safeAreaLayoutGuide

Question

我已经这样设置了 safeAreaLayoutGuide：

let guide = view.safeAreaLayoutGuide

NSLayoutConstraint.activate([
  topControls.topAnchor.constraint(equalTo: guide.topAnchor, constant: 0)
])

效果很好。但是，当我将设备旋转到横向模式时，没有状态栏（电池、信号等）并且屏幕顶部的偏移量为零。这是正确的，基于锚点。然而，它看起来并不好。如何在创建锚点期间为景观添加偏移量 20？我不想手动更改基于方向的常量。

Answer 1

假设您运行在 iPhone 上，那么这是预期的行为，可以通过覆盖以下内容来更改：

override var prefersStatusBarHidden: Bool {
    return false
}

根据该 UIViewController 方法的描述：

By default, this method returns false with one exception. For apps linked against iOS 8 or later, this method returns true if the view controller is in a vertically compact environment.

如果您覆盖它，那么您将获得一个横向状态栏，并且安全区域指南将相应地进行调整。

编辑

所以对原来的要求有点误解。不是显示状态栏而是像有状态栏一样有个空隙

这需要手动完成，因为您无法手动设置仅适用于某些 orientations/size class 的约束。

这是一个基本的 UIViewController，可以满足您的需求：

class ViewController: UIViewController {
    var testView: UIView!
    var landscapeConstraint: NSLayoutConstraint!
    var portraitConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        self.testView = UIView()
        self.testView.backgroundColor = .green
        self.view.addSubview(self.testView)
        self.testView.translatesAutoresizingMaskIntoConstraints = false

        let guide = view.safeAreaLayoutGuide

        self.testView.leftAnchor.constraint(equalTo: guide.leftAnchor, constant: 0).isActive = true
        self.testView.rightAnchor.constraint(equalTo: guide.rightAnchor, constant: 0).isActive = true
        self.testView.bottomAnchor.constraint(equalTo: guide.bottomAnchor, constant: 0).isActive = true

        self.portraitConstraint = self.testView.topAnchor.constraint(equalTo: guide.topAnchor, constant: 0)
        self.landscapeConstraint = self.testView.topAnchor.constraint(equalTo: guide.topAnchor, constant: 20) // Hardcoded the size but this can be anything you want.

        switch self.traitCollection.verticalSizeClass {
        case .compact:
            self.landscapeConstraint.isActive = true
        case.regular:
            self.portraitConstraint.isActive = true
        default: // This shouldn't happen but let's assume regular (i.e. portrait)
            self.portraitConstraint.isActive = true
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {
        super.willTransition(to: newCollection, with: coordinator)

        switch newCollection.verticalSizeClass {
        case .compact:
            self.portraitConstraint.isActive = false
            self.landscapeConstraint.isActive = true
        case.regular:
            self.landscapeConstraint.isActive = false
            self.portraitConstraint.isActive = true
        default: // This shouldn't happen but let's assume regular (i.e. portrait)
            self.landscapeConstraint.isActive = false
            self.portraitConstraint.isActive = true
        }
    }
}

基本上你设置了固定的约束，即左、右和底部，然后设置纵向和横向的约束（常规和紧凑的垂直尺寸 class），这两个约束在默认情况下都是禁用的。然后你根据当前orientation/sizeclass决定激活哪一个。然后你覆盖：

willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator)

基于新orientation/sizeclass.

的两个约束的方法和swap active state

需要注意的一件事是始终先停用约束，然后再激活约束以避免任何抱怨无法满足的约束。

safeAreaLayoutGuide - 横向模式

safeAreaLayoutGuide - landscape mode

ios

swift

autolayout