当 UIPercentDrivenInteractiveTransition 结束一半时在 Cancel 上触发动画

Question

如果交互结束并且动画被取消，强制自定义过渡返回到视图控制器的原始位置是否是一个好习惯。我有以下实现决定何时关闭平移手势上的视图控制器。如果平移手势提前结束，我希望在考虑持续时间与平移手势

上的progress值成正比之前，动画回到原始位置，就像它的呈现方式一样

protocol AnimationControllerDelegate: AnyObject {
  func shouldHandlePanelInteractionGesture() -> Bool
}

typealias PanGestureHandler = AnimationControllerDelegate & UIViewController & Animatable

final class CustomInteractionController: UIPercentDrivenInteractiveTransition, UIGestureRecognizerDelegate {
    var interactionInProgress: Bool = false
    private var shouldCompleteTransition: Bool = false
    private var startTransitionY: CGFloat = 0
    private var panGestureRecognizer: UIPanGestureRecognizer?
    private weak var viewController: PanGestureHandler?

    func wireToViewController(viewController: Any) {
        guard let viewControllerDelegate = viewController as? PanGestureHandler else {
            return
        }

        self.viewController = viewControllerDelegate

        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handlePanGestureRecognizer(_:)))

        panGestureRecognizer = panGesture
        panGestureRecognizer?.delegate  = self

        self.viewController?.view.addGestureRecognizer(panGesture)
    }

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer,
                           shouldRecognizeSimultaneouslyWith
        otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }

    @objc
    func handlePanGestureRecognizer(_ gestureRecognizer: UIPanGestureRecognizer) {
        guard let childView = gestureRecognizer.view,
            let parentView = childView.superview,
            let panGestureHandler = viewController else {
            return
        }

        switch gestureRecognizer.state {
        case .began:
            break
        case .changed:
            let translation = gestureRecognizer.translation(in: parentView)
            let velocity = gestureRecognizer.velocity(in: parentView)
            let state = gestureRecognizer.state

            if !panGestureHandler.shouldHandlePanelInteractionGesture() && percentComplete == 0 {
                return
            }

            let verticalMovement = translation.y / childView.bounds.height
            let downwardMovement = fmaxf(Float(verticalMovement), 0.0)
            let downwardMovementPercent = fminf(downwardMovement, 1.0)
            let progress = CGFloat(downwardMovementPercent)

            let alphaValue = (1 - progress) * 0.4

            panGestureHandler.shadowView.backgroundColor = Safety.Colors.backgroundViewColor(for: alphaValue)

            if abs(velocity.x) > abs(velocity.y) && state == .began {
                return
            }

            if !interactionInProgress {
                interactionInProgress = true
                startTransitionY = translation.y
                viewController?.dismiss(animated: true, completion: nil)
            } else {
                shouldCompleteTransition = progress > 0.3
                update(progress)
            }
        case .cancelled:
            interactionInProgress = false
            startTransitionY = 0
            cancel()
        case .ended:
            interactionInProgress = false
            startTransitionY = 0
            if !shouldCompleteTransition {
                // Can I call a custom transition here back to original position?
                cancel()
            } else {
                finish()
            }
        case .failed:
            interactionInProgress = false
            startTransitionY = 0
            cancel()
        default:
            break
        }
    }
}

Answer 1

Is it a good practice to force custom transition back to original position for a view controller if the interaction ends and animation is cancelled.

是的，我认为如果用户取消他们的手势，最好将其反转。但你不必“强迫”它。您完成转换，只需表明您是希望它完成还是反转。因此，如果您取消动画，它会自动反转并返回到它自动为您显示的位置。除了 cancel.

，您无需执行任何操作

当然，这假定在动画师的动画完成块中，您在 completeTransition 中指出它是否完成：

UIView.animate(withDuration: 0.25, animations: {
    ...
}, completion: { _ in
    transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
})

因此，如果没有取消，动画将完成。但如果取消它会反转。

就个人而言，在我的手势识别器中，我通常会执行以下操作：

如果state的手势是.began，我会：
- 实例化 UIPercentDrivenInteractiveTransition，UIViewControllerTransitioningDelegate 将 return 来自 interactionControllerForPresentation(using)；和
- 执行 present/dismiss UIPercentDrivenInteractiveTransition
当手势更新为.changed的state时，只是update UIPercentDrivenInteractiveTransition；和
完成后，您可以 finish 或 cancel 它。而cancel会自动触发反转动画

例如，我从左到右的“关闭”手势最终看起来像：

@objc func handleLeftToRightPan(_ gesture: UIPanGestureRecognizer) {
    let percent = (gesture.translation(in: gesture.view).x) / gesture.view!.bounds.width

    switch gesture.state {
    case .began:
        interactionController = UIPercentDrivenInteractiveTransition()
        dismiss(animated: true)
        interactionController?.update(percent)

    case .changed:
        interactionController?.update(percent)

    case .ended, .cancelled:
        let velocity = gesture.velocity(in: gesture.view).x
        if velocity > 0 || (velocity == 0 && percent > 0.5) {
            interactionController?.finish()
        } else {
            interactionController?.cancel()
        }
        interactionController = nil

    default:
        break
    }
}

就我个人而言，对于 finish 与 cancel 逻辑，我检查是否：

是手势方向的velocity（在从左到右的“解雇”手势中，这意味着我检查它是否是积极的x velocity) ...这意味着如果用户轻弹，即使是屏幕的一小部分，我仍然会认为这是一个完全过渡的意图；
只有当 velocity 为零时，我才会检查完成百分比（例如，如果他们走了 ¾，停下来，然后放手，我假设他们想要 finish 手势，但如果他们只走了 ¼ 路然后停下来放手，我假设他们打算取消手势。
不用说，如果他们反转手势的方向，我认为取消了他们完成转换的意图

但是如您所见，我除了 cancel 什么都没做，动画自动反转。所以，在这里我从第二个视图控制器开始解雇过渡，回到第一个，但是 cancel UIPercentDrivenInteractiveTransition （在这种情况下，通过反转手势的方向并放手）和我的动画师将在其完成处理程序中将适当的 Bool 值传递给其完成处理程序中的 completeTransition，它会自动返回动画，而我无需做任何工作：

当 UIPercentDrivenInteractiveTransition 结束一半时在 Cancel 上触发动画

Trigger animation on Cancel when UIPercentDrivenInteractiveTransition ends half

uiviewanimationtransition

ios