ios - UIViewControllerAnimatedTransitioning 无法正常工作

Question

我想在navigationController的推送和弹出上制作一个过渡动画。但它的工作原理真的很奇怪。就像 1/5 倍一样，fromViewController 会淡出，但 toViewController 不会淡入，它只是出现。限制有时也会变得很奇怪。如果我使用标准过渡，那就没问题了。这是我的过渡类(class):

class TMFadeAnimator: NSObject, UIViewControllerAnimatedTransitioning {

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.5
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {

        let toViewController   = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)
        let fromViewController   = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)
        toViewController?.beginAppearanceTransition(true, animated: true)
        fromViewController?.beginAppearanceTransition(false, animated: true)

        transitionContext.containerView()!.addSubview(toViewController!.view)


        toViewController!.view.alpha = 0.0

        UIView.animateWithDuration(self.transitionDuration(transitionContext), animations: {
            toViewController!.view.alpha = 1.0
            fromViewController!.view.alpha = 0.0
        }) { (finished) in
            toViewController?.endAppearanceTransition()
            fromViewController?.endAppearanceTransition()
            transitionContext.completeTransition(finished)
        }
    }
}

Answer 1

奇怪的是，通过将 toViewController?.view.frame = fromViewController!.view.frame 放在 toViewController 和 fromViewController 后面就解决了问题> 被定义。 (感谢 A'sa Dickens 的发现)。这是最终的代码

class TMFadeAnimator: NSObject, UIViewControllerAnimatedTransitioning {

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.5
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {

        let toViewController   = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)
        let fromViewController   = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)

        toViewController?.view.frame = fromViewController!.view.frame

        toViewController?.beginAppearanceTransition(true, animated: true)
        fromViewController?.beginAppearanceTransition(false, animated: true)

        transitionContext.containerView()!.addSubview(toViewController!.view)


        toViewController!.view.alpha = 0.0

        UIView.animateWithDuration(self.transitionDuration(transitionContext), animations: {
            toViewController!.view.alpha = 1.0
            fromViewController!.view.alpha = 0.0
        }) { (finished) in
            toViewController?.endAppearanceTransition()
            fromViewController?.endAppearanceTransition()
            transitionContext.completeTransition(finished)
        }
    }
}