swift - NSLayoutConstraint 和 safeAreaLayoutGuide - 编码兼容 pre-iOS 11

Question

如果我想要一个与 iOS 11 之前的设备兼容的应用程序，我是否需要此代码用于将视图的某些属性链接到 self.view 的每个约束以遵守 safeAreaLayoutGuide？

if #available(iOS 11.0, *) {
     NSLayoutConstraint.activate([
          theImage.heightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.heightAnchor, multiplier: 0.5)
          theImage.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -20),
          theImage.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -view.frame.width/8)
     ])
} else {
     NSLayoutConstraint.activate([
          theImage.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.5)
          theImage.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20),
          theImage.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -view.frame.width/8),
     ])
}

Answer 1

该代码看起来正确。如果您担心到处都有重复，可以通过一些方法来整合它。你可以这样做：

extension UIViewController {

    var correctLayoutGuide: UILayoutGuide {
        if #available(iOS 11.0, *) {
            return view.safeAreaLayoutGuide
        }
        else {
            return view.layoutMarginsGuide
        }
    }

}

那么您的代码片段可能只是：

NSLayoutConstraint.activate([
      theImage.heightAnchor.constraint(equalTo: correctLayoutGuide.heightAnchor, multiplier: 0.5)
      theImage.bottomAnchor.constraint(equalTo: correctLayoutGuide.bottomAnchor, constant: -20),
      theImage.trailingAnchor.constraint(equalTo: correctLayoutGuide.trailingAnchor, constant: 20)
 ])