interface.xml

<interface>
  <object class="GtkUIManager" id="uiman">
    <child>
      <object class="GtkActionGroup" id="actiongroup">
        <child>
          <object class="GtkAction" id="file">
            <property name="label">_File</property>
          </object>
        </child>
      </object>
    </child>
    <ui>
      <menubar name="menubar1">
        <menu action="file"/>
      </menubar>
    </ui>
  </object>
  <object class="GtkWindow" id="main_window">
    <property name="type">GTK_WINDOW_TOPLEVEL</property>
    <property name="title">astrid</property>
    <property name="default_width">800</property> 
    <property name="default_height">600</property>
    <property name="border-width">20</property>
    <signal name="delete-event" handler="on_destroy"/>
    <signal name="destroy" handler="on_destroy"/>
    <child> 
      <object class="GtkVBox" id="vbox1"> 
        <property name="visible">TRUE</property> 
        <child>
          <object class="GtkMenuBar" id="menubar1" constructor="uiman"/>
          <packing> 
            <property name="expand">FALSE</property> 
          </packing> 
        </child>
    </child>
  </object>
</interface>