Extjs Grid store加载数据

Extjs Grid store加载数据不会出来，网络跟踪能够开到数据已经查询到前台，可是就不显示，

代码如下

var contract_selectItem_storeBudget = new Ext.data.JsonStore({
proxy: new Ext.data.HttpProxy({
url: woo.constant.baseUrl+ "/AjaxPage/WooYuSuan/YusuanManager.aspx?cmd=list"
}),
reader: new Ext.data.JsonReader({
totalProperty: 'totalProperty',
root: 'List'
}, contract_selectItem_readerBudget)

});

修改后如下把JSONStore换成Store就出来了

var contract_selectItem_storeBudget = new Ext.data.Store({
        proxy: new Ext.data.HttpProxy({
            url: woo.constant.baseUrl+ "/AjaxPage/WooYuSuan/YusuanManager.aspx?cmd=list"
        }),
        reader: new Ext.data.JsonReader({
            totalProperty: 'totalProperty',
            root: 'List'
        }, contract_selectItem_readerBudget)

     
      
    });