试试这段代码，

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:view.bounds byRoundingCorners:( UIRectCornerTopLeft | UIRectCornerTopRight) cornerRadii:CGSizeMake(5.0, 5.0)];

CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = self.view.bounds;
maskLayer.path  = maskPath.CGPath;

view.layer.mask = maskLayer;

所有已经给出的答案都是非常好的和有效的(特别是尤努斯使用蒙版属性的想法)。

然而，我需要一些更复杂的东西，因为我的层可以经常改变大小，这意味着我需要每次都调用掩蔽逻辑，这有点烦人。

我使用了swift扩展和计算属性来构建一个真正的cornerRadii属性，它负责在图层布局时自动更新蒙版。

这是使用Peter Steinberg伟大的Aspects库实现的。

完整代码在这里:

extension CALayer {
  // This will hold the keys for the runtime property associations
  private struct AssociationKey {
    static var CornerRect:Int8 = 1    // for the UIRectCorner argument
    static var CornerRadius:Int8 = 2  // for the radius argument
  }

  // new computed property on CALayer
  // You send the corners you want to round (ex. [.TopLeft, .BottomLeft])
  // and the radius at which you want the corners to be round
  var cornerRadii:(corners: UIRectCorner, radius:CGFloat) {
    get {
      let number = objc_getAssociatedObject(self, &AssociationKey.CornerRect)  as? NSNumber ?? 0
      let radius = objc_getAssociatedObject(self, &AssociationKey.CornerRadius)  as? NSNumber ?? 0
      return (corners: UIRectCorner(rawValue: number.unsignedLongValue), radius: CGFloat(radius.floatValue))
    }
    set (v) {
      let radius = v.radius
      let closure:((Void)->Void) = {
        let path = UIBezierPath(roundedRect: self.bounds, byRoundingCorners: v.corners, cornerRadii: CGSize(width: radius, height: radius))
        let mask = CAShapeLayer()
        mask.path = path.CGPath
        self.mask = mask
      }
      let block: @convention(block) Void -> Void = closure
      let objectBlock = unsafeBitCast(block, AnyObject.self)
      objc_setAssociatedObject(self, &AssociationKey.CornerRect, NSNumber(unsignedLong: v.corners.rawValue), .OBJC_ASSOCIATION_RETAIN)
      objc_setAssociatedObject(self, &AssociationKey.CornerRadius, NSNumber(float: Float(v.radius)), .OBJC_ASSOCIATION_RETAIN)
      do { try aspect_hookSelector("layoutSublayers", withOptions: .PositionAfter, usingBlock: objectBlock) }
      catch _ { }
    }
  }
}

我写了一篇简单的博客来解释这一点。

Emma: . topright和。bottom right对你不起作用，可能是因为视图调用。roundCorners是在最终视图边界计算之前完成的。注意，贝塞尔路径在被调用时起源于视图边界。例如，如果自动布局将缩小视图，右侧的圆角可能在视图之外。 尝试在viewDidLayoutSubviews中调用它，其中视图的边界是final。

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)
    }
    
}

在swift 4.3中，修改代码后@apinho工作正常

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

为您的视图使用此函数

YourViewName. roundCornersWithLayerMask(cornerRadii: 20,corners: [.topLeft,.topRight])

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