CustomTransition.swift

final class CustomTransition: NSObject, CAAnimationDelegate, UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 1.0
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let toViewController = transitionContext.viewController(forKey: .to) else { return }
        transitionContext.containerView.addSubview(toViewController.view)
        
        if transitionContext.isAnimated {
            toViewController.view.frame = transitionContext.finalFrame(for: toViewController)
            
            let opacity: CABasicAnimation = {
                let animation = CABasicAnimation(keyPath: "opacity")
                animation.duration = transitionDuration(using: transitionContext)
                animation.fromValue = 0.0
                animation.timingFunction = CAMediaTimingFunction(name: .easeIn)
                animation.toValue = 1.0
                return animation
            }()
            let rotation: CABasicAnimation = {
                let animation = CABasicAnimation(keyPath: "transform.rotation")
                animation.duration = transitionDuration(using: transitionContext)
                animation.fromValue = 0.0
                animation.toValue = 2.0 * 2.0 * Double.pi
                animation.timingFunction = CAMediaTimingFunction(name: .easeIn)
                return animation
            }()
            let scale: CABasicAnimation = {
                let animation = CABasicAnimation(keyPath: "transform.scale")
                animation.duration = transitionDuration(using: transitionContext)
                animation.fromValue = 0.1
                animation.toValue = 1.0
                animation.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
                return animation
            }()
            let group: CAAnimationGroup = {
                let group = CAAnimationGroup()
                group.animations = [opacity, rotation, scale]
                group.delegate = self
                group.duration = transitionDuration(using: transitionContext)
                return group
            }()
            self.transitionContext = transitionContext
            toViewController.view.layer.add(group, forKey: "rotateScaleGroup")
        }
        else {
            toViewController.view.frame = transitionContext.finalFrame(for: toViewController)
            transitionContext.completeTransition(true)
        }
    }
    
    private var transitionContext: UIViewControllerContextTransitioning? = nil
    
    func animationDidStop(_ animation: CAAnimation, finished isFinished: Bool) {
        transitionContext?.completeTransition(isFinished)
        transitionContext = nil
    }
}