extjs Array Grid 怎么分页没有效果?

//数据源，用来定义表格中要显示的数据
Ext.onReady(function(){
var dataSource=[
["zhangsan",12,"boy"],
["lisi",20,"boy"],
["xiaocheng",18,"girl"],
["zhangxiao",12,"boy"],
["liwu",20,"boy"],
["xiangyang",18,"girl"],
["gao",12,"boy"],
["lisi",20,"boy"],
["xiaoli",18,"girl"]
];


//用来创建一个数据存储
var ds=new Ext.data.Store({
data:dataSource,
reader:new Ext.data.ArrayReader({},[
{name:'name'},
{name:'age',type:'float'},
{name:'sex'},
])
});
ds.loadData(dataSource);

//多选框
var sm=new Ext.grid.CheckboxSelectionModel();
//定義column模型
var colmodel=new Ext.grid.ColumnModel(
[new Ext.grid.RowNumberer(),//自动显示行号
sm,
{header:'name',width:120,sortable:true,dataIndex:'name',editor:new Ext.form.TextField()},
{header:'age',width:120,sortable:true,dataIndex:'age',editor:new Ext.form.TextField()},
{header:'sex',width:120,sortable:true,dataIndex:'sex',
editor:new Ext.grid.GridEditor(new Ext.form.TextField({
allowBlank:false
}))},
]);



//编辑grid
  var grid=new Ext.grid.EditorGridPanel({
renderTo:"grid-example",
store:ds,
colModel:colmodel,
  sm:sm,
title:"my is title",
width:380,
height:200,
autoExpandColumn:2,
enableColLock:false, 
clicksToEdit:2,//双击才能编辑
//实现分页 disp ayInfo：ture 但是displayMsg中信息实现不出来？？
  bbar:new Ext.PagingToolbar({
pageSize:5,//设置每页显示的大小但是不管用
store:ds,
displayInfo:true,
displayMsg:'显示第{0}条到第{1}条记录,一共{2}条',
emptyMsg:"没有记录"
  })
  });

 
});

分页没有效果，而且多选框也没有效果，求高手指点

我记得extjs Array Grid不支持分页的