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 部分转换为具有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ViewController 类的UIViewController 与UIScrollView（没有自定义类）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

只有四个故事板约束（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() 和ViewController.swift 中。我现在总共有 8 个约束：

• 故事板上的4个约束：
  • 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

有了这些限制，在缩放之前，我的视图现在看起来像第三张专辑图片，scrollView 的帧大小仍然不正确375x667。放大后，我的视图是正确的，看起来像第四张专辑图像，scrollView 的帧大小在正确的375x603 上。其他一些注意事项：

• self.topLayoutGuide.length = 0。不应该是64吗？ 20 来自状态栏，44 来自导航栏？
• 删除情节提要约束会导致与没有程序约束相同的问题。为什么故事板约束仍然需要存在？
• 我尝试了纯方法和混合方法，但都没有解决这个问题。
• 除了在情节提要中禁用 Adjust Scroll View Insets、Extend Edges Under Top Bars 和 Extend Edges Under Opaque Bars（见第一张图片），我还在代码中禁用它们，但无济于事。
• 我不能使用插图，因为UIScrollView 的框架在缩放后会发生变化。

我怎样才能让UIScrollView 保持恒定、适当的大小？

谢谢。

类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

解决了！感谢Working with Top Layout Guide in UIScrollView through Auto Layout。我不认为 UIScrollView 会使topLayoutGuide 的行为有所不同，但显然确实如此。事实证明我不需要设置约束； scrollView.layoutIfNeeded() 成功了！我的 scrollView 现在是一个常数 375x667，消除了调整大小的问题并给出了 self.topLayoutGuide.length = 64。这允许我通过在 centerScrollViewContents() 中减去 self.topLayoutGuide.length 来垂直居中视图。我还在viewWillLayoutSubviews() 中打电话给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()
}

所有其他功能都没有改变。