ios - UIScrollView 与 UILabel 布局不明确

Question

我正在尝试用代码设置所有内容。在我的 viewController 中，我声明了以下属性:

var scrollView: UIScrollView!
var font: UIFont?
var label: UILabel!
var fontSize: CGFloat = 50

我的 viewDidLoad 看起来像:

override func viewDidLoad() {
    super.viewDidLoad()

    font = UIFont(name: "HelveticaNeue-UltraLight", size: fontSize)!

    scrollView = UIScrollView()
    scrollView.translatesAutoresizingMaskIntoConstraints = false
    scrollView.backgroundColor = UIColor.lightGray
    view.addSubview(scrollView)

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

    label = UILabel(frame: CGRect.zero)
    label.font = font
    label.lineBreakMode = .byWordWrapping
    label.translatesAutoresizingMaskIntoConstraints = false
    label.numberOfLines = 0
    label.text = """
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam rutrum urna nec risus dapibus, nec sagittis risus vulputate. Nullam volutpat eros nec sagittis eleifend. Nam sit amet convallis sem, quis tempus quam. Cras egestas est at ipsum tincidunt maximus. Vivamus suscipit justo vel sapien blandit, sed vehicula ipsum euismod. Etiam faucibus tortor at augue ullamcorper, at feugiat lorem varius. Quisque at purus vestibulum, varius ex quis, viverra nibh. Nulla ac porta enim. Nulla egestas mauris a pretium rutrum. Interdum et malesuada fames ac ante ipsum primis in faucibus. Etiam lacinia augue nec augue dictum condimentum. Ut aliquam ac lacus a venenatis. Pellentesque egestas libero sed sem rutrum tempus. Duis posuere turpis at lacinia varius.
"""
    scrollView.addSubview(label)
    label.setContentHuggingPriority(UILayoutPriority(rawValue: 249.0), for: .vertical)
    label.setContentCompressionResistancePriority(UILayoutPriority(rawValue: 751.0), for: .horizontal)
    label.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 48.0).isActive = true
    label.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16.0).isActive = true
    label.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16.0).isActive = true
    label.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor)
    label.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor, constant: -48.0).isActive = true
}

因此，如果我在模拟器中运行它，它会按我的预期工作，控制台中没有模糊的布局。但有几件事不起作用。

如果我将 label.text 添加到更多段落，如下所示:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam rutrum urna nec risus dapibus, nec sagittis risus vulputate. Nullam volutpat eros nec sagittis eleifend. Nam sit amet convallis sem, quis tempus quam. Cras egestas est at ipsum tincidunt maximus. Vivamus suscipit justo vel sapien blandit, sed vehicula ipsum euismod. Etiam faucibus tortor at augue ullamcorper, at feugiat lorem varius. Quisque at purus vestibulum, varius ex quis, viverra nibh. Nulla ac porta enim. Nulla egestas mauris a pretium rutrum. Interdum et malesuada fames ac ante ipsum primis in faucibus. Etiam lacinia augue nec augue dictum condimentum. Ut aliquam ac lacus a venenatis. Pellentesque egestas libero sed sem rutrum tempus. Duis posuere turpis at lacinia varius.

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Pellentesque vitae ligula mollis, vehicula mi at, venenatis justo. Nullam id imperdiet odio. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Aenean arcu est, venenatis at sem commodo, condimentum feugiat arcu.

Suspendisse quis malesuada ipsum. Quisque lobortis est in dapibus fermentum. Sed lacinia lacus leo, ac euismod metus faucibus vitae. Curabitur fermentum vulputate vestibulum. Nullam quis turpis ac tortor pharetra accumsan. Aenean finibus lacus quis orci accumsan, iaculis dignissim purus lacinia. Maecenas convallis risus in pulvinar pharetra. Curabitur eu maximus risus. Nunc convallis finibus venenatis. Phasellus nec posuere est, at blandit magna. Nulla rutrum mi id sapien vestibulum eleifend. Nullam sapien nunc, feugiat ut elementum vitae, ultrices in tortor. Integer massa leo, mollis vitae mattis vel, sagittis eu libero. Cras tellus lacus, sodales at nisi ut, dictum mattis risus.

Curabitur at euismod purus, quis posuere nulla. Donec quam mauris, faucibus sed tellus sed, finibus convallis nulla. Ut vehicula consectetur ultricies. Morbi malesuada lorem eget cursus pharetra. Curabitur vitae convallis lacus, in aliquet arcu. Sed interdum ut mauris bibendum tincidunt. Proin consectetur elit diam, eget mattis augue euismod et. Nullam et iaculis dolor, ac scelerisque erat. In non volutpat velit, vitae vulputate augue. Quisque sollicitudin nunc erat, a cursus lorem faucibus sit amet. Suspendisse id augue non nisl congue tincidunt. Duis vulputate massa eu finibus semper. Integer tristique, massa a efficitur accumsan, ligula libero imperdiet enim, quis semper quam risus in sapien. Suspendisse potenti.

Aliquam magna elit, euismod non egestas id, sollicitudin vitae metus. Cras enim magna, placerat sit amet vestibulum non, pellentesque ac lacus. Aenean ut eros auctor diam tincidunt egestas et ac enim. Nunc tempor lorem eget purus eleifend, facilisis efficitur dui feugiat. Sed viverra suscipit luctus. Donec dignissim lorem a urna elementum, id efficitur turpis vestibulum. Praesent laoreet faucibus orci, vel dictum neque ullamcorper in.

标签不再呈现。

或者，如果我只使用一个段落，但将字体大小增加到 100，则标签也不会呈现。

最后，即使标签只有一个段落，字体大小为 50，即使它看起来运行良好，如果我单击“ View 调试器”，我会得到“可滚动内容大小对于 UIScrollView 来说不明确”。

我是否缺少 UILabels 和 UIScrollViews 的某些内容？我还缺少其他事件、属性或约束吗？

Answer 1

稍微修改一下您的代码后，我发现您遇到了一些问题。

字体未在模拟器中呈现:

这显然是模拟器错误。我在 Xcode 10.2.1/Mojave 10.14.4 上看到它。文本未呈现，但标签大小正确，因此您可以 ScrollView 并看到垂直指示器向下/向上移动。即使您指定大于 32 的系统字体，也会出现此问题。在真实设备上(在运行 iOS 12.2 的 iPhone XS 上测试)，文本可以正确呈现。

请在 https://bugreport.apple.com 提交有关该问题的错误报告，提供该问题的示例代码。

UIScrollView 的可滚动内容大小不明确:

ScrollView 的内容需要固定到 ScrollView 的每个边缘。您嵌入的标签的前导和尾随约束仅限于 Root View ，而不是 ScrollView 。它们应该被限制在 ScrollView 上，如下所示:

label.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 48.0).isActive = true
label.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 16.0).isActive = true
label.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: -16.0).isActive = true
label.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: -48.0).isActive = true

虽然上述更改将解决不明确的内容大小问题，但我建议您立即激活所有约束，因为这样更有效:

NSLayoutConstraint.activate([
  scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
  scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
  scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
  scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
  label.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 48.0),
  label.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 16.0),
  label.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: -16.0),
  label.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor),
  label.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: -48.0)
])

我没有发现 contentHuggingPriority 或 contentCompressionResistancePriority 行是必要的，但也许您有理由包含这些内容。

通过这些更改，不明确的内容警告就会消失。在我的 iPhone XS 上，纵向和横向的布局看起来都是正确的。