extjs girdpanel中的数据为何不显示？专家帮帮忙！

Ext.define('S3.Console.HealthReport1', {
    constructor: function () {        var startDate = Ext.create('Ext.form.field.Date', {
            fieldLabel: '开始时间',
            format: 'Y/m/d',
            editable: false,
            value: Ext.Date.add(new Date(), Ext.Date.DAY, -7),
            labelWidth: 80,
            width: 200
        });        var endDate = Ext.create('Ext.form.field.Date', {
            fieldLabel: '结束时间',
            format: 'Y/m/d',
            editable: false,
            value: new Date(),
            labelWidth: 80,
            width: 200
        });        var store = new Ext.data.JsonStore({
            root: 'data'
        });
        var grid = Ext.grid.GridPanel({
            height: 350,
            width: 600,
           data:store
        });
        var panel = Ext.create('Ext.panel.Panel', {
            width: 600,
            height: 500,
            layout: {
                type: 'fit',
                columns: 1
            },
            items: grid,
            buttons: [
              { text: '立即体检',
                  width: 150,
                  height: 50,
               
                  handler: function () {                      Ext.Ajax.request({
                          url: 'core/WebService.asmx/ColdStorage',
                          headers: {
                              'Content-Type': 'application/json; charset=utf-8'
                          },
                          method: 'POST',
                          jsonData: {
                              startTime: Ext.Date.format(startDate.getValue(), 'Y-m-d'),
                              endTime: Ext.Date.format(endDate.getValue(), 'Y-m-d') + ' 23:59:59.999',
                              dept_id: "0002"
                          },
                          success: function (response) {
                              var responseJson = Ext.JSON.decode(response.responseText);
                              store.loadData(responseJson);
                             // Ext.Msg.alert("dsd");                             
                          },
                          failure: function () { Ext.Msg.alert("错误"); }                      });                  }
              }
            ]        });
        var win = new Ext.create('Ext.Window', {
            title: '报表',
            height: 500,
            width: 600,
            layout: 'fit',
            tbar: [startDate, endDate],
            items: panel
        })        win.show();
    }});