ios - 手动滚动由 UIViewPropertyAnimator 动画的 UIScrollView

Question

我有一个 UIScrollView它通过在 UIViewPropertyAnimator 内设置其内容偏移量来自动滚动.自动滚动按预期工作，但是我也希望能够中断动画以手动滚动。
此 seems to be one of the selling points的 UIViewPropertyAnimator :

...dynamically modify your animations before they finish

然而，它似乎不能很好地与 ScrollView 配合使用(除非我在这里做错了)。
在大多数情况下，它是有效的。当我在动画期间滚动时，它会暂停，然后在减速结束后恢复。然而，当我向底部滚动时，它就像已经在内容的末尾一样(即使它离它很远)。向顶部滚动时这不是问题。
注意到这一点后，我检查了 scrollView.contentOffset 的值。并且似乎卡在最大值+橡皮筋偏移处。我找到了 this question/answer这似乎表明这可能是 UIViewPropertyAnimator 的错误.
我的代码如下:

private var maxYOffset: CGFloat = .zero
private var interruptedFraction: CGFloat = .zero

override func layoutSubviews() {
    super.layoutSubviews()
    
    self.maxYOffset = self.scrollView.contentSize.height - self.scrollView.frame.height
}

private func scrollToEnd() {
    let maxOffset = CGPoint(x: .zero, y: self.maxYOffset)
    let duration = (Double(self.script.wordCount) / Double(self.viewModel.wordsPerMinute)) * 60.0
    
    let animator = UIViewPropertyAnimator(duration: duration, curve: .linear) {
        self.scrollView.contentOffset = maxOffset
    }
    animator.startAnimation()
    self.scrollAnimator = animator
}

extension UIAutoScrollView: UIScrollViewDelegate {

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        // A user initiated pan gesture will begin scrolling.
    
        if let scrollAnimator = self.scrollAnimator, self.viewModel.isScrolling {
            self.interruptedFraction = scrollAnimator.fractionComplete
            scrollAnimator.pauseAnimation()
        }
    }

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        if let scrollAnimator = self.scrollAnimator, self.viewModel.isScrolling {
            scrollAnimator.startAnimation()
        }
    }

    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        if let scrollAnimator = self.scrollAnimator, self.viewModel.isScrolling {
            scrollAnimator.startAnimation()
        }
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        switch scrollView.panGestureRecognizer.state {
        case .changed:
            // A user initiated pan gesture triggered scrolling.
                    
            if let scrollAnimator = self.scrollAnimator {
                let fraction = (scrollView.contentOffset.y - self.maxYOffset) / self.maxYOffset
                let boundedFraction = min(max(.zero, fraction), 1)
            
                scrollAnimator.fractionComplete = boundedFraction + self.interruptedFraction
            }
        default:
        break
        }
    }
}

有什么地方明显我出错了吗？或者我可以采用任何解决方法来使 ScrollView 在向下滚动时停止橡皮筋？

Answer 1

您可以添加点击手势识别器并调用此功能，

extension UIScrollView  {
    func stopDecelerating() {
        let contentOffset = self.contentOffset
        self.setContentOffset(contentOffset, animated: false)
    }
}