原地址：http://www.lxweimin.com/p/2b939f53debf

extension UIView{
    public  func extSetPartCornerRadiusHan(byRoundingCorners corners: UIRectCorner, radii: CGFloat) {
        let maskPath = UIBezierPath(roundedRect: self.bounds, byRoundingCorners: corners, cornerRadii: CGSize.init(width: radii, height: radii))
        let maskLayer = CAShapeLayer()
        maskLayer.frame = self.bounds
        maskLayer.path = maskPath.cgPath
        self.layer.mask = maskLayer
    }
}

注意： 添加圓角的View如果是用約束做的布局，那么在VC里面在viewDidLayoutSubviews函數下調用

 override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        self.firstView.extSetPartCornerRadiusHan(byRoundingCorners: [UIRectCorner.bottomLeft,UIRectCorner.bottomRight], radii: 10)
    }

在View里面添加在這個函數下面

override func layoutSubviews() {
        super.layoutSubviews()
    }

原因： 用約束去做布局，視圖的frame 和 bounds 不會立刻繪制，所以 width height 是0 看不到效果