UIScrollView 在自动布局中未正确调整大小

Question

我正在尝试将 Ray Wenderlich UIScrollView Tutorial 的第 1 部分转换为使用通用设备的自动布局。我目前在导航控制器中嵌入了一个 UITableView，将 class ViewController 的 UIViewController 与 UIScrollView（无自定义 class）连接起来.导航控制器有一个不透明的导航栏，没有工具栏。 UIViewController 的属性可以在下面相册的第一张图片中看到。

Image Album

只有四个情节提要限制（如下所述），我的视图看起来像相册中的第二张图片，scrollView 的帧大小不正确 600x536。为了解决这个问题，我决定在运行时再次添加约束，在 viewDidLoad() in ViewController.swift 中。我现在总共有 8 个约束：

• 故事板上的 4 个约束条件：
  • scrollView.top = topLayoutGuide.bottom
  • scrollView.bottom = bottomLayoutGuide.top
  • scrollView.leading = superView.leading
  • scrollView.trailing = superView.trailing
• ViewController.swift 中的 4 个约束：
  • scrollView.top = topLayoutGuide
  • scrollView.bottom = view.bottom
  • scrollView.leading = view.leading
  • scrollView.trailing = view.trailing

由于这些限制，在缩放之前，我的视图现在看起来像第三张专辑图像，scrollView 的帧大小仍然不正确 375x667。缩放后，我的视图是正确的，看起来像第四张相册图像，scrollView 的帧大小正确 375x603。其他一些注意事项：

• self.topLayoutGuide.length = 0。不应该是64吗？ 20 个来自状态栏，44 个来自导航栏？
• 删除故事板约束会导致与没有编程约束相同的问题。为什么故事板约束仍然需要存在？
• 纯方法和混合方法我都试过了，都没有解决这个问题。
• 除了在故事板中禁用 Adjust Scroll View Insets、Extend Edges Under Top Bars 和 Extend Edges Under Opaque Bars（见第一张图片）外，我还在代码中禁用它们，但无济于事。
• 我无法使用插图，因为 UIScrollView 的框架在缩放后发生了变化。

如何让 UIScrollView 成为一个常数，合适的大小？

谢谢。

class ViewController: UIViewController, UIScrollViewDelegate

@IBOutlet var scrollView: UIScrollView!

var imageView: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()

    //Reset the layout
    scrollView.needsUpdateConstraints()
    scrollView.setNeedsLayout()
    scrollView.layoutIfNeeded()

    //Set storyboard settings just in case
    scrollView.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.extendedLayoutIncludesOpaqueBars = false
    self.edgesForExtendedLayout = .None
    self.automaticallyAdjustsScrollViewInsets = false
    self.navigationController?.navigationBar.translucent = false

    //Manually added constraints at runtime
    var constraintTS = NSLayoutConstraint(item: scrollView, attribute: .Top, relatedBy: .Equal, toItem: topLayoutGuide, attribute: .Bottom, multiplier: 1.0, constant: 0)
    var constraintBS = NSLayoutConstraint(item: scrollView, attribute: .Bottom, relatedBy: .Equal, toItem: view, attribute: .Bottom, multiplier: 1.0, constant: 0)
    var constraintLS = NSLayoutConstraint(item: scrollView, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .Leading, multiplier: 1.0, constant: 0)
    var constraintRS = NSLayoutConstraint(item: scrollView, attribute: .Trailing, relatedBy: .Equal, toItem: view, attribute: .Trailing, multiplier: 1.0, constant: 0)
    view.addConstraint(constraintTS)
    view.addConstraint(constraintBS)
    view.addConstraint(constraintLS)
    view.addConstraint(constraintRS)

    println(scrollView.frame.width)
    println(scrollView.frame.height)

    //Original Ray Wenderlich code
    let image1 = UIImage(named: "photo1")!
    imageView = UIImageView(image: image1)
    imageView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size: image1.size)
    scrollView.addSubview(imageView)
    scrollView.contentSize = image1.size

    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.height / scrollView.contentSize.height
    let minScale = min(scaleWidth, scaleHeight)
    scrollView.minimumZoomScale = minScale
    scrollView.maximumZoomScale = 1.0
    scrollView.zoomScale = minScale

    centerScrollViewContents()
}

func centerScrollViewContents() {
    let boundsSize = scrollView.bounds.size
    var contentsFrame =  imageView.frame

    if contentsFrame.size.width < boundsSize.width {
        contentsFrame.origin.x = (boundsSize.width - contentsFrame.width) / 2.0
    } else {
        contentsFrame.origin.x = 0.0
    }

    if contentsFrame.size.height < boundsSize.height {
        contentsFrame.origin.y = (boundsSize.height - contentsFrame.height) / 2.0
        println("boundsSize.height: \(boundsSize.height)")
        println("boundsSize.width:  \(boundsSize.width)")
        println("contentsFrame.origin.y: \(contentsFrame.origin.y)")
    } else {
        contentsFrame.origin.y = 0.0
    }

    imageView.frame = contentsFrame
}

func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
    return imageView
}

func scrollViewDidZoom(scrollView: UIScrollView) {
    centerScrollViewContents()
}

override func viewWillLayoutSubviews() {
    println(self.topLayoutGuide.length)
}

Answer 1

已解决！感谢 Working with Top Layout Guide in UIScrollView through Auto Layout。我认为 UIScrollView 不会使 topLayoutGuide 的行为有所不同，但显然确实如此。还证明我不需要设置约束； scrollView.layoutIfNeeded() 成功了！我的 scrollView 现在是一个恒定的 375x667，消除了调整大小的问题并给出 self.topLayoutGuide.length = 64。这允许我通过在 centerScrollViewContents() 中减去 self.topLayoutGuide.length 来使视图垂直居中。我也在viewWillLayoutSubviews()中调用了centerScrollViewContents()。这是我的新代码：

@IBOutlet var scrollView: UIScrollView!

var imageView: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()

    //Redo constraints at runtime
    scrollView.layoutIfNeeded()

    //Original Ray Wenderlich code
    let image1 = UIImage(named: "photo1")!
    imageView = UIImageView(image: image1)
    imageView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size: image1.size)
    scrollView.addSubview(imageView)
    scrollView.contentSize = image1.size

    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.height / scrollView.contentSize.height
    let minScale = min(scaleWidth, scaleHeight)
    scrollView.minimumZoomScale = minScale
    scrollView.maximumZoomScale = 1.0
    scrollView.zoomScale = minScale
}
func centerScrollViewContents() {
    let boundsSize = scrollView.bounds.size
    var contentsFrame =  imageView.frame

    if contentsFrame.size.width < boundsSize.width {
        contentsFrame.origin.x = (boundsSize.width - contentsFrame.width) / 2.0
    } else {
        contentsFrame.origin.x = 0.0
    }

    if contentsFrame.size.height < boundsSize.height {
        contentsFrame.origin.y = (boundsSize.height - contentsFrame.height - self.topLayoutGuide.length) / 2.0
    } else {
        contentsFrame.origin.y = 0.0
    }

    imageView.frame = contentsFrame
}

override func viewWillLayoutSubviews() {
    println(self.topLayoutGuide.length)
    centerScrollViewContents()
}

所有其他功能均未更改。