private void CommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
//当触发CommandManager.PreviewExecuted事件时，需要确定准备执行的命令是否是我们所关心的，如果是，可创建CommandHistoryItem对象，并将
//其添加到Undo堆栈中
//注意两个潜在问题：
//1.当单击工具栏按钮以在文本框上执行命令时，CommandManager.PreviewExecuted事件被引发了两次——一次是针对工具栏按钮，另一次是针对文本框
//下面的代码通过忽略发送者是ICommandSource的命令，避免在Undo历史中重复条目
//2.需要明确忽略不希望添加到Undo历史中的命令
//例如ApplicationUndo命令，通过该命令可翻转上一步操作
// 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);
//本例在ListBox控件中存储所有CommandHistoryItem对象。ListBox控件的DisplayMember属性被设置为Name，因而会显示每个条目的CommandHistoryItem.Name属性
//CommandManager.InvalidateRequerySuggested();
}
}