All previous contributes are fine, but a little note:
a) if orientation is set in plist, only portrait or example, You will be not notified via viewWillTransition
b) if we anyway need to know if user has rotated device, (for example a game or similar..) we can only use:
NotificationCenter.default.addObserver(self, selector: #selector(ViewController.rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
tested on Xcode8, iOS11.