Vista - handling command in menuitem

hi all, I set command to menuitem and I add command binding to rootpage
to enable command. It doesn't work. If I add command binding to
menuitem it works. the code as following:

XMAL :
<MenuItem x:Name="XMenuItem" Header="MenuItem" Command
="Open"/>

In Code Behind:

public partial class MenuToolBarTestCase : Page
{
public MenuToolBarTestCase()
{
InitializeComponent();
Loaded += new
RoutedEventHandler(MenuToolBarTestCase_Loaded);
}
void MenuToolBarTestCase_Loaded(object sender, RoutedEventArgs
e)
{
CommandBinding CB = new CommandBinding(XMenuItem.Command);
CB.CanExecute += new
CanExecuteRoutedEventHandler(CB_CanExecute);
CB.Executed += new ExecutedRoutedEventHandler(CB_Executed);
//It doesn't work
this.CommandBindings.Add(CB);
// If I change the code as following it works
XMenuItem.CommandBindings.Add(CB);
}
}

If command is assigned to control (e.g. button and menuitem). It can't
be enable by parent or other controls via commandbinding?


Virtual