这是如何在c#中使用Xamarin为按钮的每个角落设置角半径:

var maskPath = UIBezierPath.FromRoundedRect(MyButton.Bounds, UIRectCorner.BottomLeft | UIRectCorner.BottomRight,
    new CGSize(10.0, 10.0));
var maskLayer = new CAShapeLayer
{
    Frame = MyButton.Bounds,
    Path = maskPath.CGPath
};
MyButton.Layer.Mask = maskLayer;

这是最简单的答案:

yourView.layer.cornerRadius = 8
yourView.layer.masksToBounds = true
yourView.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]

如果你正在寻找一个界面构建器的唯一解决方案，有一个适用于iOS 11或更高版本。在这里可以看到我的答案:https://stackoverflow.com/a/58626264

使用这个扩展设置角圆角和圆角边界

像这样使用:

override func viewWillLayoutSubviews() {
            super.viewWillLayoutSubviews()

         myView.roundCornersWithBorder(corners: [.topLeft, .topRight], radius: 8.0)
    
        myView.roundCorners(corners: [.topLeft, .topRight], radius: 8.0)

        }



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
    }
    
    func roundCornersWithBorder(corners: UIRectCorner, radius: CGFloat) {
        let maskLayer = CAShapeLayer()
        maskLayer.frame = bounds
        maskLayer.path = UIBezierPath(roundedRect: bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: radius, height: radius)).cgPath
        
        layer.mask = maskLayer
        
        // Add border
        let borderLayer = CAShapeLayer()
        borderLayer.path = maskLayer.path // Reuse the Bezier path
        borderLayer.fillColor = UIColor.clear.cgColor
        borderLayer.strokeColor = UIColor(red:3/255, green:33/255, blue:70/255, alpha: 0.15).cgColor
        borderLayer.lineWidth = 2
        borderLayer.frame = bounds
        layer.addSublayer(borderLayer)
    }
    
}

使用这个扩展，它将涵盖一切。

extension UIView {

   func roundTopCorners(radius: CGFloat = 10) {
    
       self.clipsToBounds = true
       self.layer.cornerRadius = radius
       if #available(iOS 11.0, *) {
           self.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
       } else {
           self.roundCorners(corners: [.topLeft, .topRight], radius: radius)
       }
   }

   func roundBottomCorners(radius: CGFloat = 10) {
    
       self.clipsToBounds = true
       self.layer.cornerRadius = radius
       if #available(iOS 11.0, *) {
           self.layer.maskedCorners = [.layerMinXMaxYCorner, .layerMaxXMaxYCorner]
       } else {
           self.roundCorners(corners: [.bottomLeft, .bottomRight], radius: radius)
       }
   }

   private 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
    }
}

然后像这样使用它:-

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
            
    self.yourView.roundTopCorners()
}

注意:-我建议你不要把这段代码放在viewDidLayoutSubviews()中，因为每当视图更新时，你都会在里面得到调用。所以使用viewDidAppear()，它会像一个咒语一样工作。

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)
    }
}