extjs4 分页工具栏pagingtoolbar的每页显示数据combobox下拉框

var itemsPerPage = 20;
var combo;
//创建数据源store
Ext.define('recordStore', {
			extend : 'Ext.data.Store',
//			autoLoad : {
//				start : 0,
//				limit : itemsPerPage
//			},
			start : 0,
			limit : itemsPerPage,
			pageSize : itemsPerPage,
			model : 'recordModel',
			proxy : {
				// 异步获取数据。这里的URL能够改为不论什么动态页面，仅仅要返回JSON数据就可以
				type : 'ajax',
				url : '../drivingrecord/driveingInfoList.do',
				reader : {
					type : 'json',
					root : 'serials', // 返回信息的根名称。为必选项
				//	idProperty : 'id', // 数据唯一标识字段
					successProperty : 'success',
					totalProperty : "total"//总记录数
				}
			}
		});

//分页的combobox下拉选择显示条数
	 combo = Ext.create('Ext.form.ComboBox',{
	      name: 'pagesize',
	      hiddenName: 'pagesize',
	      store: new Ext.data.ArrayStore({
	          fields: ['text', 'value'],
	          data: [['20', 20], ['40', 40],['60', 60], ['80', 80], ['100', 100]]
	      }),
	      valueField: 'value',
	      displayField: 'text',
	      emptyText:20,
	       50
	  });//若要“永久性”更改全局变量itemsPerPage，此combox要放在Ext.onReady(）;中

//加入下拉显示条数菜单选中事件
	 combo.on("select", function (comboBox) {
	 <span style="white-space:pre">	</span>var pagingToolbar=Ext.getCmp('pagingbar');
	 	pagingToolbar.pageSize = parseInt(comboBox.getValue());
	    itemsPerPage = parseInt(comboBox.getValue());//更改全局变量itemsPerPage
	    recordStore.pageSize = itemsPerPage;//设置store的pageSize，能够将工具栏与查询的数据同步。
	    
	    recordStore.loadPage(1);//显示第一页,不论你在第几页又一次选择显示条数，默认都显示第一页数据，rowNumber也会自己主动转换成从1開始。

	    
	 });
//为grid添加分页工具栏
dockedItems : [{
											id:'pagingbar',
											xtype : 'pagingtoolbar',
											store : recordStore,
											dock : 'bottom',
											displayInfo : true,
											autoScroll : true,
											beforePageText : "第",// update
											afterPageText : "页  共 {0} 页",// update
											firstText : "第一页",
											prevText : "上一页",// update
											nextText : "下一页",
											lastText : "最后页",
											refreshText : "刷新",
											displayMsg : "显示 {0} - {1}条，共 {2} 条",// update
											emptyMsg : '没有数据',
											items: ['-', '每页显示',combo,'条']//此处是将创建的combobox加入到工具栏中
										}]

后台传回json数据：

{"total":29,"serials":[{"endNewOilCost":0,"endMileage":2.11960465E8,"endLatitude":"32.234183","beginMileage":2.11960465E8,"statusType":"PARK","beginDescription":"江苏省南京市栖霞区麒麟广场(南京)东南1.1公里","beginLongitude":"118.779383","beginTimeAsStr":"00:01:08","avelocity":"","sendDateAsStr":"2014-07-01","endTime":-24322000,"endDateAsStr":"1970-01-01 01:14:38","time":"1小时13分钟30秒","endOilCost":0,"carid":"苏AF1185","sendtime":"","msgid":270003281,"begintimeStr":"2014-07-01 00:01:08","beginOilCost":0,"mileage":"","status":2,"endDescription":"江苏省南京市栖霞区麒麟广场(南京)东南1.1公里","beginTime":-28732000,"minVelocity":0,"endLongitude":"118.779403","endTimeAsStr":"01:14:38","beginDateAsStr":"1970-01-01 00:01:08","sendDate":{"nanos":0,"time":1404144000000,"minutes":0,"seconds":0,"hours":0,"month":6,"timezoneOffset":-480,"year":114,"day":2,"date":1},"timeclose":"1小时13分钟30秒","endtimeStr":"2014-07-01 01:14:38","maxVelocity":0,"beginNewOilCost":0,"statusAsString":"停车","serial":"15251782437","averageVelocity":"","beginLatitude":"32.234217"
}],"success":true}

效果例如以下：