datefield日期选择框，设置最大值最小值边界

{      xtype:"datefield",      margin : '5 5 5 5',      id : 'startDate',      name : 'q_startDate',      format:"Y-m-d",         fieldLabel:"起始时间",       emptyText : "请选择",      editable: false,      columnWidth : 1/3,      maxValue:new Date() ,      listeners:{expand:function(){var endDate = Ext.getCmp('endDate').getValue();if(endDate!=null){this.setMaxValue(endDate);}}}      },{      xtype:"datefield",      margin : '5 5 5 5',      id : 'endDate',      name:'q_endDate',      format:"Y-m-d",         fieldLabel:"截止时间",      emptyText : "请选择",      editable: false,      columnWidth : 1/3,      maxValue:new Date(),      listeners:{      expand:function(){var startDate = Ext.getCmp('startDate').getValue();if(startDate!=null){this.setMinValue(startDate);}}}      }