Your method isn't getting called at all because you have the wrong signature. It was changed in Xcode 8 beta 6 to:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
Note that the type of sender is Any? instead of AnyObject?. You should have had an error after upgrading Xcode which told you your method wasn't overriding any method from its superclass which should have clued you in before you deleted the override.
