ios - Swift 如何检查 API 是否不可用

Question

我仅将圆角半径应用于 View 的左上角和右上角。在 viewDidLoad()我有:

if #available(iOS 11.0, *) {
    view.layer.cornerRadius = 20.0
    view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
} 

如果 iOS 11 不可用，最好的方法似乎是 draw(_ rect:) 。因为我必须在 viewDidLoad() 之外覆盖它，我想做以下事情

if NOT #available(iOS 11.0, *) {
    override func draw(_ rect: CGRect) {
        let maskPath = UIBezierPath(roundedRect: self.contentView.bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: 20.0, height: 20.0))
        let shapeLayer = CAShapeLayer()
        shapeLayer.frame = self.bounds
        shapeLayer.path = maskPath.cgPath
        view.layer.mask = shapeLayer
    }
}

这在语法上当然是不正确的。我该怎么办？

Answer 1

如果您需要支持 iOS 11 之前的版本，请在函数 draw(rect:) 中使用 #available 并使用 else 部分在早期版本上应用逻辑

override func draw(_ rect: CGRect) {
    if #available(iOS 11, *) {} else {
      let maskPath = UIBezierPath(roundedRect: self.contentView.bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: 20.0, height: 20.0))
      let shapeLayer = CAShapeLayer()
      shapeLayer.frame = self.bounds
      shapeLayer.path = maskPath.cgPath
      view.layer.mask = shapeLayer
    }
 }

更新 Swift 5.6:使用#unavailable

override func draw(_ rect: CGRect) {
   if #unavailable(iOS 11, *) {
      let maskPath = UIBezierPath(roundedRect: self.contentView.bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: 20.0, height: 20.0))
      let shapeLayer = CAShapeLayer()
      shapeLayer.frame = self.bounds
      shapeLayer.path = maskPath.cgPath
      view.layer.mask = shapeLayer
   }     
}