无限级二级菜单，越来越多的被应用，譬如省级->市级的二级菜单

思路：一级下拉列表select 绑定一个id， jqury获取到该下拉列表的checked属性值，通过ajax请求获取到该值所对应的二级内容，然后jquery修改二级下拉列表的内容，即可实现动态生成二级联动下拉列表

示例：

下拉列表

                <td width="40%">一级分类

                    <select id="head_one">                         <option value="-1">全部</option>                         <volist name="ones" id="val">                         <option value="{$val.id}">{$val.cname}</option>                         </volist>                     </select>                 </td>                 <td width="40%">二级分类                     <select id="head_two">                         <option value="-1">全部</option>                     </select>                 </td>

jqury post获取

        $("#head_one").change(function(){

            var parentId = $("#head_one").val();             if(parentId == -1)                 return false;             $.ajax({                 url : '{:U("Info/checkTwoCategory")}',                 type : 'POST',                 data : {                     'parentId' : parentId,                 },                 dataType : 'json',                 error:function()                 {                     alert('Error loading data!');                 },                 success:function(msg)                 {                     $("#head_two").empty();                       $.each(eval(msg), function(i, item) {                           $("<option value='" + item.id + "'>" + item.cname + "</option>").appendTo($("#head_two"));                     });                 }             });                      });

即可实现二级联动下拉列表