//绑定课程信息

        function changeDDl() {

            $.ajax({

                type: "post",

                url: "ChangeZsdHandler.ashx",

                data: "username=" + $.trim($("#hidUserName").val()),

                datatype: "text",

                success: function (data) {

                    if (data != "") {

                        $("#ddlKc").append(data);

                    }

                }

            });

        }

<select id="ddlKc">

</select>

Ajax中代码

if (context.Request["username"] != null)

        {

            username = context.Request["username"].ToString();

            DataTable dt = kmbll.BindKc(username);

            StringBuilder sbOptione = new StringBuilder();

            sbOptione.Append("<option value=http://www.mamicode.com/‘0‘> ===请?选?择?课?程¨¬=== ");

            if (dt != null)

            {

                if (dt.Rows.Count > 0)

                {

                    foreach (DataRow dr in dt.Rows)

                    {

                        sbOptione.Append("<option value=http://www.mamicode.com/"" + dr["kmId"] + "\">" + dr["kmName"] + "</option>");

                    }

                }

            }

            context.Response.Write(sbOptione.ToString());

        }

        else

        {

            context.Response.Write("");

        }

        context.Response.End();

使用ajax绑定下拉列表