Convert NSAttributedString into Data for storage

I have a UITextView with attributed text and allowsEditingTextAttributes set to true.

I'm trying to convert the attributed string into a Data object, using the following code:

let text = self.textView.attributedText
let data = try text.data(from: NSMakeRange(0, text.length), documentAttributes: [:])

However, this is throwing the following error:

Error Domain=NSCocoaErrorDomain Code=66062 "(null)"

Any ideas what this error means or what could cause this? I'm on the latest Xcode and iOS. Thanks.

Solution

You need to specify what kind of document data you would like to convert your attributed string to:

.txt    // Plain Text Document Type (Simple Text)
.html   // HTML  Text Document Type (Hypertext Markup Language) 
.rtf    // RTF   Text Document Type (Rich text format document)
.rtfd   // RTFD  Text Document Type (Rich text format document with attachment)

update Xcode 10.2 • Swift 5 or later

let textView = UITextView()
textView.attributedText = .init(string: "abc",
                                attributes: [.font: UIFont(name: "Helvetica", size: 16)!])
if let attributedText = textView.attributedText {
    do {
        let htmlData = try attributedText.data(from: .init(location: 0, length: attributedText.length),
                                               documentAttributes: [.documentType: NSAttributedString.DocumentType.html])
        let htmlString = String(data: htmlData, encoding: .utf8) ?? ""
        print(htmlString)
    } catch {
        print(error)
    }
}

Expanding on that:

extension NSAttributedString {

    convenience init(data: Data, documentType: DocumentType, encoding: String.Encoding = .utf8) throws {
        try self.init(attributedString: .init(data: data, options: [.documentType: documentType, .characterEncoding: encoding.rawValue], documentAttributes: nil))
    }

    func data(_ documentType: DocumentType) -> Data {
        // Discussion
        // Raises an rangeException if any part of range lies beyond the end of the receiver’s characters.
        // Therefore passing a valid range allow us to force unwrap the result
        try! data(from: .init(location: 0, length: length),
                  documentAttributes: [.documentType: documentType])
    }

    var text: Data { data(.plain) }
    var html: Data { data(.html)  }
    var rtf:  Data { data(.rtf)   }
    var rtfd: Data { data(.rtfd)  }
}

Usage:

let textView = UITextView()
textView.attributedText = .init(string: "abc", attributes: [.font: UIFont(name: "Helvetica", size: 16)!])
if let textData = textView.attributedText?.text {
    let text = String(data: textData, encoding: .utf8) ?? ""
    print(text)  // abc
}
if let htmlData = textView.attributedText?.html {
    let html = String(data: htmlData, encoding: .utf8) ?? ""
    print(html)  // /* <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" ...
}

This will print

abc
/* <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="Content-Style-Type" content="text/css">
<title></title>
<meta name="Generator" content="Cocoa HTML Writer">
<style type="text/css">
p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 16.0px Helvetica}
span.s1 {font-family: 'Helvetica'; font-weight: normal; font-style: normal; font-size: 16.00pt}
</style>
</head>
<body>
<p class="p1"><span class="s1">abc</span></p>
</body>
</html>
*/