ExtJS 异步加载树节点

var Tree_Item = Ext.tree;
    //定义根节点的Loader
    if (treepanelItem == undefined) {
        treepanelItem = new Tree_Item.TreePanel({
          el: 'tree_tab_Itme',   //填充区域 
            rootVisible: true,     //隐藏根节点 
            border: true,          //边框 
            animate: true,         //动画效果 
            autoScroll: true,      //自动滚动 
            enableDD: false,       //拖拽节点              
            containerScroll: true,
            loader: new Ext.tree.TreeLoader({
                directFn: Led.LiYan.LoadInfo //后台方法
            })
        });
    }
    var rootnodeItme = treepanelItem.getRootNode();
    if (rootnodeItme == undefined) {
        //异步加载根节点 
        rootnodeItme = new Tree_Item.AsyncTreeNode({
            id: listid,//方法传入的参数
            text: '节目清单'
        });
        treepanelItem.setRootNode(rootnodeItme);
    }
    else {
        rootnodeItme.removeAll();
        rootnodeItme.id = listid;
        rootnodeItme.reload();
    }
    //设置根节点 
    //响应事件，传递node参数 
    treepanelItem.on('beforeload', function (node) {
        treepanelItem.loader.directFn = Led.LiYan.LoadInfo;    //定义子节点的Loader    
    });
    treepanelItem.render();
    rootnodeItme.expand(true, false);