标题：asp.net联动列表框
简介
另类无刷新、联动下拉列表框（二级+XMLHttpRequest)
二级的联动下拉列表，从思路上讲，大致分下列几步：
一：触发第一个下拉列表的onchange事件。
二：异步调用处理页后，会返回处理请求后的信息（服务器端用Response.Write方法写入要返回的字符串，客户端用responseText属性接收字符串。
三：用得到的字符串处理后更新第二个下拉列表框
主要代码
如下：
一：建立读取XML的类，这里也可以是数据库的查询
public class ReadXmlCS
{
public const string k = "|";
public const string s = ",";
public ReadXmlCS()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
public static string QueryXml(string filename,string querystr)// @"//Pro_class/@id"
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
System.Xml.XPath.XPathDocument myXPathDocument = new System.Xml.XPath.XPathDocument(filename);
System.Xml.XPath.XPathNavigator myXPathNavigator = myXPathDocument.CreateNavigator();
try
{
System.Xml.XPath.XPathNodeIterator myXPathNodeIterator = myXPathNavigator.Select(querystr);
while(myXPathNodeIterator.MoveNext())
{
sb.Append(myXPathNodeIterator.Current.Value.ToString() +",");//把属性值添加到字符串末尾，添加分组字符“，”
System.Xml.XPath.XPathNavigator myXPathNavigator2 = myXPathNodeIterator.Current.Clone();//克隆当前接点
//     while(myXPathNavigator2.MoveToNextAttribute())//移动指针到下一个属性
//     {
//      sb.Append(myXPathNavigator2.Value.ToString()+"|");//把属性值添加到字符串末尾，添加分组字符“|”
//     }
myXPathNavigator2.MoveToNextAttribute();
sb.Append(myXPathNavigator2.Value.ToString()+"|");
}
return sb.ToString();
}
catch{return null;}
}
public static void QueryXml(string filename,string querystr,System.Web.UI.WebControls.DropDownList dd)// @"//Pro_class/@id"
{
System.Xml.XPath.XPathDocument myXPathDocument = new System.Xml.XPath.XPathDocument(filename);
System.Xml.XPath.XPathNavigator myXPathNavigator = myXPathDocument.CreateNavigator();
try
{
System.Xml.XPath.XPathNodeIterator myXPathNodeIterator = myXPathNavigator.Select(querystr);
while(myXPathNodeIterator.MoveNext())
{
System.Web.UI.WebControls.ListItem li = new System.Web.UI.WebControls.ListItem();
li.Value = myXPathNodeIterator.Current.Value.ToString() ;//把属性值(id)添加到ListItem的“值”属性
System.Xml.XPath.XPathNavigator myXPathNavigator2 = myXPathNodeIterator.Current.Clone();//克隆当前接点
//     while(myXPathNavigator2.MoveToNextAttribute())//移动指针到下一个属性
//     {
//      li.Text = myXPathNavigator2.Value.ToString();//把属性值(title)添加到ListItem的“文本”属性
//     }
myXPathNavigator2.MoveToNextAttribute();
li.Text = myXPathNavigator2.Value.ToString();
dd.Items.Add(li);
}
}
catch{}
}
}
其中关键的步骤加了注释，其它的大家可以到MSDN上去查找。
二。实现 （WebForm8.aspx.cs页面）：
protected System.Web.UI.WebControls.DropDownList DropDownList2;
protected System.Web.UI.WebControls.DropDownList Dropdownlist1;
private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
string str = this.Request.QueryString["querychild"];
if((str != null) && (str == "yes"))
{
string querystr = "//Pro_class[" + this.Request["parentid"] + "]/Pro_class_small/@id";
string show = zlp.str.ReadXmlCS.QueryXml(@"D:\Inetpub\wwwroot\zlp\XmlData\ProductMenu.xml",querystr);
this.Response.Write(show);
this.Response.End();
}
if(!this.IsPostBack)
{
this.BindDropDownList();//加载页面时，填充第一个下拉列表框
}
}
protected void BindDropDownList()
{
this.Dropdownlist1.Attributes.Add("onchange","javascript:XmlPost(this);"); //服务器端添加属性
zlp.str.ReadXmlCS.QueryXml(@"D:\Inetpub\wwwroot\zlp\XmlData\ProductMenu.xml",@"//Pro_class/@id",this.Dropdownlist1);
}