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

This is a slight improvement to @Ponja's answer that generally works well. Unfortunately, the newImage doesn't "stick", so if you wanted to toggle between two images, the first fade would work smoothly, but going back to the original image would "snap" back with no fade. Fixed it by using a CATransaction:

import UIKit

extension UIButton {
    func changeImageAnimated(image: UIImage?) {
        guard let imageView = self.imageView, currentImage = imageView.image, newImage = image else {
            return
        }
        CATransaction.begin()
        CATransaction.setCompletionBlock {
            self.setImage(newImage, forState: UIControlState.Normal)
        }
        let crossFade: CABasicAnimation = CABasicAnimation(keyPath: "contents")
        crossFade.duration = 0.3
        crossFade.fromValue = currentImage.CGImage
        crossFade.toValue = newImage.CGImage
        crossFade.removedOnCompletion = false
        crossFade.fillMode = kCAFillModeForwards
        imageView.layer.addAnimation(crossFade, forKey: "animateContents")
        CATransaction.commit()
    }
}