ios - 执行 UIViewControllerAnimatedTransitioning 时隐藏快照 View

Question

我试图在推送 UIViewController 时进行简单的动画转换，但似乎我遗漏了一些东西。

我将 subview 的快照从 fromViewController 动画化到 toViewController。我正在为快照的帧设置动画，但快照在整个动画过程中都是不可见的。

这是一个简单的代码示例。我正在尝试将单个 UILabel 从第一个 Controller 动画化到第二个 Controller 。我特别想为从 toViewConroller 而不是 fromViewController 拍摄的快照制作动画。

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    let fromVC = transitionContext.viewController(forKey: .from) as! ViewController
    let toVC   = transitionContext.viewController(forKey: .to)   as! SecondViewController

    let container = transitionContext.containerView

    toVC.view.frame = fromVC.view.frame
    container.addSubview(toVC.view)
    toVC.view.layoutIfNeeded()

    let animatedFromView = fromVC.label!
    let animatedToView = toVC.label!

    let initialFrame = container.convert(animatedFromView.frame,
                                         from: animatedFromView.superview)
    let finalFame = container.convert(animatedToView.frame,
                                      to: animatedToView.superview)

    let snapshot = animatedToView.snapshotView(afterScreenUpdates: true)!
    snapshot.frame = initialFrame

    container.addSubview(snapshot)

    animatedFromView.alpha = 0
    animatedToView.alpha = 0

    UIView.animate(withDuration: 2,
                   animations: {
                    snapshot.frame = finalFame

    }) { (_) in
        snapshot.removeFromSuperview()

        fromVC.label.alpha = 1
        toVC.label.alpha = 1

        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    }
}

我猜快照是隐藏的，因为将 animatedToView 的 alpha 设置为 0，但是我不确定如何在不设置它的情况下实现该动画。

Answer 1

我试过你的代码，它工作正常。我改变了一些东西，比如对初始帧进行硬编码，这样我就可以看到效果，也可以从 viewController alpha 看到效果。

::::::用于呈现 View Controller

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    let fromVC = transitionContext.viewController(forKey: .from) as! ViewController
    let toVC   = transitionContext.viewController(forKey: .to)   as! SecondViewController

    let container = transitionContext.containerView

    toVC.view.frame = fromVC.view.frame
    container.addSubview(toVC.view)
    toVC.view.layoutIfNeeded()

    let animatedFromView = fromVC.view!
    let animatedToView = toVC.view!

    let initialFrame = container.convert(CGRect(x: 0, y: 200, width: 100, height: 100),
                                         from: animatedFromView.superview)
    let finalFame = container.convert(animatedToView.frame,
                                      to: animatedToView.superview)

    let snapshot = animatedToView.snapshotView(afterScreenUpdates: true)!
    snapshot.frame = initialFrame

    container.addSubview(snapshot)

    animatedFromView.alpha = 1
    animatedToView.alpha = 0

    UIView.animate(withDuration: 2,
                   animations: {
                    snapshot.frame = finalFame

    }) { (_) in
        snapshot.removeFromSuperview()

        fromVC.view.alpha = 1
        toVC.view.alpha = 1

        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    }
}

::::::::::::::::::在推送 View Controller 时使用

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

    guard let fromView = transitionContext.view(forKey: UITransitionContextViewKey.from) else { return }
    guard let toView = transitionContext.view(forKey: UITransitionContextViewKey.to) else { return }

    let container = transitionContext.containerView

    container.insertSubview(toView, belowSubview: fromView)

    let animatedFromView = fromView
    let animatedToView = toView

    let initialFrame = container.convert(CGRect(x: 0, y: 200, width: 100, height: 100),
                                         from: animatedFromView.superview)

    let finalFame = container.convert(animatedToView.frame,
                                      to: animatedToView.superview)

    let snapshot = animatedToView.snapshotView(afterScreenUpdates: true)!
    snapshot.frame = initialFrame

    container.addSubview(snapshot)

    animatedFromView.alpha = 1
    animatedToView.alpha = 1

    UIView.animate(withDuration: 2,
                   animations: {
                    snapshot.frame = finalFame

    }) { (_) in
        snapshot.removeFromSuperview()

        //fromVC.view.alpha = 1
        //toVC.view.alpha = 1

        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    }
}