ASP.net DropDownList 无刷新联动菜单

再谈 N 个 asp.net DropDownList 无刷新联动菜单，牺牲N-1个ASPX来实现自动更新机制，避免刷新的闪动！！以下代码绝对可以使用，也可以实现多级菜单。。。。

function load(state)
{
var drp2 = document.getElementById("DropDownList2");
for(var i=0;i<=drp2.options.length-1;i++)
{
drp2.remove(i);
}
var oHttpReq = new ActiveXObject("MSXML2.XMLHTTP"); //发送请求
var oDoc = new ActiveXObject("MSXML2.DOMDocument"); //响应结果
var state=document.getElementById("DropDownList1").value;
oHttpReq.open("post","webform6.aspx?state="+state, false);
oHttpReq.send("");
result = oHttpReq.responseText;
oDoc.loadXML(result);　

// items = oDoc.selectNodes("//CITY/Table");
items = oDoc.selectNodes("//address/Table");
　　 for (var item = items.nextNode();item;item = items.nextNode())
　　 {　
　　 　var city = item.selectSingleNode("//address").nodeTypedValue;
　　 　var newOption = document.createElement("OPTION");　
　　 　newOption.text = city;　
　　 　newOption.value = city;　
　　 　drp2.options.add(newOption);　
　　 　 }　
}
<script language="javascript">
function load(state)
{
var drp2 = document.getElementById("DropDownList2");
for(var i=0;i<=drp2.options.length-1;i++)
{
drp2.remove(i);
}
var oHttpReq = new ActiveXObject("MSXML2.XMLHTTP"); //发送请求
var oDoc = new ActiveXObject("MSXML2.DOMDocument"); //响应结果
var state=document.getElementById("DropDownList1").value;
oHttpReq.open("post","webform2.aspx?state="+state, false);
oHttpReq.send("");
result = oHttpReq.responseText;
oDoc.loadXML(result);　

// items = oDoc.selectNodes("//CITY/Table");
items = oDoc.selectNodes("//address/Table");
　　 for (var item = items.nextNode();item;item = items.nextNode())
　　 {　
　　 　var city = item.selectSingleNode("//address").nodeTypedValue;
　　 　var newOption = document.createElement("OPTION");　
　　 　newOption.text = city;　
　　 　newOption.value = city;　
　　 　drp2.options.add(newOption);　
　　 　 }　
}
</script>

============================
webform1.aspx
private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
if(!IsPostBack)
{
SqlConnection con = new SqlConnection("packet size=4096;user id=sa;data source=SERVER;persist security info=False;initial catalog=pubs");
SqlDataAdapter da = new SqlDataAdapter("select state from authors group by state",con);
DataSet ds = new DataSet("State");
da.Fill(ds);
this.DropDownList1.DataSource = ds.Tables[0];
this.DropDownList1.DataTextField = "state";
this.DropDownList1.DataValueField = "state";　
this.DropDownList1.DataBind();　　
this.DropDownList1.Attributes.Add("onchange","load()");　　
//DropDownList1.
}

}

webform2.aspx
private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
if(this.Request["state"]!=null)
{　　
string state = this.Request["state"].ToString();　　
SqlConnection con = new SqlConnection("packet size=4096;user id=sa;data source=SERVER;persist security info=False;initial catalog=pubs");
SqlDataAdapter da = new SqlDataAdapter("select address from authors where state = '"+state+"'",con);　　
DataSet ds = new DataSet("address");　　
da.Fill(ds);　　
XmlTextWriter writer = new XmlTextWriter(Response.OutputStream, Response.ContentEncoding);　　
writer.Formatting = Formatting.Indented;　　
writer.Indentation = 4;　　
writer.IndentChar = ' ';　　
ds.WriteXml(writer);　　
writer.Flush();　　
Response.End();　　
writer.Close();　　
}
}