fade between two UIButton images

Question

i want to fade between two UIButton images for the purpose of setting favorites in a UITableView.

Currently the transition is done without effect - it just changes t

Answer 1

@SuperDuperTango's answer in Swift 4.2:

extension UIButton {
    func changeImageAnimated(image: UIImage?) {
        guard let imageView = self.imageView, let currentImage = imageView.image, let newImage = image else { return }

        CATransaction.begin()
        CATransaction.setCompletionBlock {
            self.setImage(newImage, for: .normal)
        }
        let crossFade: CABasicAnimation = CABasicAnimation(keyPath: "contents")
        crossFade.duration = 0.3
        crossFade.fromValue = currentImage.cgImage
        crossFade.toValue = newImage.cgImage
        crossFade.isRemovedOnCompletion = false
        crossFade.fillMode = CAMediaTimingFillMode.forwards
        imageView.layer.add(crossFade, forKey: "animateContents")
        CATransaction.commit()
    }
}

Answer 2

jkanter answer in Swift:

let crossFade = CABasicAnimation.init(keyPath: "contents")
crossFade.duration = 0.7
crossFade.fromValue = oldImage.cgImage
crossFade.toValue = newImage.cgImage
crossFade.isRemovedOnCompletion = false
crossFade.fillMode = kCAFillModeForwards
button.imageView?.layer.add(crossFade, forKey: "animateContents")

//Make sure to add Image normally after so when the animation
//is done it is set to the new Image
button.setImage(newImage, for: .normal)