如何使用UIButton.Configuration给标题加下划线？

Question

这是我对 UIButton 的方便初始化：

convenience init(underlinedTitle: String, font: UIFont, color: UIColor) {
    var configuration = UIButton.Configuration.plain()
    configuration.title = underlinedTitle
    configuration.titleTextAttributesTransformer = UIConfigurationTextAttributesTransformer { incoming in
        var outgoing = incoming
        outgoing.font = font
        outgoing.foregroundColor = color
        outgoing.underlineStyle = .single
        outgoing.underlineColor = color
        return outgoing
    }
    self.init(configuration: configuration)
}

效果如下：

为什么没有下划线？

Answer 1

尝试使用此答案中的方法 https://stackoverflow.com/a/41166179/11335258

@IBOutlet weak var yourButton: UIButton!

var attrs = [
NSFontAttributeName : UIFont.systemFontOfSize(19.0),
NSForegroundColorAttributeName : UIColor.redColor(),
NSUnderlineStyleAttributeName : 1]

var attributedString = NSMutableAttributedString(string:"")

override func viewDidLoad() {
  super.viewDidLoad()

  let buttonTitleStr = NSMutableAttributedString(string:"My Button", attributes:attrs)
  attributedString.appendAttributedString(buttonTitleStr)
  yourButton.setAttributedTitle(attributedString, forState: .Normal)
}