我们在数据库中 存的是

id   name ParentID(父节点)

1    新闻    0

2      国内    1

3    山东     2

………………

显示为：

public void GetAllArticleClass()
        {
          
            string sqlStr = "select * from ArticleClass where ParentID=0";//显示最顶层所有

            foreach (DataRow dr in con.conDataSet(sqlStr, "0").Tables[0].Rows)//加顶层
            {
                dropAddPurview.Items.Add(new ListItem(dr["ClassName"].ToString(), dr["ClassID"].ToString()));
                num = 0;
                this.ab(dr["ClassID"].ToString());//调用递归！
             }                
         }
        private void ab(string id)//递归
        {
          
            string sqlStr = "select * from ArticleClass where ParentID="+id+"";

            foreach (DataRow dr in con.conDataSet(sqlStr, "0").Tables[0].Rows)//
            {
                dropAddPurview.Items.Add(new ListItem(this.stradd(int.Parse(dr["Depth"].ToString())) + dr["ClassName"].ToString(), dr["ClassID"].ToString()));
                // if (id != dr["ParentID"].ToString())
                ab(dr["ClassID"].ToString());

            }

        }
private string stradd(int num)//级别链接字符
        {
            string str = "";

            for (int i = 0; i < num; i++)
            {

                if (num == 1 || num - i == 1)

                    str += "┕┅ ";
                else

                str += Server.HtmlDecode("        ");//因为droplist 不直接支持html标记，所以我们采用 服务器对空格解码！
            
            }
            return str;
        }