Ext的viewport的有关问题

Ext的viewport的问题
我想点根1的时候，中间的页面换成另个panel，点根2的时候也换一个
代码：[code=JScript][/code]
  Ext.onReady(function(){
   
   
var root=new Ext.tree.TreeNode({
id:'root',
text:'树的根'
});
 
root.appendChild(new Ext.tree.TreeNode({
id:'c1',
text:"根1"}));
 
root.appendChild(new Ext.tree.TreeNode({
id:'c2',
text:"根2"  
}));
 
var tree=new Ext.tree.TreePanel({
title:'管理',
region:'west',
root:root,
width:100
});
   
var viewport=new Ext.Viewport({
layout:'border',
items:[{
region:'north',
height:60,
contentEl:'Ndiv'
},{
region:'south',
contentEl:'Sdiv'
},tree,{
region:'center',
id:'center',
html:'欢迎XXX'  
}]
});
 
 
   
  });

[解决办法]

JScript code

  Ext.onReady(function () {                var store = Ext.create('Ext.data.TreeStore', {                    root: {                        expanded: true,                        children: [{                            text: "c1",                            url:'http://www.baidu.com',                            leaf: true                        }, {                            text: "c2",                            url:'http://www.gougou.com',                            leaf: true                        }]                    },                    text:'root'                 });                var tree = Ext.create('Ext.tree.Panel', {                    title: 'Simple Tree',                    width: 200,                    height: 150,                    store: store,                    region: 'west',                    rootVisible: false,                    listeners:{                        itemclick:function(view,record){                            var panel = Ext.getCmp("center");                            var loader = panel.getLoader();                                alert(record.raw.url);                            loader.load({url:record.raw.url});                        }                    }                });                var viewport = Ext.create('Ext.container.Viewport', {                    layout: 'border',                    items: [{                        region: 'north',                        height: 60,                        html: 'Ndiv'                    }, {                        region: 'south',                        height: 60,                        html: 'Sdiv'                    },                    tree,                    {                        region: 'center',                        id: 'center',                       autoLoad:'http://www.hao123.com'                    }]                });            });