UIScrollView 上的“CALayer 位置包含 NaN：[nan nan]”

Question

我正在开发一个屏幕，它在UIScrollView 内只有一个UIImageView。 UIScrollView 使用户能够固定和缩放图像。我从下面的帖子中得到了帮助。它使用故事板和自动布局。基本上，它有 8 个约束，分别是顶部、底部、前导和尾随（scrollview 到 superview 和 imageView 到 scrollView）。示例帖子在情节提要中设置图像，因此不需要指定任何特定的高度或宽度。

https://www.raywenderlich.com/560-uiscrollview-tutorial-getting-started

我的问题是，当我使用相同的代码但以编程方式执行所有操作时，我可以看到图像（已放大），我可以用一根手指滚动，但当我想捏它时（缩小、放大）我得到了

'CALayer 位置包含 NaN: [nan nan]'

错误。我认为这是因为滚动视图没有设置 contentSize 或 contentOffset 但无论我设置该属性，我都得到了同样的错误。

 override func viewDidLoad() {

    self.scrollView.delegate = self
    self.scrollView.translatesAutoresizingMaskIntoConstraints = false
    self.imageView.translatesAutoresizingMaskIntoConstraints = false
    imageView.image = photo
    imageView.contentMode = .scaleAspectFit
    scrollView.addSubview(imageView)
    self.view.addSubview(scrollView)
    self.imageView.setContentHuggingPriority(UILayoutPriority.init(251), for: NSLayoutConstraint.Axis.vertical)
    self.imageView.setContentHuggingPriority(UILayoutPriority.init(251), for: NSLayoutConstraint.Axis.horizontal)

    scrollView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
    scrollView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
    scrollView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
    scrollView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true

    imageViewTopConstraint = imageView.topAnchor.constraint(equalTo: self.scrollView.topAnchor, constant: 0)
    imageViewTopConstraint.isActive = true

    imageViewBottomConstraint = imageView.bottomAnchor.constraint(equalTo: self.scrollView.bottomAnchor, constant: 0)
    imageViewBottomConstraint.isActive = true

    imageViewLeadingConstraint = imageView.leadingAnchor.constraint(equalTo: self.scrollView.leadingAnchor, constant: 0)
    imageViewLeadingConstraint.isActive = true

    imageViewTrailingConstraint = imageView.trailingAnchor.constraint(equalTo: self.scrollView.trailingAnchor, constant: 0)
    imageViewTrailingConstraint.isActive = true

    scrollView.contentSize = imageView.bounds.size

}

fileprivate func updateMinZoomScaleForSize(_ size: CGSize) {
    let widthScale = size.width / imageView.bounds.width
    let heightScale = size.height / imageView.bounds.height
    let minScale = min(widthScale, heightScale)

    scrollView.minimumZoomScale = minScale

    scrollView.zoomScale = minScale
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    updateMinZoomScaleForSize(view.bounds.size)
}

fileprivate func updateConstraintsForSize(_ size: CGSize) {

    let yOffset = max(0, (size.height - imageView.frame.height) / 2)
    imageViewTopConstraint.constant = yOffset
    imageViewBottomConstraint.constant = yOffset

    let xOffset = max(0, (size.width - imageView.frame.width) / 2)
    imageViewLeadingConstraint.constant = xOffset
    imageViewTrailingConstraint.constant = xOffset

    view.layoutIfNeeded()
}

}

extension ZoomedPhotoViewController: UIScrollViewDelegate {
func viewForZooming(in scrollView: UIScrollView) -> UIView? {
    return imageView
}

func scrollViewDidZoom(_ scrollView: UIScrollView) {
    updateConstraintsForSize(view.bounds.size)
}

}

Answer 1

我通过将 updateMinZoomScaleForSize(view.bounds.size) 函数从 ViewDidLayoutSubViews() 移动到 ViewDidLoad() 并在调用 ZoomScale 函数之前调用 self.view.layoutIfNeeded() 来使其工作。因此我的最终和工作ViewDidLoad()

    override func viewDidLoad() {
    super.viewDidLoad()
    self.scrollView.delegate = self
    self.scrollView.translatesAutoresizingMaskIntoConstraints = false
    self.imageView.translatesAutoresizingMaskIntoConstraints = false
    imageView.image = photo
    imageView.contentMode = .scaleAspectFit
    imageView.clipsToBounds = true
    scrollView.addSubview(imageView)
    //scrollView.contentSize = CGSize(width: imageView.image!.size.width, height: imageView.image!.size.height)
    self.view.addSubview(scrollView)
    self.imageView.setContentHuggingPriority(UILayoutPriority.init(251), for: NSLayoutConstraint.Axis.vertical)
   self.imageView.setContentHuggingPriority(UILayoutPriority.init(251), for: NSLayoutConstraint.Axis.horizontal)

    scrollView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
    scrollView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
    scrollView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
    scrollView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true

    imageViewTopConstraint = imageView.topAnchor.constraint(equalTo: self.scrollView.topAnchor, constant: 0)
    imageViewTopConstraint.isActive = true

    imageViewBottomConstraint = imageView.bottomAnchor.constraint(equalTo: self.scrollView.bottomAnchor, constant: 0)
    imageViewBottomConstraint.isActive = true

    imageViewLeadingConstraint = imageView.leadingAnchor.constraint(equalTo: self.scrollView.leadingAnchor, constant: 0)
    imageViewLeadingConstraint.isActive = true

    imageViewTrailingConstraint = imageView.trailingAnchor.constraint(equalTo: self.scrollView.trailingAnchor, constant: 0)
    imageViewTrailingConstraint.isActive = true


    self.view.layoutIfNeeded()
    updateMinZoomScaleForSize(view.bounds.size)

}