flex的dropdownlist在alert .show之后无法关闭下拉框的解决办法
参考：https://issues.apache.org/jira/browse/FLEX-20103

//E_list是s:DropDownListE_list.openDropDown();E_list.callLater(alert);private function alert():void{   Alert.show("Item(s) already used by another effect");}