Swift - How to detect orientation changes

Swift 3 Above code updated:

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
    super.viewWillTransition(to: size, with: coordinator)

    if UIDevice.current.orientation.isLandscape {
        print("Landscape")
    } else {
        print("Portrait")
    }
}

Using NotificationCenter and UIDevice's beginGeneratingDeviceOrientationNotifications

Swift 4.2+

override func viewDidLoad() {
    super.viewDidLoad()        

    NotificationCenter.default.addObserver(self, selector: #selector(ViewController.rotated), name: UIDevice.orientationDidChangeNotification, object: nil)
}

deinit {
   NotificationCenter.default.removeObserver(self, name: UIDevice.orientationDidChangeNotification, object: nil)         
}

func rotated() {
    if UIDevice.current.orientation.isLandscape {
        print("Landscape")
    } else {
        print("Portrait")
    }
}

Swift 3

override func viewDidLoad() {
    super.viewDidLoad()        

    NotificationCenter.default.addObserver(self, selector: #selector(ViewController.rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
}

deinit {
     NotificationCenter.default.removeObserver(self)
}

func rotated() {
    if UIDevice.current.orientation.isLandscape {
        print("Landscape")
    } else {
        print("Portrait")
    }
}

let const = "Background" //image name
let const2 = "GreyBackground" // image name
    @IBOutlet weak var imageView: UIImageView!
    override func viewDidLoad() {
        super.viewDidLoad()

        imageView.image = UIImage(named: const)
        // Do any additional setup after loading the view.
    }

    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransition(to: size, with: coordinator)
        if UIDevice.current.orientation.isLandscape {
            print("Landscape")
            imageView.image = UIImage(named: const2)
        } else {
            print("Portrait")
            imageView.image = UIImage(named: const)
        }
    }