UINavigationController 在转换到另一个 VC 时删除阴影答案

【问题标题】：UINavigationController remove drop shadow when transitioning to another VCUINavigationController 在转换到另一个 VC 时删除阴影
【发布时间】：2015-06-08 22:09:17
【问题描述】：

当使用UINavigationController 和pushViewController:animated: 将另一个视图控制器推入堆栈时，在转换过程中总是会显示一个阴影：

我有一个应用，其中导航控制器上有一个视频背景，所以我想删除那个阴影，因为它在转换过程中看起来很奇怪。

有什么办法可以彻底去除吗？（我不是在说UINavigationBarshadow）

【问题讨论】：

你解决了吗？
@BorisNikolić - 不。我最终使用了UIViewController，并在那里构建了所有动画。

标签： ios objective-c uiviewcontroller uinavigationcontroller

【解决方案1】：

解决方案：

// set one of viewcontrollers (usual first) as navigationController delegate

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationController?.delegate = self
    }

}

// make the view controller conform to `UINavigationControllerDelegate`

extension ViewController: UINavigationControllerDelegate {
    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return PushPopAnimator(operation: operation)
    }
}

// The animation controller

class PushPopAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    let operation: UINavigationControllerOperation

    init(operation: UINavigationControllerOperation) {
        self.operation = operation
        super.init()
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.25
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let from = transitionContext.viewController(forKey: .from)!
        let to   = transitionContext.viewController(forKey: .to)!

        let rightTransform = CGAffineTransform(translationX: transitionContext.containerView.bounds.size.width, y: 0)
        let leftTransform = CGAffineTransform(translationX: -transitionContext.containerView.bounds.size.width, y: 0)

        if operation == .push {
            to.view.transform = rightTransform
            transitionContext.containerView.addSubview(to.view)
            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: { 
                from.view.transform = leftTransform
                to.view.transform = .identity
            }, completion: { finished in
                from.view.transform = .identity
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        } else if operation == .pop {
            to.view.transform = leftTransform
            transitionContext.containerView.insertSubview(to.view, belowSubview: from.view)
            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                to.view.transform = .identity
                from.view.transform = rightTransform
            }, completion: { finished in
                from.view.transform = .identity
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        }
    }
}

【讨论】：

我知道这是一个 Swift 答案，但对于 Objective-C，键是 UITransitionContextFromViewControllerKey 和 UITransitionContextToViewControllerKey。不要将它们与UITransitionContextToViewKey/UITransitionContextToViewKey 混淆（注意缺少的Controller）。在过去的一个小时里，这让我发疯了。
此解决方案消除了通过滑动返回导航的可能性。