flex树默认打开所有节点的写法
参考：http://www.iteye.com/topic/441725

当xml是写在mxml中时，可以在页面的 creationComplete="init()"里直接写

protected function showTreeResult_resultHandler(event:ResultEvent):void{var xmlStr:String = event.result as String;treeData = new XML(xmlStr);tree.callLater(expandTree);}private function expandTree():void{tree.expandChildrenOf(treeData,true);}