iOS 7 UINavigationController 推送动画阴影

Swift
extension YourNavigationController: UINavigationControllerDelegate {
    
    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationController.Operation, from fromViewController: UIViewController, to toViewController: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        
        if operation == .push {
            return PushAnimationController()
        }
        
        return nil
    }
}
class PushAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let toView = transitionContext.view(forKey: .to) else { return }
        
        let contAInerView = transitionContext.contAInerView
        contAInerView.addSubview(toView)
        
        toView.layer.shadowColor = UIColor.black.cgColor
        toView.layer.shadowOpacity = 0.5
        toView.layer.shadowOffset = CGSize(width: 0, height: 2)
        toView.layer.shadowRadius = 3
        
        // 添加其他推送动画代码
        
        UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
            // 设置推送动画效果
        }) { (_) in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
}