怎样拿到Viewprot中的 east对象,来控制它show和 hide

new Ext.Viewport({
        layout:"border",
        items:[
            {region:"west", width:150, title:"组织架构",  id:'tree',
                html:""},
            {region:"center",
                xtype:"tabpanel",
                activeTab: <%=activeTab%>,
                items:[
                    {title:"用户管理",iconCls:'user',listeners: {activate: activeUser},  id:'userTab',
                        html:""},
                    {title:"部门管理",iconCls:'group',listeners: {activate: activeGroup}, id:'groupTab',
                        html:""}
                ]
            },{region:"east",
                title:"用户权限",
                width:200,
                split:true,
                collapsible:true,
                minSize: 175,
                maxSize: Ext.lib.Dom.getViewHeight()-150,
                autoScroll:true,
                layoutConfig:{
                    animate:true},
                items:[{
                                border:false,
                                height:Ext.lib.Dom.getViewHeight()-150, //400, //有个固定高度树才可以显示
                                width:"", //设置为""才不会有滚动条
                                id:"tree-div" //将下面的树放在item中才不会有BUG
                        }]
        }
        ]
    });如题,我要得到Viewport中east的对象,好控制它的show 和hide先在这儿谢了！