UIImage在尝试添加层掩码时消失

我创建了这个函数来在 UIImageView

func roundCorners(corners: [UIRectCorner], imageView: UIImageView) -> CAShapeLayer {
    let maskPath = UIBezierPath.init(roundedRect: imageView.bounds, byRoundingCorners:[.topLeft], cornerRadii: CGSize.init(width: 7.0, height: 7.0))
    let maskLayer = CAShapeLayer()
    maskLayer.frame = imageView.frame
    maskLayer.path = maskPath.cgPath
    return maskLayer
}

topLeftImage 这样地: topLeftImage.layer.mask = roundCorners(corners: [.topLeft], imageView: topLeftImage)

let topLeftImage: UIImageView = {
    let iv = UIImageView()
    iv.image = #imageLiteral(resourceName: "myImage")
    iv.layoutIfNeeded()
    iv.translatesAutoresizingMaskIntoConstraints = false
    iv.contentMode = UIViewContentMode.scaleAspectFill
    iv.layer.masksToBounds = true
    iv.clipsToBounds = true
    return iv
}()