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有关设置手势识别器等交互式过渡的样板，请参阅此答案。

我正在尝试交互式转换，并花了很多时间试图弄清楚为什么控制器会正常转换而不是根据手势擦洗。我发现它不起作用，因为我使用的是UIViewPropertyAnimator. 切换到较旧的 UIView 动画块可以开箱即用。为什么？执行上有什么区别？

func animateTransition(using transitionContext: UIViewControllerContextTransitioning)
{
    // Ignore the forced unwrapping, for sake of brevity.
    let view_From       = transitionContext.viewController(forKey: .from)!.view!
    let view_To         = transitionContext.viewController(forKey: .to)!.view!
    transitionContext.containerView.insertSubview(view_To, aboveSubview: view_From)

    view_To.alpha = 0

    // This animation block works - it will follow the progress value of the interaction controller
    UIView.animate(withDuration: 1, animations: {
        view_From.alpha = 0.0
        view_To.alpha = 1.0
    }, completion: { finished in
        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    })

    // This animation block fails - it will play out normally and not be interactive
    /*
    let animator = UIViewPropertyAnimator(duration: 1, curve: .linear)
    animator.addAnimations {
        view_To.alpha = 1
        view_From.alpha = 0
    }
    animator.addCompletion { (position) in
        switch position {
        case .end: print("Completion handler called at end of animation")
        case .current: print("Completion handler called mid-way through animation")
        case .start: print("Completion handler called  at start of animation")
        }
        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    }
    animator.startAnimation()
    */
}
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1 回答 1

24

随着UIViewPropertyAnimatoriOS 10 的引入，该UIViewControllerAnimatedTransitioning协议也得到了更新。他们添加了一个func interruptibleAnimator(using: UIViewControllerContextTransitioning)您不必实现的可选选项（我猜是为了向后兼容）。但它是为您在此处提到的用例而添加的：利用新的UIViewPropertyAnimator.

所以要得到你想要的：首先，你必须实现interruptibleAnimator(using:)创建动画师 - 你不要在animateTransition(using:).

根据UIViewControllerAnimatedTransitioning（重点是我的）源代码中的评论（我不知道为什么文档不包含此信息）：

如果符合条件的对象创建的转换可以被中断，则它会实现此方法。例如，它可以返回 UIViewPropertyAnimator 的实例。预计此方法将在转换的生命周期内返回相同的实例。

您必须在过渡期间返回相同的动画师。这就是为什么你会发现

private var animatorForCurrentSession: UIViewImplicitlyAnimating?

我的BackAnimator实现中的属性 - 如果过渡尚未结束，我将当前动画师存储在那里以返回它。

实现时interruptibleAnimator(using:)，环境将采用该动画师并使用它，而不是使用animateTransition(using:). 但是为了保持协议的约定，animateTransition(using:)应该能够为过渡设置动画 - 但您可以简单地使用interruptibleAnimator(using:)创建动画师并在那里运行动画。

以下是一个工作BackAnimator实现，您可以将其与您在此 SO question中提到的示例一起使用。我使用你的代码作为基础，但你可以简单地将我的代码换成BackAnimator他们的实现，你就可以开始了（我正在他们的例子中测试它）。

class BackAnimator : NSObject, UIViewControllerAnimatedTransitioning {
    // property for keeping the animator for current ongoing transition
    private var animatorForCurrentTransition: UIViewImplicitlyAnimating?

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

    func interruptibleAnimator(using transitionContext: UIViewControllerContextTransitioning) -> UIViewImplicitlyAnimating {
        // as per documentation, the same object should be returned for the ongoing transition
        if let animatorForCurrentSession = animatorForCurrentTransition {
            return animatorForCurrentSession
        }
        // normal creation of the propertyAnimator
        let view_From       = transitionContext.viewController(forKey: .from)!.view!
        let view_To         = transitionContext.viewController(forKey: .to)!.view!
        transitionContext.containerView.insertSubview(view_To, aboveSubview: view_From)

        view_To.alpha = 0
        let animator = UIViewPropertyAnimator(duration: transitionDuration(using: transitionContext), curve: .linear)
        animator.addAnimations {
            view_To.alpha = 1
            view_From.alpha = 0
        }
        animator.addCompletion { (position) in
            switch position {
            case .end: print("Completion handler called at end of animation")
            case .current: print("Completion handler called mid-way through animation")
            case .start: print("Completion handler called  at start of animation")
            }
            // transition completed, reset the current animator:
            self.animatorForCurrentTransition = nil

            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        // keep the reference to current animator
        self.animatorForCurrentTransition = animator
        return animator
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        // animateTransition should work too, so let's just use the interruptibleAnimator implementation to achieve it
        let anim = self.interruptibleAnimator(using: transitionContext)
        anim.startAnimation()
    }
}

另请注意，由我们返回的动画interruptibleAnimator(using:)器不是由我们启动的——环境会在适当的时候启动它。

PS：我对这个主题的大部分知识都来自于尝试实现一个开源容器，该容器将允许其容器之间的自定义交互式转换 - InteractiveTransitioningContainer。也许你也会从中找到一些灵感:)。

于 2018-01-04T07:36:21.927 回答