Extjs 如何动态添加window的items项

JScript code
<script type="text/javascript"> 

var user1 = new Ext.form.TextField({ })

var user2= new Ext.form.TextField({ })

var c_window = new Ext.Window({
       title: 'title',
        width: 950,
        height: 530,
        plain: true,
        closeAction: 'hide',
        defaults: { anchor: '95%' },
        items:[user1],
        modal: true,
        buttons: [{ text: '关闭', handler: function(){ c_window.hide(); } },
        { text: '添加',
        handler: function(){
        c_window.add(user2); // 添加新组件
        c_window.render(); // 添加后需要重新渲染一遍。 } }] });

c_window.show();
</script>