ios - 呈现的 View Controller 在使用自定义 UIViewController 动画制作动画后消失

Question

我四处寻找这个问题的答案，并且在过去的两个小时里一直在绞尽脑汁。

我正在实现一个非常基本的自定义 View Controller 转换动画，它只是在呈现的 View Controller 上放大并在呈现的 View Controller 中增长。它添加了淡入淡出效果(0 到 1 alpha，反之亦然)。

它在呈现 View Controller 时工作正常，但在关闭时，它会将 presenting View Controller 带回原处以填满屏幕，但随后它莫名其妙地消失了。在这些动画之后我没有做任何改变 alpha 或隐藏值的事情，这几乎是一个新项目。我已经开发 iOS 应用程序 3 年了，所以我怀疑这可能是一个错误，除非有人能找出我哪里出错了。

class FadeAndGrowAnimationController : NSObject, UIViewControllerAnimatedTransitioning, UIViewControllerTransitioningDelegate {
func animationControllerForPresentedController(presented: UIViewController!, presentingController presenting: UIViewController!, sourceController source: UIViewController!) -> UIViewControllerAnimatedTransitioning! {
    return self
}

func animationControllerForDismissedController(dismissed: UIViewController!) -> UIViewControllerAnimatedTransitioning! {
    return self
}

func transitionDuration(transitionContext: UIViewControllerContextTransitioning!) -> NSTimeInterval {
    return 2
}

func animateTransition(transitionContext: UIViewControllerContextTransitioning!) {
    let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey) as UIViewController
    let toViewController = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey) as UIViewController

    toViewController.view.transform = CGAffineTransformMakeScale(0.5, 0.5)
    toViewController.view.alpha = 0

    transitionContext.containerView().addSubview(fromViewController.view)
    transitionContext.containerView().addSubview(toViewController.view)
    transitionContext.containerView().bringSubviewToFront(toViewController.view)

    UIView.animateWithDuration(self.transitionDuration(transitionContext), animations: {
        fromViewController.view.transform = CGAffineTransformScale(fromViewController.view.transform, 2, 2)
        fromViewController.view.alpha = 1

        toViewController.view.transform = CGAffineTransformMakeScale(1, 1)
        toViewController.view.alpha = 1
    }, completion: { finished in
        transitionContext.completeTransition(!transitionContext.transitionWasCancelled())
    })
}

以及要呈现的代码:

    let targetViewController = self.storyboard.instantiateViewControllerWithIdentifier("Level1ViewController") as Level1ViewController
    let td = FadeAndGrowAnimationController()

    targetViewController.transitioningDelegate = td
    targetViewController.modalPresentationStyle = .Custom

    self.presentViewController(targetViewController, animated: true, completion: nil)

如您所见，这是一个相当基本的动画。我在这里错过了什么吗？就像我说的，它呈现得非常好，然后完美地关闭 99.99%，但是在关闭之后下面的 View Controller 莫名其妙地被删除了。发生这种情况后，iPad 显示空白屏幕 - 全黑。

Answer 1

这似乎是一个 iOS8 错误。我找到了一个解决方案，但它是贫民窟。当一个 View 应该在屏幕上但不在屏幕上时，转换之后，需要像这样将它添加回窗口:

BOOL canceled = [transitionContext transitionWasCancelled];
[transitionContext completeTransition:!canceled];
if (!canceled)
    {
    [[UIApplication sharedApplication].keyWindow addSubview: toViewController.view];
    }

您可能需要考虑将哪个 View 添加回窗口，是否在取消或 !canceled 中执行，并且可能确保仅在关闭时执行，而不是在演示时执行。

来源:Container view disappearing on completeTransition: http://joystate.wordpress.com/2014/09/02/ios8-and-custom-uiviewcontrollers-transitions/