问在extjs中的折叠面板更改上要收听什么事件？

EN

Ext.create('Ext.panel.Panel', {
title: 'Accordion Layout',
width: 300,
height: 300,
layout:'accordion',
defaults: {
    // applied to each contained panel
    bodyStyle: 'padding:15px'
},
layoutConfig: {
    // layout-specific configs go here
    titleCollapse: false,
    animate: true,
    activeOnTop: true
},
items: [{
    title: 'Panel 1',
    html: 'Panel content!',
    listeners: {
        afterrender: function(thisCmp, eOpts) //(Ext.Component this, Object eOpts ) {
            // do what you want to do here
        }
    }
},{
    title: 'Panel 2',
    html: 'Panel content!'
},{
    title: 'Panel 3',
    html: 'Panel content!'
}],
renderTo: Ext.getBody()
});