下拉框二级联动，页面无刷新

A. (aspx)

             
      
       请选择
              
      
       北京
              
      
       天津
              
      
       湖北
          
         
         
         
 

B.(cs 文件)

 1.  实现ICallbackEventHandler 接口

2.向客户端注册回传方法protected void Page_Load(object sender, EventArgs e){   //向客户端注册事件 ClientCallback，ClientCallbackError 前台页面实现的JavaScript方法   string callBack = Page.ClientScript.GetCallbackEventReference(this, "arg", "ClientCallback", "context", "ClientCallError", false);   string clientFunction = "function getChildren(arg,context){
    "+callBack+";};";   Page.ClientScript.RegisterClientScriptBlock(this.GetType(),"getChildren",clientFunction,true);}//3.实现接口两个方法string callBackResult = "";public string GetCallbackResult(){   return callBackResult;}     public void RaiseCallbackEvent(string eventArgument){    switch (eventArgument)   {         case "BJ":             callBackResult = "One|Two|Three";             break;        case "TJ":             callBackResult = "Four|Five|Six";             break;        case "HB":             callBackResult = "Seven|Eight|Nine";              break;        default :             callBackResult = "";             break;  }}