How to make a button flash or blink?

Question

I am trying to change a button\'s color (just a flash/blink) to green when a scan is correct and red when there\'s a problem. I am able to do this with a view like so

Answer 1

Another smoothly animating version for Swift 5:

 public extension UIView {
  func blink(duration: TimeInterval) {
    let initialAlpha: CGFloat = 1
    let finalAlpha: CGFloat = 0.2
    
    alpha = initialAlpha
    
    UIView.animateKeyframes(withDuration: duration, delay: 0, options: .beginFromCurrentState) {
      UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 0.5) {
        self.alpha = finalAlpha
      }
      
      UIView.addKeyframe(withRelativeStartTime: 0.5, relativeDuration: 0.5) {
        self.alpha = initialAlpha
      }
    }
  }
}