asp.net无刷新三级联动

无刷新三级联动，这个在网上有很多，方法也很好。但是有一点比较特别的就是我的这个，是因为单位已经建立好了数据库，你得在这个上面进行添加。所以很麻烦啊。在网上也找了一些，可是大多数数据库都不一样，有一些是用vs2005和ajaxpro做的，可是我单位使用的是vs2003没有法子，只能找一些可以用了。这里要感谢的是 Eric 它在baidu的BLOG里的方法不错，我基本是采用它的方法来做的，只不过这里做了一些改动。
     首先是。ThreeDDL.aspx页面,我把程序全写上来，
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>无标题页</title>

         <script language="javascript">
     <!--
      function SelectProvince()
      {
         var drp2=document.getElementById("DropDownList2");//市县一级
         var drp3=document.getElementById("DropDownList3");//区一级
         for (var i=drp2.options.length;i>=0;i--)
         {
             drp2.remove(i);
         }
         for (var i=drp3.options.length;i>=0;i--)
         {
             drp3.remove(i);
         }
         var oHttpReq=new ActiveXObject("MSXML2.XMLHTTP");
         var oDoc=new ActiveXObject("MSXML2.DOMDocument");
         var province=document.getElementById("DropDownList1").value;
         oHttpReq.open("post","selectarea.aspx?flag=1&province="+province,false);
         oHttpReq.setrequestheader("content-type","application/x-www-form-urlencoded");
         oHttpReq.send("");
         var result=oHttpReq.responseText;
         var newOption_0 = document.createElement("OPTION");
         newOption_0.text = "-请选择-";
         newOption_0.value = '-1';
         drp2.options.add(newOption_0);
         oDoc.loadXML(result);
        //这里要说一下，items1和items2是你在后面程序中得到的一个xml表。对于//NewDataSet/city/name是怎么来的，你可以用alert(result);看一下就行
    items1 = oDoc.selectNodes("//NewDataSet/city/name");
        items2 = oDoc.selectNodes("//NewDataSet/city/sz_code");

var itemsLength=items1.length;

for(i=0;i<itemsLength;i++)

//将小类的类名和编号赋予DropDownList2
    {
    var newOption = document.createElement("OPTION");
    newOption.text=items1[i].text;
    newOption.value=items2[i].text;
    drp2.options.add(newOption);
    }
    }


     function SelectCity()
      {
         var drp3=document.getElementById("DropDownList3");
         for (var i=drp3.options.length;i>=0;i--)
         {
             drp3.remove(i);
         }

         var oHttpReq=new ActiveXObject("MSXML2.XMLHTTP");
         var oDoc=new ActiveXObject("MSXML2.DOMDocument");
         var city=document.getElementById("DropDownList2").value;
         oHttpReq.open("post","selectarea.aspx?flag=2&city="+city,false);
         oHttpReq.setrequestheader("content-type","application/x-www-form-urlencoded");
         oHttpReq.send("");
         var result=oHttpReq.responseText;
         var newOption_0 = document.createElement("OPTION");
         newOption_0.text = "-请选择-";
         newOption_0.value = '-1';
         drp3.options.add(newOption_0);
         oDoc.loadXML(result);
         var items = oDoc.selectNodes("//NewDataSet/area");
    for (var item = items.nextNode();item;item = items.nextNode())
    {　
    　
    　var areaName = item.selectSingleNode("name").nodeTypedValue;
    　var areaCode = item.selectSingleNode("sz_code").nodeTypedValue;
      var newOption = document.createElement("OPTION");　
    　newOption.text = areaName;　
    　newOption.value = areaCode;　
    　drp3.options.add(newOption);　
    }　
    }


-->
     </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="DropDownList1" runat="server">
        </asp:DropDownList>
        <asp:DropDownList ID="DropDownList2" runat="server">
        </asp:DropDownList>
        <asp:DropDownList ID="DropDownList3" runat="server">
        </asp:DropDownList></div>
    </form>
</body>
</html>
下面是ThreeDDl.aspx.cs的代码
protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection conn = new SqlConnection("Data Source=CG;Initial Catalog=area;User ID=sa;Password=chen123");

SqlDataAdapter da = new SqlDataAdapter("select * from area where right(sz_code,4)='0000'",conn);
DataSet ds = new DataSet();

        da.Fill(ds, "Province");
        this.DropDownList1.DataSource = ds.Tables["Province"];
        this.DropDownList1.DataTextField = "name";
        this.DropDownList1.DataValueField = "sz_code";
        this.DropDownList1.DataBind();

        this.DropDownList1.Attributes.Add("onchange", "SelectProvince()");
        this.DropDownList2.Attributes.Add("onchange", "SelectCity()");
    }

selectarea.aspx这个页面上面没有什么东西，只有在其selectarea.aspx.cs中才有代码，在下面
using System;
using System.Data;
using System.Data.SqlClient;
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.Xml;

public partial class selectarea : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection conn = new SqlConnection("Data Source=CG;Initial Catalog=area;User ID=sa;Password=chen123");
        int flag = Convert.ToInt32(Request.QueryString["flag"].ToString());
        if (Request.QueryString["flag"] != null || Request.QueryString["flag"].ToString() != "")
        {
            switch(flag)
            {
                case 1:

                    string strprv = Request.QueryString["province"].ToString();
                    SqlDataAdapter da = new SqlDataAdapter("select * from area where left(sz_code,2)='" + strprv.Substring(0, 2).ToString() + "' and right(sz_code,2)='00' and right(sz_code,4)<>'0000'", conn);
                    DataSet ds = new DataSet();

                    da.Fill(ds,"city");
                    XmlTextWriter writerCity = new XmlTextWriter(Response.OutputStream, Response.ContentEncoding);
                    writerCity.Formatting = Formatting.Indented;
                    writerCity.Indentation = 4;
                    writerCity.IndentChar = ' ';
                    ds.WriteXml(writerCity);
                    writerCity.Flush();
                    Response.End();
                    writerCity.Close();
                    break;
                case 2:
                    string strcity = Request.QueryString["city"].ToString();
                    SqlDataAdapter da1 = new SqlDataAdapter("select * from area where left(sz_code,4)='" + strcity.Substring(0, 4).ToString() + "' and right(sz_code,2)<>'00'", conn);
                    DataSet ds1 = new DataSet();

                    da1.Fill(ds1, "area");
                    XmlTextWriter writerCity1 = new XmlTextWriter(Response.OutputStream, Response.ContentEncoding);
                    writerCity1.Formatting = Formatting.Indented;
                    writerCity1.Indentation = 4;
                    writerCity1.IndentChar = ' ';
                    ds1.WriteXml(writerCity1);
                    writerCity1.Flush();
                    Response.End();
                    writerCity1.Close();
                    break;
           }
        }
    }
}

这里我把数据库的大概情况给大家发一下，如果想要数据库ftp://down:down@ftp.netc.hutc.zj.cn/city.rar这个是Eric朋友提供的下载我不知道能用多长时间，我单位的数据库与它差不多，因为我无法提供我的数据库，所以以上代码全是根据它的数据库格式写的。
表名area
id name Rome sz_code zm_code
1 北京 Beijing Shi 110000 BJ

这里说一下，省一级的包括北京，天津这样的独立的市，sz_code全是前二位有数，后四位全是0000
而下面一级的，市县一级的则是前二位与省级一样，中间二位不同，后二位是00
而最后一级，区一级的，前二位与省级一样，中间与市级一样，最后二位是自己的号。