Extjs treePanel 加载等待框

beforeload : {
fn : function (store, operation, eOpts){
loadMask = new Ext.LoadMask(Ext.get(this.getEl()),{
msg : '数据加载中...',
removeMask : true// 完成后移除
}); 
loadMask.show();
}
},
load : {
fn : function(me, node, records, successful, eOpts){
loadMask.hide();
}
}