在Asp.net网站开发中，常用到的一个技术是省市县无刷新级联，本来采用AJAX来实现，并附有详细代码
<form id="form1" runat="server">
    <div>
        <div id="dv">
        <table>
            <tr>
            <td><asp:DropDownList ID="ddlProvince" runat="server" onchange="ProvinceChange()"></asp:DropDownList></td>
            <td><select ID="ddlCity" runat="server" onchange="CityChange()"></select></td>
            <td><select ID="ddlArea" runat="server"></select></td>
            </tr>
        </table>
            <br />
            <asp:Button ID="Button1" runat="server" OnClick="Button1_Click1" Text="查看省市县" /></div>
    <script>
        
        function ProvinceChange()
        {
            var obj = document.getElementById("ddlProvince").options[document.getElementById("ddlProvince").selectedIndex];
            var city = document.getElementById("ddlCity");
            var area = document.getElementById("ddlArea");
            var strcitys =  _Default.getParent(obj.value).value;
            if(strcitys.indexOf(",")>0)
            {
                city.length=0;
                city.options[0] = new Option("请选择","-1");
                area.length=0;
                area.options[0] = new Option("请选择","-1");
                var citys = strcitys.split("-");
                for(var i=0;i<citys.length;i++)
                {
                    city.options[i+1] = new Option(citys[i].split(",")[0], citys[i].split(",")[1]);
                }
            }
            else
            {
                city.length=0;
                city.options[0] = new Option("请选择","-1");
            }
        }
        
         function CityChange()
        {
            var obj = document.getElementById("ddlCity").options[document.getElementById("ddlCity").selectedIndex];
            var city = document.getElementById("ddlArea");
            var strcitys =  _Default.getParent(obj.value).value;
            if(strcitys.indexOf(",")>0)
            {
                city.length=0;
                city.options[0] = new Option("请选择","-1");
                var citys = strcitys.split("-");
                for(var i=0;i<citys.length;i++)
                {
                    city.options[i+1] = new Option(citys[i].split(",")[0], citys[i].split(",")[1]);
                }
            }
            else
            {
                city.length=0;
                city.options[0] = new Option("请选择","-1");
            }
        }
    </script>
    </div>
    </form>

CS代码如下：

public sqlDMO sqldmo = new sqlDMO();

    protected void Page_Load(object sender, EventArgs e)
    {
        
        if (!IsPostBack)
        {
            setProvince();
            ListItem listCity = new ListItem("请选择", "-1");
            ddlCity.Items.Insert(0, listCity);
            ListItem listArea = new ListItem("请选择", "-1");
            ddlArea.Items.Insert(0, listArea);
        
        }
        AjaxPro.Utility.RegisterTypeForAjax(typeof(_Default));
    }

    private void setProvince()
    {
        DataTable dtProvince = sqldmo.Query("select ass_id as id,ass_dis as name from assort where ass_name='province'");
        ddlProvince.DataSource = dtProvince;
        ddlProvince.DataTextField = "name";
        ddlProvince.DataValueField = "id";
        ddlProvince.DataBind();
        ListItem listProvince = new ListItem("请选择", "-1");
        ddlProvince.Items.Insert(0, listProvince);
    }

    [AjaxPro.AjaxMethod]
    public string getParent(string parentID)
    {
        DataTable dtCity = sqldmo.Query("select ass_id as id,ass_dis as name from assort where ass_fid='" + parentID + "'");
        string strCity = "";
        for (int i = 0; i < dtCity.Rows.Count; i++)
        {
            strCity += dtCity.Rows[i]["name"].ToString().Trim() + "," + dtCity.Rows[i]["id"].ToString().Trim() + "-";
            if (i == dtCity.Rows.Count - 1) strCity = strCity.Substring(0, strCity.Length - 1);
        }
    
        return strCity;
    }