private void CommandExecuted(object sender, ExecutedRoutedEventArgs e)
        {
            // Ignore menu button source.
            if (e.Source is ICommandSource) return;

            // Ignore the ApplicationUndo command.
            if (e.Command == MonitorCommands.ApplicationUndo) return;

            // Could filter for commands you want to add to the stack
            // (for example, not selection events).

            TextBox txt = e.Source as TextBox;
            if (txt != null)
            {
                RoutedCommand cmd = (RoutedCommand)e.Command;
                
                CommandHistoryItem historyItem = new CommandHistoryItem(
                    cmd.Name, txt, "Text", txt.Text);

                ListBoxItem item = new ListBoxItem();
                item.Content = historyItem;
                lstHistory.Items.Add(historyItem);

               // CommandManager.InvalidateRequerySuggested();
            }
        }