HTML string to NSAttributedString

Swift+HTML.swift

// Swift 4
extension String {

    func toAttributedString(color: UIColor?, font: UIFont?) -> NSAttributedString {
        
        do {
            
            var string = self
            if color != nil, font != nil {
                string = """
                    <style>
                        body {
                            color:\(color!.hex);
                            font-size:\(font!.pointSize)px;
                            font-family:'\(font!.fontName)';
                        }
                    </style>\(self)
                """
            }
            
            guard let data = string.data(using: .utf8) else {
                return NSAttributedString(string: self)
            }
            
            let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue]
            
            let attrString = try NSMutableAttributedString(data: data, options: options, documentAttributes: nil)

            return attrString
        } catch {
            print("error:", error)
            return  NSAttributedString(string: self)
        }
    }
}

You don't have to go to HTML first to set a font on an attributed string. You can just use something like:

func toAttributedString(color: UIColor?, font: UIFont?) -> NSAttributedString {
   var attributedText = NSMutableAttributedString(string: self)
   attributedText.addAttribute(NSAttributedStringKey.font, value: font, range: NSRange(location: 0, length: attributedText.length))
   attributedText.addAttribute(NSAttributedStringKey.foregroundColor.rawValue, value: color, range: NSRange(location: 0, length: attributedText.length))
   return attributedText
}

For an easy to use attributed text helper see:
https://github.com/evermeer/AttributedTextView