net无限级分类

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class ex : System.Web.UI.Page
{
     public DataTable ds = new DataTable();
     protected void Page_Load(object sender, EventArgs e)
     {
         int parentid;
         if (Request["parentid"] == "")
         {
             parentid = 0;
         }
         else
         {
             parentid =Convert.ToInt32(Request["parentid"]);
         }
         databind();
        treebind(0);
        
     
     }
     public void databind()
     {
         SqlConnection myconn = db.openconn();
         if (myconn.State == ConnectionState.Closed)
         {
             myconn.Open();
         }
         string sql = "select * from aclass";
         SqlDataAdapter sda = new SqlDataAdapter(sql, myconn);
         sda.Fill(ds);

     }
     public void treebind(int pd)
     {
         string parentid = "parent_id=" + pd;
         DataRow[] dr = ds.Select(parentid);
         //Response.Write(dr.Length);
    
         for (int i = 0; i < dr.Length; i++)
         {
             if (Convert.ToInt32(dr[i][1]) == pd)
             {
                 string cname =dr[i][2].ToString();
                 int j = Convert.ToInt32(dr[i][0]);
                 Response.Write("<ul><li><a href='ex.aspx?id="+dr[i][0]+"&parentid="+dr[i][1]+"'>"+cname+"</a>");
            
                 treebind(j);
                 Response.Write("</li></ul>");
             }
         }
       
     }
}