Swift UIView自定义转换在完成时捕捉回来

我已经实现了一个类

BubbleAnimator

，它应该在视图之间创建一个类似于气泡的转换，并通过

UIViewControllerTransitioningDelegate

-协议添加了它。到目前为止，演示动画效果很好（这就是为什么我没有为这一部分添加所有代码）

但是在关闭视图时，“fromViewController”会在动画的最后闪烁。在这个很短的闪烁之后，正确的

toViewController

再次显示，但是这个小故障非常恼人。 以下是相关的

animateTransition

-方法：

    //Get all the necessary views from the context
    let containerView = transitionContext.containerView()
    let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)
    let toViewController = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)

    //Presenting
    if self.reverse == false {

        //Add the destinationvc as subview
        containerView!.addSubview(fromViewController!.view)
        containerView!.addSubview(toViewController!.view)

        /*...Animating the layer goes here... */

    //Dismissing
    } else {
        containerView!.addSubview(toViewController!.view)
        containerView!.addSubview(fromViewController!.view)

        //Init the paths
        let circleMaskPathInitial = UIBezierPath(ovalInRect: self.originFrame)
        let extremePoint = CGPoint(x: originFrame.origin.x , y: originFrame.origin.y - CGRectGetHeight(toViewController!.view.bounds) )
        let radius = sqrt((extremePoint.x*extremePoint.x) + (extremePoint.y*extremePoint.y))
        let circleMaskPathFinal = UIBezierPath(ovalInRect: CGRectInset(originFrame, -radius, -radius))

        //Create a layer
        let maskLayer = CAShapeLayer()
        maskLayer.path = circleMaskPathFinal.CGPath
        fromViewController!.view.layer.mask = maskLayer


        //Create and add the animation
        let animation = CABasicAnimation(keyPath: "path")
        animation.toValue = circleMaskPathInitial.CGPath
        animation.fromValue = circleMaskPathFinal.CGPath
        animation.duration = self.transitionDuration(transitionContext)
        animation.delegate = self
        maskLayer.addAnimation(animation, forKey: "path")
    }

清理在委托方法中进行：

override public func animationDidStop(anim: CAAnimation, finished flag: Bool) {
    self.transitionContext?.completeTransition(!(self.transitionContext?.transitionWasCancelled())!)
}

我想，我在将视图添加到containerView时犯了一些错误，但我无法理解。另一种可能性是，当调用函数

completeTransition

时，视图的层掩码被重置。

多亏了我终于能够解决这个问题。简要说明：

CAAnimation仅操作视图的表示层，但不更改模型层。动画现在完成后，其值将捕捉回模型层的原始值和未更改的值

简短而简单的解决方法：

        animation.fillMode = kCAFillModeForwards
        animation.removedOnCompletion = false

更好的解决方案是在动画开始之前手动设置层位置的最终值，因为它不会阻止动画被删除。这样，将为模型图层指定正确的值：

        maskLayer.path = circleMaskPathInitial.CGPath
        //Create and add the animation below..