DocumentReadingOptionKey键在swift4迁移后损坏

let options: [NSAttributedString.DocumentReadingOptionKey: AnyHashable] =
                          [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue]

            let str = try NSAttributedString( data:string!.data(using: String.Encoding.utf8, allowLossyConversion: true
                )!, options:options, documentAttributes: nil)

iOS 9没有问题,运行iOS 8.3时,控制台输出：“dyld：找不到符号：_NSCharacterEncodingDocumentOption”;它将在评论“.characterEncoding：String.Encoding.utf8.rawValue”之后传递.

例：

public func htmlToString() -> String? {
        guard let data = data(using: .utf8) else { return nil }
        do {
            return try NSAttributedString(
                data: data,
                options: [
                    .documentType: NSAttributedString.DocumentType.html
                ],
                documentAttributes: nil
            ).string
        } catch let error as NSError {
            print(error.localizedDescription)
            return  nil
        }
    }

祝你有美好的一天！