Convert HTML to NSAttributedString in iOS

Question

I am using a instance of UIWebView to process some text and color it correctly, it gives the result as HTML but rather than displaying it in the UIWebView I want to display it using Core Text with a NSAttributedString.

I am able to create and draw the NSAttributedString but I am unsure how I can convert and map the HTML into the attributed string.

I understand that under Mac OS X NSAttributedString has a initWithHTML: method but this was a Mac only addition and is not available for iOS.

I also know that there is a similar question to this but it had no answers, I though I would try again and see whether anyone has created a way to do this and if so, if they could share it.

Answer 1

Using of NSHTMLTextDocumentType is slow and it is hard to control styles. I suggest you to try my library which is called Atributika. It has its own very fast HTML parser. Also you can have any tag names and define any style for them.

Example:

let str = "<strong>Hello</strong> World!".style(tags:
    Style("strong").font(.boldSystemFont(ofSize: 15))).attributedString

label.attributedText = str

You can find it here https://github.com/psharanda/Atributika

Answer 2

Swift 3:
Try this:

extension String {
    func htmlAttributedString() -> NSAttributedString? {
        guard let data = self.data(using: String.Encoding.utf16, allowLossyConversion: false) else { return nil }
        guard let html = try? NSMutableAttributedString(
            data: data,
            options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType],
            documentAttributes: nil) else { return nil }
        return html
    }
}  

And for using:

let str = "<h1>Hello bro</h1><h2>Come On</h2><h3>Go sis</h3><ul><li>ME 1</li><li>ME 2</li></ul> <p>It is me bro , remember please</p>"

self.contentLabel.attributedText = str.htmlAttributedString()

Answer 3

The only solution you have right now is to parse the HTML, build up some nodes with given point/font/etc attributes, then combine them together into an NSAttributedString. It's a lot of work, but if done correctly, can be reusable in the future.

Answer 4

This is a String extension written in Swift to return a HTML string as NSAttributedString.

extension String {
    func htmlAttributedString() -> NSAttributedString? {
        guard let data = self.dataUsingEncoding(NSUTF16StringEncoding, allowLossyConversion: false) else { return nil }
        guard let html = try? NSMutableAttributedString(data: data, options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType], documentAttributes: nil) else { return nil }
        return html
    }
}

To use,

label.attributedText = "<b>Hello</b> \u{2022} babe".htmlAttributedString()

In the above, I have purposely added a unicode \u2022 to show that it renders unicode correctly.

A trivial: The default encoding that NSAttributedString uses is NSUTF16StringEncoding (not UTF8!).

Answer 5

The above solution is correct.

[[NSAttributedString alloc] initWithData:[htmlString dataUsingEncoding:NSUTF8StringEncoding] 
                                 options:@{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,
                                           NSCharacterEncodingDocumentAttribute: @(NSUTF8StringEncoding)} 
                      documentAttributes:nil error:nil];

But the app wioll crash if you are running it on ios 8.1,2 or 3.

To avoid the crash what you can do is : run this in a queue. So that it always be on main thread.

Answer 6

Helpful Extensions

Inspired by this thread, a pod, and Erica Sadun's ObjC example in iOS Gourmet Cookbook p.80, I wrote an extension on String and on NSAttributedString to go back and forth between HTML plain-strings and NSAttributedStrings and vice versa -- on GitHub here, which I have found helpful.

The signatures are (again, full code in a Gist, link above):

extension NSAttributedString {
    func encodedString(ext: DocEXT) -> String?
    static func fromEncodedString(_ eString: String, ext: DocEXT) -> NSAttributedString? 
    static func fromHTML(_ html: String) -> NSAttributedString? // same as above, where ext = .html
}

extension String {
    func attributedString(ext: DocEXT) -> NSAttributedString?
}

enum DocEXT: String { case rtfd, rtf, htm, html, txt }