ajax,asp用dropdownlist动态显示树形结构

控件页面代码

<div id="appear" runat="server">
<asp:DropDownList ID="ddlFather" runat="server" onchange="go(this)" ></asp:DropDownList>
</div>
<input id="Ids" type="hidden" runat="server"/>
<input id="tName" type="hidden" runat ="server" />

<script type="text/javascript">

var xmlHttpRequest = null;

function go(obj)
{  
    var dropdown=document.getElementById("<%=appear.ClientID %>");
    var delid=0;
    while(document.getElementById("<%=this.ClientID %>"+delid)!=null){            
        dropdown.removeChild(document.getElementById("<%=this.ClientID %>"+delid));
        delid++;
    }
    var value=obj.value;
    var tName=document.getElementById("<%=tName.ClientID %>").value;
    var url="/comm/setclass/getsons.ashx?tname="+tName+"&id="+value;
        
    if (window.ActiveXObject) 
    {
        xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");
    }
    else 
    {
        xmlHttpRequest = new XMLHttpRequest();
    }
    
    xmlHttpRequest.onreadystatechange = function(){readyDo(0);};
    xmlHttpRequest.open("GET", url, true);
    xmlHttpRequest.send();
}
function readyDo(idCount)
{

    if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) {
        var vSons = xmlHttpRequest.responseText;
        var JsonSons=eval(vSons);
        disPlay(JsonSons,idCount);
        //ShowDrop(JsonSons,0);
    }
}

function disPlay(sons,idCount){
    var dropdown=document.getElementById("<%=appear.ClientID %>");
    var select=document.createElement("select");
    select.id="<%=this.ClientID %>"+idCount++;
    select.onchange=function(){
        //delete
        var delid=idCount;
        while(document.getElementById("<%=this.ClientID %>"+delid)!=null){            
            dropdown.removeChild(document.getElementById("<%=this.ClientID %>"+delid));
            delid++;
        }
        
        var value=select.value;
        var tName=document.getElementById("<%=tName.ClientID %>").value;
        var url="/comm/setclass/getsons.ashx?tname="+tName+"&id="+value;
        if (window.ActiveXObject) {
            xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");
        }
        else {
            xmlHttpRequest = new XMLHttpRequest();
        }
        xmlHttpRequest.onreadystatechange = function(){readyDo(idCount);};
        xmlHttpRequest.open("GET", url, true);
        xmlHttpRequest.send();
    }
    //new
    for(var i=0;i<sons.length;i++){
        select.options[i]=new Option(sons[i].name,sons[i].id);
    }    
    dropdown.appendChild(select);
}
</script>

ashx.cs代码

public class getsons : System.Web.UI.Page
    {
        public void Page_Load(object sender, EventArgs e)
        {
            Response.ContentType = "text/plain";
            Response.Write(getSonById());
        }
        public string getSonById()
        {
            string strId=Request["id"];
            string strTableName=Request["tName"];
            ClsTbProc clsSrc = new ClsTbProc(GlbDef.GetDbConnStr(), strTableName);
            DataTable dt = clsSrc.GetRec("fId,fName", "where fParentId='" + strId + "'");
            if (dt == null || dt.Rows.Count == 0)
            {
                return null;
            }
            string strJson = "[{\"name\": \"----\", \"id\": \"----\"},";
            foreach (DataRow dr in dt.Rows)
            {
                string strNameSon=dr["fName"].ToString();
                string strIdSon=dr["fId"].ToString();
                strJson += "{\"name\": \"" + strNameSon + "\", \"id\": \"" + strIdSon + "\"},";
            }
            strJson = strJson.Trim(',') + "]";
            return strJson;
        }
    }