iOS 11, Swift 4 你可以试试这段代码:

if #available(iOS 11.0, *) {
   element.clipsToBounds = true
   element.layer.cornerRadius = CORNER_RADIUS
   element.layer.maskedCorners = [.layerMaxXMaxYCorner]
} else {
   // Fallback on earlier versions
}

你可以在表格视图单元格中使用这个。

注意，如果你有布局约束附加到它，你必须在你的UIView子类中按如下方式刷新它:

override func layoutSubviews() {
    super.layoutSubviews()
    roundCorners(corners: [.topLeft, .topRight], radius: 3.0)
}

如果你不这样做，它就不会出现。

和圆角，使用扩展:

extension UIView {
   func roundCorners(corners: UIRectCorner, radius: CGFloat) {
        let path = UIBezierPath(roundedRect: bounds, byRoundingCorners: corners, cornerRadii: CGSize(width: radius, height: radius))
        let mask = CAShapeLayer()
        mask.path = path.cgPath
        layer.mask = mask
    }
}

附加的视图控制器情况:无论你不能或不想子类化一个视图，你仍然可以舍入一个视图。通过覆盖viewWillLayoutSubviews()函数，从它的视图控制器中完成，如下所示:

class MyVC: UIViewController {
    /// The view to round the top-left and top-right hand corners
    let theView: UIView = {
        let v = UIView(frame: CGRect(x: 10, y: 10, width: 200, height: 200))
        v.backgroundColor = .red
        return v
    }()
    
    override func loadView() {
        super.loadView()
        view.addSubview(theView)
    }
    
    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()

        // Call the roundCorners() func right there.
        theView.roundCorners(corners: [.topLeft, .topRight], radius: 30)
    }
}

对于 SwiftUI

我找到了这些解决方案，你可以在这里查看https://stackoverflow.com/a/56763282/3716103

我强烈推荐第一个

选项1:使用Path + GeometryReader

(更多关于GeometryReader的信息:https://swiftui-lab.com/geometryreader-to-the-rescue/)

struct ContentView : View {
    var body: some View {

        Text("Hello World!")
            .foregroundColor(.white)
            .font(.largeTitle)
            .padding(20)
            .background(RoundedCorners(color: .blue, tl: 0, tr: 30, bl: 30, br: 0))
    }
}

RoundedCorners

struct RoundedCorners: View {

    var color: Color = .white

    var tl: CGFloat = 0.0
    var tr: CGFloat = 0.0
    var bl: CGFloat = 0.0
    var br: CGFloat = 0.0

    var body: some View {
        GeometryReader { geometry in
            Path { path in

                let w = geometry.size.width
                let h = geometry.size.height

                // Make sure we do not exceed the size of the rectangle
                let tr = min(min(self.tr, h/2), w/2)
                let tl = min(min(self.tl, h/2), w/2)
                let bl = min(min(self.bl, h/2), w/2)
                let br = min(min(self.br, h/2), w/2)

                path.move(to: CGPoint(x: w / 2.0, y: 0))
                path.addLine(to: CGPoint(x: w - tr, y: 0))
                path.addArc(center: CGPoint(x: w - tr, y: tr), radius: tr, startAngle: Angle(degrees: -90), endAngle: Angle(degrees: 0), clockwise: false)
                path.addLine(to: CGPoint(x: w, y: h - be))
                path.addArc(center: CGPoint(x: w - br, y: h - br), radius: br, startAngle: Angle(degrees: 0), endAngle: Angle(degrees: 90), clockwise: false)
                path.addLine(to: CGPoint(x: bl, y: h))
                path.addArc(center: CGPoint(x: bl, y: h - bl), radius: bl, startAngle: Angle(degrees: 90), endAngle: Angle(degrees: 180), clockwise: false)
                path.addLine(to: CGPoint(x: 0, y: tl))
                path.addArc(center: CGPoint(x: tl, y: tl), radius: tl, startAngle: Angle(degrees: 180), endAngle: Angle(degrees: 270), clockwise: false)
            }
            .fill(self.color)
        }
    }
}

RoundedCorners_Previews

struct RoundedCorners_Previews: PreviewProvider {
    static var previews: some View {
        RoundedCorners(color: .pink, tl: 40, tr: 40, bl: 40, br: 40)
    }
}

下面是@JohnnyRockex的Swift版本的回答

extension UIView {

    func roundCorners(_ corners: UIRectCorner, radius: CGFloat) {
         let path = UIBezierPath(roundedRect: self.bounds, byRoundingCorners: corners, cornerRadii: CGSize(width: radius, height: radius))
         let mask = CAShapeLayer()
         mask.path = path.cgPath
         self.layer.mask = mask
    }

}

view.roundCorners([.topLeft, .bottomRight], radius: 10)

Note

如果你正在使用自动布局，你需要子类化你的UIView，并在视图的layoutSubviews中调用roundCorners以获得最佳效果。

class View: UIView {
    override func layoutSubviews() {
        super.layoutSubviews()

        self.roundCorners([.topLeft, .bottomLeft], radius: 10)
    }
}

有一个超级简单的方法。我在这里找到的。

view.clipsToBounds = true
view.layer.cornerRadius = 24
view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]

它在视图的CALayer上使用stock cornerRadius属性。你只需要定义这些角。layerMinXMinYCorner是左上layerMaxXMinYCorner是右上。

最后，在iOS11中有CACornerMask ! 使用CACornerMask可以很容易地完成:

let view = UIView()
view.clipsToBounds = true
view.layer.cornerRadius = 10
view.layer.maskedCorners = [.layerMaxXMinYCorner, .layerMinXMinYCorner] // Top right corner, Top left corner respectively