ios - UIViewController 交互式转换 - 当交互式关闭被取消时，呈现的 View 消失

Question

我有一个演示应用程序，我试图在其中模仿邮件应用程序的“新消息”交互过渡 - 您可以向下拖动以关闭，但如果您拖得不够远， View 会弹回并且过渡是取消。我能够在我的演示应用程序中复制过渡和交互性，但我注意到当关闭过渡被取消时，呈现的 View Controller 动画回到原位，然后消失。这是它的样子:

我最好的猜测是过渡上下文的容器 View 由于某种原因被删除了，因为我向它添加了呈现的 View Controller 的 View 。以下是 UIViewControllerAnimatedTransitioning 对象中的演示和关闭代码:

显示过渡

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    guard let fromVC = transitionContext.viewController(forKey: .from),
        let toVC = transitionContext.viewController(forKey: .to)
        else {
            return
    }

    let containerView = transitionContext.containerView
    let finalFrame = transitionContext.finalFrame(for: toVC)
    let duration = transitionDuration(using: transitionContext)
    let topSafeAreaSpace = fromVC.view.safeAreaInsets.top // using fromVC safe area since it's on screen and has correct insets
    let topGap: CGFloat = topSafeAreaSpace + 20

    containerView.addSubview(toVC.view)

    toVC.view.frame = CGRect(x: 0,
                             y: containerView.frame.height,
                             width: toVC.view.frame.width,
                             height: toVC.view.frame.height - 30)

    UIView.animate(withDuration: duration, animations: {
        toVC.view.frame = CGRect(x: finalFrame.minX,
                                 y: finalFrame.minY + topGap,
                                 width: finalFrame.width,
                                 height: finalFrame.height - topGap)

        let sideGap: CGFloat = 20
        fromVC.view.frame = CGRect(x: sideGap,
                                   y: topSafeAreaSpace,
                                   width: fromVC.view.frame.width - 2 * sideGap,
                                   height: fromVC.view.frame.height - 2 * topSafeAreaSpace)
        fromVC.view.layer.cornerRadius = 10
        fromVC.view.layoutIfNeeded()
    }) { _ in
        transitionContext.completeTransition(true)
    }
}

关闭过渡

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    guard let fromVC = transitionContext.viewController(forKey: .from),
        let toVC = transitionContext.viewController(forKey: .to)
        else {
            return
    }

    let finalFrame = transitionContext.finalFrame(for: toVC)
    let duration = transitionDuration(using: transitionContext)

    UIView.animate(withDuration: duration, animations: {
        toVC.view.frame = finalFrame
        fromVC.view.frame = CGRect(x: fromVC.view.frame.minX,
                                   y: finalFrame.height,
                                   width: fromVC.view.frame.width,
                                   height: fromVC.view.frame.height)

        toVC.view.layer.cornerRadius = 0

        toVC.view.layoutIfNeeded()
    }) { _ in
        transitionContext.completeTransition(true)
    }
}

下面是 UIPercentDrivenInteractiveTransition 对象中的代码:

func handleGesture(_ gesture: UIPanGestureRecognizer) {
    #warning("need to use superview?")
    let translation = gesture.translation(in: gesture.view)
    var progress = translation.y / 400
    progress = min(1, max(0, progress)) // constraining value between 1 and 0

    switch gesture.state {
    case .began:
        interactionInProgress = true
        viewController.dismiss(animated: true, completion: nil)
    case .changed:
        shouldCompleteTransition = progress > 0.5
        update(progress)
    case .cancelled:
        interactionInProgress = false
        cancel()
    case .ended:
        interactionInProgress = false
        if shouldCompleteTransition {
            finish()
        } else {
            cancel()
        }
    default:
        break
    }
}

如有任何帮助，我们将不胜感激。值得注意的是，我使用了这个 Ray Wenderlich 教程作为引用 - https://www.raywenderlich.com/322-custom-uiviewcontroller-transitions-getting-started但是，在他们使用图像快照为过渡设置动画的地方，我使用的是 View Controller 的 View 。

Answer 1

感谢@Dare 的评论，我意识到所需要的只是对关闭动画完成 block 的一个小更新:

// before - broken

transitionContext.completeTransition(true)

// after - WORKING!

transitionContext.completeTransition(!transitionContext.transitionWasCancelled)