
        </child>
      </object>
    </child>
  </object>
</interface>