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