CAKeyframeAnimation rotation don't draw real shadow - ios

Question

I want to rotate an UIImageView with CAKeyframeAnimation. The problem is that the shadow rotates with the object, making a non-real effect... The shadow must remain under the image, not rotating around it
This is my code. Very simple:
let imagen:UIImageView = UIImageView(image:UIImage(named: "material6.png"))
self.view.addSubview(imagen)
imagen.center = CGPoint(x: 100, y: 100)
imagen.layer.shadowOpacity = 0.75
imagen.layer.shadowOffset = CGSize(width: 0, height: 15)
//Animación del ángulo
let animacionAngulo = CAKeyframeAnimation(keyPath: "transform.rotation.z")
var valoresAngulo = [NSNumber]()
let degrees:Float = 360
let radians = degrees * Float.pi / Float(180.0)
valoresAngulo.append(NSNumber(value: 0))
valoresAngulo.append(NSNumber(value: radians))
animacionAngulo.values = valoresAngulo
//Permite añadir varias animaciones y gestionarlas a la vez
animacionAngulo.repeatCount = Float.infinity
animacionAngulo.duration = 2.0
imagen.layer.add(animacionAngulo, forKey: nil)
Any solution?

Answer 1

If the shadow is rotating along with the image. You can solve it by adding an UIView with same dimensions of your UIImageView below your UIImageView. If you add shadow to your UIView instead of UIImageView, you can achieve the desired effect in this case.
let imagen:UIImageView = UIImageView(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
imagen.center = CGPoint(x: 100, y: 100)
imagen.backgroundColor = UIColor.red
let belowView: UIView = UIView(frame: imagen.frame)
belowView.backgroundColor = UIColor.white
belowView.layer.shadowOpacity = 0.75
belowView.layer.shadowOffset = CGSize(width: 0, height: 15)
self.view.addSubview(belowView)
self.view.addSubview(imagen)
//Animación del ángulo
let animacionAngulo = CAKeyframeAnimation(keyPath: "transform.rotation.z")
var valoresAngulo = [NSNumber]()
let degrees:Float = 360
let radians = degrees * Float.pi / Float(180.0)
valoresAngulo.append(NSNumber(value: 0))
valoresAngulo.append(NSNumber(value: radians))
animacionAngulo.values = valoresAngulo
//Permite añadir varias animaciones y gestionarlas a la vez
animacionAngulo.repeatCount = Float.infinity
animacionAngulo.duration = 2.0
imagen.layer.add(animacionAngulo, forKey: nil)