Ext.form.ComboBox 提交始终获得displayField的值

var returnComBox = new Ext.form.ComboBox({
                    id:'isReturnCom',
                    fieldLabel:'是否已退款',
                    triggerAction:'all',
                    store:new Ext.data.SimpleStore({
                        fields:['isReturnText','isReturnNum'],
                        data:[['全部','2'],['已退款','1'],['未退款','0']]
                    }),
                    hiddenName:'isReturn',//提交到后台的input的name
                    displayField:'isReturnText',
                    valueField:'isReturnNum',
                    mode:'local',
                    forceSelection:true,
                    resizable:false,
                    value:'2',
                    width : 100
                });

重要属性设置 hiddenName:'isReturn'。  后台直接通过 String alertLevel = request.getParameter("isReturn");获取值