动画在自定义动画过渡视图控制器中无法顺利完成

Question

我正在尝试为新的视图控制器实现自定义动画。第一部动画效果很好，但第二部动画并不顺畅。我在过去2个小时内玩过代码，但仍无法弄清楚。该类使用UIViewControllerAnimatedTransitioning协议。

这是一段视频，向您展示它的外观 https://www.youtube.com/watch?v=kEDXpk3HMe0

你会在最后看到它只是跳到屏幕的整个尺寸。

扩展名CustomPresentedViewController：UIViewControllerTransitioningDelegate {

func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return CustomModalShowAnimator()
}


func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return nil
}

}

class CustomModalShowAnimator: NSObject, UIViewControllerAnimatedTransitioning {

func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
    return 2
}


func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {


    guard let toViewController =  transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) else { return }

    let transitionContainer = transitionContext.containerView


    var transform = CGAffineTransform.identity
    transform = transform.concatenating(CGAffineTransform(scaleX: 45, y: 0))

    toViewController.view.transform = transform
    toViewController.view.alpha = 0


    transitionContainer.addSubview(toViewController.view)

    let animationTiming = UISpringTimingParameters(dampingRatio: 1, initialVelocity: CGVector(dx: 5, dy: 0))

    let animator = UIViewPropertyAnimator(duration: transitionDuration(using: transitionContext), timingParameters: animationTiming)

    animator.addAnimations {
        toViewController.view.transform = CGAffineTransform.identity
        toViewController.view.alpha = 1
    }

    animator.addCompletion { finished in
        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    }

    animator.startAnimation()
}

}