iOS - Transition between gradients?

Question

I'm trying to rotate the background colour endlessly between two different gradients, but the actual transition isn't lasting as long as expected (it lasts for less than a second and there's no delay between each transition).

var backgroundColours = [CAGradientLayer()]
var backgroundLoop = 0

override func viewDidLoad() {
    super.viewDidLoad()
    backgroundColours = [Colors.init().one, Colors.init().two] // These are two CAGradientLayers but I haven't included their code
    backgroundLoop = 0
    self.animateBackgroundColour()
}

func animateBackgroundColour () {

    backgroundLoop = (backgroundLoop + 1) % (backgroundColours.count)

    UIView.animate(withDuration: 2.0, delay: 2.0, options: .curveLinear, animations: {
        self.view.backgroundColor = UIColor.clear
        let backgroundLayer = self.backgroundColours[self.backgroundLoop]
        backgroundLayer.frame = self.view.frame
        self.view.layer.insertSublayer(backgroundLayer, at: 0)
    }, completion: { (Bool) -> Void in
        self.animateBackgroundColour()
    })

This is all inside the ViewController Class

Answer 1

UIView.animate animates only about five specialized view properties. You are not animating any of those properties. What you want is layer animation (e.g. CABasicAnimation).