将可视格式的约束转换为 NSLayoutAnchor API

Question

我有以下从 this SO question a few months ago 获得的扩展，我想将其转换为 NSLayoutAnchor（或更详细的布局 APIs），原因很简单视觉格式不支持指定安全区域布局指南。

link中的分机是这个：

extension UIView {

    /// Adds constraints to this `UIView` instances `superview` object to make sure this always has the same size as the superview.
    /// Please note that this has no effect if its `superview` is `nil` – add this `UIView` instance as a subview before calling this.
    func bindFrameToSuperviewBounds() {
        guard let superview = self.superview else {
            print("Error! `superview` was nil – call `addSubview(view: UIView)` before calling `bindFrameToSuperviewBounds()` to fix this.")
            return
        }

        self.translatesAutoresizingMaskIntoConstraints = false
        superview.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-0-[subview]-0-|", options: .directionLeadingToTrailing, metrics: nil, views: ["subview": self]))
        superview.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-0-[subview]-0-|", options: .directionLeadingToTrailing, metrics: nil, views: ["subview": self]))
    }
}

我的视图层次结构是：

UINavigationController -> 根视图控制器：UIPageViewController -> 第一页：UIViewController -> UIScrollView -> UIImageView

当我调用bindFrameToSuperviewBounds()时，结果如下：

大部分看起来还不错。问题是图像视图位于导航栏下方，这是我不想要的。所以为了解决这个问题，我尝试将 bindFrameToSuperviewBounds() 重写为：

guard let superview = self.superview else {
            fatalError("Attempting to bound to a non-existing superview.")
        }

translatesAutoresizingMaskIntoConstraints = false
self.topAnchor.constraint(equalTo: superview.safeAreaLayoutGuide.topAnchor).isActive = true
self.leadingAnchor.constraint(equalTo: superview.safeAreaLayoutGuide.leadingAnchor).isActive = true
self.bottomAnchor.constraint(equalTo: superview.safeAreaLayoutGuide.bottomAnchor).isActive = true
self.trailingAnchor.constraint(equalTo: superview.safeAreaLayoutGuide.trailingAnchor).isActive = true

结果是这样的：

这次它正确地没有进入导航栏下方，但是......你可以看到它被拉长了，这是我不想要的。

将视觉布局 API 转换为可以考虑安全区域布局指南的正确方法是什么？

为了完成，设置滚动视图和图像视图的代码如下：

override func viewDidLoad() {
    super.viewDidLoad()
    imageScrollView.addSubview(imageView)
    imageScrollView.layoutIfNeeded()
    imageView.bindFrameToSuperviewBounds()
    view.addSubview(imageScrollView)
    imageView.layoutIfNeeded()
    imageScrollView.backgroundColor = .white
    imageScrollView.bindFrameToSuperviewBounds()
    imageScrollView.delegate = self
}

Answer 1

老实说，我不会为那些奇怪的 "visual" 布局而烦恼，它们很快就会消失。

这有帮助吗？

extension UIView {

    // put this view "inside" it's superview, simply stretched all four ways
    // amazingly useful

    func bindEdgesToSuperview() {

        guard let s = superview else {
            preconditionFailure("`superview` nil in bindEdgesToSuperview")
        }

        translatesAutoresizingMaskIntoConstraints = false
        leadingAnchor.constraint(equalTo: s.leadingAnchor).isActive = true
        trailingAnchor.constraint(equalTo: s.trailingAnchor).isActive = true
        topAnchor.constraint(equalTo: s.topAnchor).isActive = true
        bottomAnchor.constraint(equalTo: s.bottomAnchor).isActive = true
    }

}

就这样使用..

    textOnTop = ..  UILabel or whatever
    userPhoto.addSubview(textOnTop)
    textOnTop.bindEdgesToSuperview()

简单！

(PS - 不要忘记，如果它是图像：您几乎肯定想要在所有情况下始终将其设置为 AspectFit。）

安全布局指南的手柄就像...

.safeAreaLayoutGuide

Answer 2

通过 Fattie 提供的代码，我得到了这个解决方案：

guard let superview = self.superview else {
    fatalError("Attempting to bound to a non-existing superview.")
}

translatesAutoresizingMaskIntoConstraints = false
self.topAnchor.constraint(equalTo: superview.safeAreaLayoutGuide.topAnchor).isActive = true
self.leadingAnchor.constraint(equalTo: superview.leadingAnchor).isActive = true
self.bottomAnchor.constraint(equalTo: superview.bottomAnchor).isActive = true
self.trailingAnchor.constraint(equalTo: superview.trailingAnchor).isActive = true

（现在我只是将顶部锚定到安全布局是指南。这是否会给 iPhone X 带来问题还有待观察）。

这给出了我期望的结果：

将可视格式的约束转换为 NSLayoutAnchor API

Translating constraints in a visual format to NSLayoutAnchor APIs

ios

autolayout

visual-format-language

swift

nslayoutanchor