ext4.2 gridpanel显示数据有关问题

ext4.2 gridpanel显示数据问题
extjs新手。
我照着网上的例子,写的代码。其实就是后台拿到数据集并转换为json字符串,前台store获取字符串并加载到gridpanel里边。gridpanel是出来了,但是数据显示不出来。
上代码:
前台gridpanel:
var GuestInfogrid = new Ext.grid.GridPanel({
xtype: "grid",
region: "center",
id: "gd_User",
header: false,
columns: [
{
header: "ID", sortable: true, dataIndex: "ID", width: 30, hidden: true
},
{
header: "登录名", sortable: true, dataIndex: "F_LOGINNAME", width: 100
},
{
header: "真实姓名", sortable: true, dataIndex: "F_REALNAME", width: 100
},
{
header: "角色", sortable: true, dataIndex: "F_ROLENAME", width: 50
},
{
header: "创建时间", sortable: true, dataIndex: "F_CREATE_TIME", width: 100, renderer: renderDate
},
{
header: "更新时间", sortable: true, dataIndex: "F_UPDATE_TIME", width: 100, renderer: renderDate
},
{
header: "状态ID", sortable: true, dataIndex: "F_ACTIVEFLAG", width: 10, hidden: true
},
{
header: "状态", sortable: true, dataIndex: "ACTIVEFLAG", width: 50
},
{
header: "备注", sortable: true, dataIndex: "F_MEMO", width: 200
}
],
store: UserInfor,
border: 0,
loadMask: { msg: '加载数据中,请等待......' }
})

前台 store获取数据
//分页每页显示数量
var pageSize = 12;
//指定列参数
var fields = ["ID", "F_LOGINNAME", "F_REALNAME", "F_ROLENAME", "F_CREATE_TIME", "F_UPDATE_TIME", "F_ACTIVEFLAG", "ACTIVEFLAG", "F_MEMO"];
//获取后台
var UserInfor = Ext.create('Ext.data.Store', {
pageSize: pageSize,  //分页大小
//model: 'rukuInfos',
fields:fields,
proxy: {
param: { Sys_User: "GetUser" },
type: 'ajax',
method: 'POST',
url: "/Url/Sys/Sys_User.aspx",//请求的地址
reader: { root: 'alluser', totalProperty: 'totalCount' }
}
});//

前台可以调用后台代码,传上来的字符串如下:
{totalCount:3,success:true,error:"",singleInfo:"",alluser:[{"_activeflag":null,"_f_activeflag":"正常","_f_create_time":"\/Date(1411626268000+0800)\/","_f_loginname":"yaoxiaojun","_f_memo":"beizhu","_f_password":null,"_f_realname":"姚晓军","_f_role_id":null,"_f_update_time":"\/Date(1411626268000+0800)\/","_id":2},{"_activeflag":null,"_f_activeflag":"正常","_f_create_time":"\/Date(1415779771000+0800)\/","_f_loginname":"ceshi","_f_memo":"","_f_password":null,"_f_realname":"测试","_f_role_id":null,"_f_update_time":"\/Date(1415782992000+0800)\/","_id":30},{"_activeflag":null,"_f_activeflag":"不可用","_f_create_time":"\/Date(1415781590000+0800)\/","_f_loginname":"2343","_f_memo":"","_f_password":null,"_f_realname":"345","_f_role_id":null,"_f_update_time":null,"_id":31}]}

求帮忙


------解决思路----------------------
你好!
你后台传过来的列是有下划线的_id,__f_create_time的,而你的filed有些没有_(下划线),id,ACTIVEFLAG,前后要统一。