asp.net中js+jquery添加下拉框值和后台获取

html xmlns="http://www.w3.org/1999/xhtml"
head runat="server"
    title /title
    script src="Scripts/jquery-1.4.1.js" type="text/javascript" /script
    script type="text/javascript"
        $(function () {
            $(".cg2").change(function () {
                var id = $(this).attr("id");
                var value = $(this).val();
                var newid = #+id.replace(_1_, _2_);//把第一列id替换成第二列id
                //alert(newid);
                var data = "t1*v1|t2*v2|t3*v3";//后台获取的数据格式，这里用固定值了
                var datas = data.split(|);//分割成多组
                for (var i = 0; i datas.length; i++) {
                    var d1 = datas[i].split(*);//每组分割成 显示值和真实值
                    $(newid).append(" option value=\""+d1[1]+"\" " + d1[0] + " /option
                    //alert(d1);
                }
               // alert(id + "|||" + value);
            });
        })
       
    /script
/head
body
    form id="form1" runat="server"
    div 为了满足两列，任意多行。后台动态生成下拉框，还要前后列联级的需求。使用js+jquery，用服务器控件+Ajax也不行，老是选择之后就
        asp:DropDownList ID="ddl_1_1" Css runat="server"
        asp:ListItem Text="txt1" Value="val1" /asp:ListItem
        asp:ListItem Text="txt1" Value="val1" /asp:ListItem
        asp:ListItem Text="txt1" Value="val1" /asp:ListItem
        /asp:DropDownList
        asp:DropDownList ID="ddl_2_1" runat="server"
        /asp:DropDownList br/
        asp:DropDownList ID="ddl_1_2" Css runat="server"
        asp:ListItem Text="txt2" Value="val2" /asp:ListItem
        asp:ListItem Text="txt2" Value="val2" /asp:ListItem
        asp:ListItem Text="txt2" Value="val2" /asp:ListItem
        /asp:DropDownList
        asp:DropDownList ID="ddl_2_2" runat="server"
        /asp:DropDownList br/
        asp:Button ID="ButtonGet" runat="server" Text="获取" /
        asp:Label ID="Label1" runat="server" Text="" /asp:Label
    /div
    /form
/body
/html

//后台

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {

            }
        }

        protected void ButtonGet_Click(object sender, EventArgs e)
        {
            ///获取通过js加选择的 ddl_2_1 控件选中的值，显示在Label1上。
            Label1.Text = Request["ddl_2_1"].ToString();
        }