<script language="javascript" src="Js/prototype.js"></script>

<script language="javascript">

function GetCityList()
    {
        var pid = $('areacity').value
        var url = "http://localhost:53156/WebSite/asmx/UserWebService.asmx/GetCityByRoorID";
        var pars = 'rootid='+pid;
        var myajax = new Ajax.Request(url,{method:'post',postBody:pars,onComplete:showResponseCity});
       
    }
    function showResponseCity(request)
    {
        //alert(request.responseText.replace(/&lt;/g,"<").replace(/&gt;/g,">"));
        var objXml = request.responseText.replace(/&lt;/g,"<").replace(/&gt;/g,">");
        var myDocument = new ActiveXObject("Microsoft.XMLDOM")
        myDocument.async="false";
        myDocument.loadXML(objXml);
        var nodeList=myDocument.documentElement.getElementsByTagName("ds");
        //alert(nodeList.length);
        var innertext="";
        for(i=0;i<nodeList.length;i++)
        {
            innertext=innertext+"<a href=# onclick=javascript:cancel();SelectCity('"+nodeList(i).selectSingleNode("AreaName").text+"');CloseDiv('CityBigDiv')>"+nodeList(i).selectSingleNode("AreaName").text+"</a>&nbsp;&nbsp;&nbsp;&nbsp;";
        }
        $("CityDiv").innerHTML = innertext;
    }

</script>

=====html=======

<div id="PrDiv"><select name="areacity" id="areacity" onchange="GetCityList()">
<option value="0">直辖市</option>
<option value="4">广东省</option>
</select></div>
<a href="#" onclick="javascript:cancel();CloseDiv('CityBigDiv');">关闭</a>
<div id="CityDiv"></div>
</div>

================

========webservice=======

[WebMethod]
    public string GetCityByRoorID(int rootid)
    {
        string wherestr = " AreaFollowid=" + rootid ;
        if (rootid==0)
        {
            wherestr += " and IsALineCity=1";
        }
        DataSet ds = zhangbenproject.Common.AreaTableFactory.GetList(wherestr);
       
        string xmlstr = ds.GetXml();
        return xmlstr;
    }

===========================