having trouble using UIViewControllerAnimatedTransitioning with swift 3

Question

I'm trying to follow this tutorial on building a custom transition. Once I got to a custom to the part that involves UIViewControllerAnimatedTransitioning, I began having errors. (I"m still new to swift, so it's taken a lot of effort with nothing to show so far).

I keep getting 2 errors. 1 -

Cannot assign value of type 'CircleTransitionAnimator' to type 'CAAnimationDelegate?'

2 -

Method does not override any method from its superclass

I'm guessing that the issue is related to UIViewControllerAnimatedTransitioning

class CircleTransitionAnimator: NSObject, UIViewControllerAnimatedTransitioning {

func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
    return 0.5
}

weak var transitionContext: UIViewControllerContextTransitioning?

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

    self.transitionContext = transitionContext

    var containerView = transitionContext.containerView()
    var fromViewController = transitionContext.viewController(forKey: UITransitionContextFromViewControllerKey) as! ViewController
    var toViewController = transitionContext.viewController(forKey: UITransitionContextToViewControllerKey) as! ViewController
    var button = fromViewController.button

    containerView.addSubview(toViewController.view)

    var circleMaskPathInitial = UIBezierPath(ovalIn: (button?.frame)!)
    var extremePoint = CGPoint(x: (button?.center.x)! - 0, y: (button?.center.y)! - toViewController.view.bounds.height)
    var radius = sqrt((extremePoint.x*extremePoint.x) + (extremePoint.y*extremePoint.y))
    var circleMaskPathFinal = UIBezierPath(ovalIn: (button?.frame)!.insetBy(dx: -radius, dy: -radius))

    var maskLayer = CAShapeLayer()
    maskLayer.path = circleMaskPathFinal.cgPath
    toViewController.view.layer.mask = maskLayer

    var maskLayerAnimation = CABasicAnimation(keyPath: "path")
    maskLayerAnimation.fromValue = circleMaskPathInitial.cgPath
    maskLayerAnimation.toValue = circleMaskPathFinal.cgPath
    maskLayerAnimation.duration = self.transitionDuration(using: transitionContext)
    maskLayerAnimation.delegate = self
    maskLayer.add(maskLayerAnimation, forKey: "path")


}

override func animationDidStop(anim: CAAnimation!, finished flag: Bool) {
    self.transitionContext?.completeTransition(!self.transitionContext!.transitionWasCancelled())
    self.transitionContext?.viewController(forKey: UITransitionContextFromViewControllerKey)?.view.layer.mask = nil
}

}

Answer 1

iOS 10 moves animationDidStart and animationDidStop to a formal CAAnimationDelegate protocol. Like beyowulf says, make the class conform to the delegate and remove the override tag from the method.