猜猜这个的输出结果是什么

Question

TreeView tv = new TreeView();
                User info = new User();
                info.UserID = "ABC";
                info.UserName = "DEF";
                TreeNode node = new TreeNode(info.UserID);
                node.Tag = info;
                tv.Nodes.Add(node);                ListView lv = new ListView();
                ListViewItem lvItem = new ListViewItem(info.UserID);
                lvItem.Tag = info;
                lv.Items.Add(lvItem);                Console.WriteLine(((User)tv.Nodes[0].Tag).ToString());                Console.WriteLine(((User)lv.Items[0].Tag).ToString());                ((User)tv.Nodes[0].Tag).UserID = "HAHAHAAHA";                tv.Nodes[0].Tag = null;                Console.WriteLine(((User)tv.Nodes[0].Tag).ToString());                Console.WriteLine(((User)lv.Items[0].Tag).ToString());class User
    {
        public User(string id, string name)
        {
            UserID = id;
            UserName = name;
        }        public User()
        {
        }        public string UserID = string.Empty;        public string UserName = string.Empty;        public override string ToString()
        {
            return string.Format("UserID:{0},UserName", UserID, UserName);
        }
    }猜猜这个的输出结果是什么？

Answer 1

如果你代码没有输入手误的话我认为应该是：
//UserID:ABC,UserName
//UserID:ABC,UserName
//报告nullreferenceexception错误
//UserID:HAHAHAAHA,UserName(但因上句报错而不会被执行。)