省市县三级连动（数据在一个表中）

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="省市县三级连接.aspx.cs" Inherits="省级连动.省市县三级连接" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

前台：

后台：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;

namespace 省级连动
{
    public partial class 省市县三级连接 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                GetProvince();
            }
        }

        private void LoadData(string id, DropDownList ddl)
        {
            string strcon = "Data Source=PC-Dll;Initial Catalog=News; Persist Security Info=true;User Id=sa;Password=linlin ";
            SqlConnection conn = new SqlConnection(strcon);
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = "SELECT A_Id,A_Name FROM T_Arear WHERE A_ParentId=@parentid ORDER BY A_Id";
            cmd.Parameters.AddWithValue("@parentid",id);
            SqlDataAdapter adapter = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            adapter.Fill(dt);
            cmd.Dispose();
            conn.Dispose();

            ddl.DataSource = dt;
            ddl.DataTextField = "A_Name";
            ddl.DataValueField = "A_Id";
            ddl.DataBind();
            if (id=="0")
            {
                ListItem item = new ListItem("-------请选择-------","0");
                ddl.Items.Insert(0,item);
            }
        }

        private void GetProvince()
        {
            LoadData("0",this.ddlProvince);
        }

        protected void ddlProvince_SelectedIndexChanged(object sender, EventArgs e)
        {
            string id = this.ddlProvince.SelectedItem.Value;
            if (id != "0")
            {
                LoadData(id, this.ddlCity);
                string selectid = this.ddlCity.SelectedItem.Value;
                LoadData(selectid, this.ddlArear);
            }
            else
            {
                this.ddlCity.Items.Clear();
                this.ddlArear.Items.Clear();
            }
        }

        protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
        {
            string id = this.ddlCity.SelectedItem.Value;
            LoadData(id,this.ddlArear);
        }
    }
}