如何仅为图层的左下角、右下角和左上角设置圆角？

extension UIView {

func roundCorners(_ corners: CACornerMask, radius: CGFloat) {
    if #available(iOS 11, *) {
        self.layer.cornerRadius = radius
        self.layer.maskedCorners = corners
    } else {
        var cornerMask = UIRectCorner()
        if(corners.contains(.layerMinXMinYCorner)){
            cornerMask.insert(.topLeft)
        }
        if(corners.contains(.layerMaxXMinYCorner)){
            cornerMask.insert(.topRight)
        }
        if(corners.contains(.layerMinXMaxYCorner)){
            cornerMask.insert(.bottomLeft)
        }
        if(corners.contains(.layerMaxXMaxYCorner)){
            cornerMask.insert(.bottomRight)
        }
        let path = UIBezierPath(roundedRect: self.bounds, byRoundingCorners: cornerMask, cornerRadii: CGSize(width: radius, height: radius))
        let mask = CAShapeLayer()
        mask.path = path.cgPath
        self.layer.mask = mask
    }
}

}

问题已解决，现在右上角和右下角可以正常工作。

代码已在iOS 9、10、11版本中进行了测试。

 extension UIView {
        func roundCorners(_ corners:UIRectCorner,_ cormerMask:CACornerMask, radius: CGFloat) {
            if #available(iOS 11.0, *){
                self.clipsToBounds = false
                self.layer.cornerRadius = radius
                self.layer.maskedCorners = cormerMask
            }else{
                let rectShape = CAShapeLayer()
                rectShape.bounds = self.frame
                rectShape.position = self.center
                rectShape.path = UIBezierPath(roundedRect: self.bounds,    byRoundingCorners: corners, cornerRadii: CGSize(width: radius, height: radius)).cgPath
                self.layer.mask = rectShape
            }
        }
        
    }

正如@kazi.munshimun提出的只读设置建议一样，这是很棒的，但我不想为此创建一个完整的视图，我正在寻找一个仅有的cornerRadius字段。

因此，我想到了标志组合的想法，例如BottomLeft(4) + BottomRight(8) = 12

因此，在您的视图上设置数字组合从0（无）到15（所有角落）+启用clipsToBounds即可。就是这样！通过文件完全可定制。

此解决方案示例适用于iOS 11.0+（Swift 4+），可以适应较低版本：

extension UIView {
    enum CornerEnum: Int  {
        case None = 0
        case TopLeft = 1
        case TopRight = 2
        case BottomLeft = 4
        case BottomRight = 8
    }
    
    @IBInspectable
    var radiusCorners: Int {
        set {
            var corners = CACornerMask()
            if(newValue & CornerEnum.TopLeft.rawValue != 0){
                corners.insert(.layerMinXMinYCorner)
            }
            if(newValue & CornerEnum.TopRight.rawValue != 0){
                corners.insert(.layerMaxXMinYCorner)
            }
            if(newValue & CornerEnum.BottomLeft.rawValue != 0){
                corners.insert(.layerMinXMaxYCorner)
            }
            if(newValue & CornerEnum.BottomRight.rawValue != 0){
                corners.insert(.layerMaxXMaxYCorner)
            }
            layer.maskedCorners = corners
        }
        get { return self.radiusCorners }
    }
}