@IBDesignable class ExUILabel: UILabel {

    @IBInspectable var fontName: String = "myFontName" {
        didSet {
            self.font = UIFont(name: fontName, size: self.font.pointSize)
        }
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        self.font = UIFont(name: fontName, size: (self.font?.pointSize)!)
        self.adjustsFontSizeToFitWidth = true
    }
}

self.font = UIFont(name: fontName, size: (self.font?.pointSize)!)