extjs4怎么刷新<iframe>?

var tab = Ext.create('Ext.TabPanel', {

        id:'myTabPanel',
        region:'center',
        layout: 'fit',
        itemId: 'center-tabs',

        items : [{ 
            id:'home',
            title : "Home Page",
            iconCls: 'House',
            html : '<iframe src= "jsp/homepage.jsp" width="100%" height="100%" marginwidth="0" framespacing="0" marginheight="0" frameborder="0" ></iframe>',
            /*loader: { url:'jsp/homepage.jsp', loadMask: 'loading...', autoLoad: true, scripts: true },*/
            listeners:{         
            activate:function(tab){ 
            }  
                 }

        }]
    });

试了好多方法都没用

this.loader.load();
tab.getUpdater().refresh();
this.getActiveTab().refresh();