添加右键上下文菜单后，点击后需要获取到源控件
private void MenuItem_Click(object sender, RoutedEventArgs e)
{
if (sender is MenuItem item &&
item.Parent is ContextMenu menu && //获取ContextMenu
menu.PlacementTarget is ListBoxItem listitem && //获取到关联的控件
listitem.DataContext is string str)
{
//复制
Clipboard.SetDataObject(str);
}
}
