When Orientation is changed effects are not applied (swift3)

I am just trying to write code that only when the device is upside down will a label "dave" not be hidden. Right now the label "dave" is shown in all 4 orientations. This is my code.

import UIKit

class ViewController: UIViewController {

@IBOutlet var dave: UILabel!
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    s()

}


func s() {
    if UIDevice.current.orientation == UIDeviceOrientation.landscapeLeft {
        dave.isHidden = true




    } else if UIDevice.current.orientation == UIDeviceOrientation.landscapeRight {
        dave.isHidden = true


    } else if UIDevice.current.orientation == UIDeviceOrientation.portrait {
        dave.isHidden = true


    } else if UIDevice.current.orientation == UIDeviceOrientation.portraitUpsideDown {
        dave.isHidden = false
    }}}