Tree的全部节点展开

大家都知道应该用expandChildrenOf(item,true)，但是Flex2说明中很明确写道:
"If you set dataProvider and then immediately call expandChildrenOf() you may not see the correct behavior. You should either wait for the component to validate or call the validateNow() method. "

 

treePlayList.dataProvider = results;
// 刷新 非常必要
treePlayList.validateNow();
// 全部展开
treePlayList.selectedIndex = 0 ;
treePlayList.expandChildrenOf(treePlayList.selectedItem, true );