iOS 实现部分圆角

方法一：maskedCorners

self.layerView.layer.cornerRadius = 16
self.layerView.layer.maskedCorners = [.layerMinXMaxYCorner, .layerMaxXMaxYCorner]

CACornerMask 可以分别指定四个角：

public struct CACornerMask : OptionSet {

    public init(rawValue: UInt)

    
    public static var layerMinXMinYCorner: CACornerMask { get }

    public static var layerMaxXMinYCorner: CACornerMask { get }

    public static var layerMinXMaxYCorner: CACornerMask { get }

    public static var layerMaxXMaxYCorner: CACornerMask { get }
}

方法二：UIBezierPath

let path = UIBezierPath(roundedRect: self.layerView.bounds, byRoundingCorners: [UIRectCorner.topLeft, UIRectCorner.topRight], cornerRadii: CGSize(width: 16, height: 16))
let maskLayer = CAShapeLayer()
maskLayer.frame = self.layerView.bounds
maskLayer.path = path.cgPath
self.layerView.layer.mask = maskLayer

UIRectCorner 也可以分别指定四个角

public struct UIRectCorner : OptionSet {

    public init(rawValue: UInt)

    
    public static var topLeft: UIRectCorner { get }

    public static var topRight: UIRectCorner { get }

    public static var bottomLeft: UIRectCorner { get }

    public static var bottomRight: UIRectCorner { get }

    public static var allCorners: UIRectCorner { get }
}