droplist下拉层级选择

 public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindDrpClass();
            }
        }
        private void BindDrpClass()
        {
            //获得所有数据列表
            Maticsoft.BLL.L_Men sm = new Maticsoft.BLL.L_Men();
            DataSet ds;
            ds = sm.GetList("");
            DataTable dt = ds.Tables[0];
            ddl.Items.Clear();
            ddl.Items.Add(new ListItem("选择类别", "0"));
            DataRow[] drs = dt.Select("MenParentID= " + 0);//得到父ID

            foreach (DataRow dr in drs)
            {
                string classid = dr["MenID"].ToString();
                string classname = dr["MenName"].ToString();
                //顶级分类显示形式
                classname = "" + classname;

                ddl.Items.Add(new ListItem(classname, classid));
                int sonparentid = int.Parse(classid);
                string blank = "　|---";
                //递归子分类方法
                BindNode(sonparentid, dt, blank);
            }
            ddl.DataBind();
        }
        private void BindNode(int parentid, DataTable dt, string blank)
        {
            DataRow[] drs = dt.Select("MenParentID= " + parentid);

            foreach (DataRow dr in drs)
            {
                string classid = dr["MenID"].ToString();
                string classname = dr["MenName"].ToString();

                classname = blank + classname;
                ddl.Items.Add(new ListItem(classname, classid));

                int sonparentid = int.Parse(classid);
                string blank2 = blank + "-";
                BindNode(sonparentid, dt, blank2);
            }
        }

        protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
        {
            Response.Write("选择值是:"+ddl.SelectedValue);
        }

        protected void Button1_Click(object sender, EventArgs e)
        {

        }
      
    }