Convert HTML to NSAttributedString in iOS
IphoneObjective CCocoa TouchCore TextNsattributedstringIphone Problem Overview
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.
Iphone Solutions
Solution 1 - Iphone
In iOS 7, UIKit added an initWithData:options:documentAttributes:error:
method which can initialize an NSAttributedString
using HTML, eg:
[[NSAttributedString alloc] initWithData:[htmlString dataUsingEncoding:NSUTF8StringEncoding]
options:@{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,
NSCharacterEncodingDocumentAttribute: @(NSUTF8StringEncoding)}
documentAttributes:nil error:nil];
In Swift:
let htmlData = NSString(string: details).data(using: String.Encoding.unicode.rawValue)
let options = [NSAttributedString.DocumentReadingOptionKey.documentType:
NSAttributedString.DocumentType.html]
let attributedString = try? NSMutableAttributedString(data: htmlData ?? Data(),
options: options,
documentAttributes: nil)
Solution 2 - Iphone
There is a work-in-progress open source addition to NSAttributedString by Oliver Drobnik at Github. It uses NSScanner for HTML parsing.
Solution 3 - Iphone
Creating an NSAttributedString from HTML must be done on the main thread!
Update: It turns out that NSAttributedString HTML rendering depends on WebKit under the hood, and must be run on the main thread or it will occasionally crash the app with a SIGTRAP.
New Relic crash log:
Below is an updated thread-safe Swift 2 String extension:
extension String {
func attributedStringFromHTML(completionBlock:NSAttributedString? ->()) {
guard let data = dataUsingEncoding(NSUTF8StringEncoding) else {
print("Unable to decode data from html string: \(self)")
return completionBlock(nil)
}
let options = [NSDocumentTypeDocumentAttribute : NSHTMLTextDocumentType,
NSCharacterEncodingDocumentAttribute: NSNumber(unsignedInteger:NSUTF8StringEncoding)]
dispatch_async(dispatch_get_main_queue()) {
if let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) {
completionBlock(attributedString)
} else {
print("Unable to create attributed string from html string: \(self)")
completionBlock(nil)
}
}
}
}
Usage:
let html = "<center>Here is some <b>HTML</b></center>"
html.attributedStringFromHTML { attString in
self.bodyLabel.attributedText = attString
}
Output:
Solution 4 - Iphone
Swift initializer extension on NSAttributedString
My inclination was to add this as an extension to NSAttributedString
rather than String
. I tried it as a static extension and an initializer. I prefer the initializer which is what I've included below.
Swift 4
internal convenience init?(html: String) {
guard let data = html.data(using: String.Encoding.utf16, allowLossyConversion: false) else {
return nil
}
guard let attributedString = try? NSAttributedString(data: data, options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue], documentAttributes: nil) else {
return nil
}
self.init(attributedString: attributedString)
}
Swift 3
extension NSAttributedString {
internal convenience init?(html: String) {
guard let data = html.data(using: String.Encoding.utf16, allowLossyConversion: false) else {
return nil
}
guard let attributedString = try? NSMutableAttributedString(data: data, options: [NSAttributedString.DocumentReadingOptionKey.documentType: NSAttributedString.DocumentType.html], documentAttributes: nil) else {
return nil
}
self.init(attributedString: attributedString)
}
}
Example
let html = "<b>Hello World!</b>"
let attributedString = NSAttributedString(html: html)
Solution 5 - Iphone
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!).
Solution 6 - Iphone
Made some modification on Andrew's solution and update the code to Swift 3:
This code now use UITextView as self
and able to inherit its original font, font size and text color
Note: toHexString()
is extension from here
extension UITextView {
func setAttributedStringFromHTML(_ htmlCode: String, completionBlock: @escaping (NSAttributedString?) ->()) {
let inputText = "\(htmlCode)<style>body { font-family: '\((self.font?.fontName)!)'; font-size:\((self.font?.pointSize)!)px; color: \((self.textColor)!.toHexString()); }</style>"
guard let data = inputText.data(using: String.Encoding.utf16) else {
print("Unable to decode data from html string: \(self)")
return completionBlock(nil)
}
DispatchQueue.main.async {
if let attributedString = try? NSAttributedString(data: data, options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType], documentAttributes: nil) {
self.attributedText = attributedString
completionBlock(attributedString)
} else {
print("Unable to create attributed string from html string: \(self)")
completionBlock(nil)
}
}
}
}
Example usage:
mainTextView.setAttributedStringFromHTML("<i>Hello world!</i>") { _ in }
Solution 7 - Iphone
Swift 3.0 Xcode 8 Version
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
}
Solution 8 - Iphone
Swift 4
- NSAttributedString convenience initializer
- Without extra guards
- throws error
extension NSAttributedString {
convenience init(htmlString html: String) throws {
try self.init(data: Data(html.utf8), options: [
.documentType: NSAttributedString.DocumentType.html,
.characterEncoding: String.Encoding.utf8.rawValue
], documentAttributes: nil)
}
}
Usage
UILabel.attributedText = try? NSAttributedString(htmlString: "<strong>Hello</strong> World!")
Solution 9 - Iphone
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.
Solution 10 - Iphone
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
Solution 11 - Iphone
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.
Solution 12 - Iphone
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()
Solution 13 - Iphone
The built in conversion always sets the text color to UIColor.black, even if you pass an attributes dictionary with .forgroundColor set to something else. To support DARK mode on iOS 13, try this version of the extension on NSAttributedString.
extension NSAttributedString {
internal convenience init?(html: String) {
guard
let data = html.data(using: String.Encoding.utf16, allowLossyConversion: false) else { return nil }
let options : [DocumentReadingOptionKey : Any] = [
.documentType: NSAttributedString.DocumentType.html,
.characterEncoding: String.Encoding.utf8.rawValue
]
guard
let string = try? NSMutableAttributedString(data: data, options: options,
documentAttributes: nil) else { return nil }
if #available(iOS 13, *) {
let colour = [NSAttributedString.Key.foregroundColor: UIColor.label]
string.addAttributes(colour, range: NSRange(location: 0, length: string.length))
}
self.init(attributedString: string)
}
}
Solution 14 - Iphone
Here is the Swift 5
version of Mobile Dan's answer:
public extension NSAttributedString {
convenience init?(_ html: String) {
guard let data = html.data(using: .unicode) else {
return nil
}
try? self.init(data: data, options: [.documentType: NSAttributedString.DocumentType.html], documentAttributes: nil)
}
}
Solution 15 - Iphone
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 }
Solution 16 - Iphone
honoring font family, dynamic font I've concocted this abomination:
extension NSAttributedString
{
convenience fileprivate init?(html: String, font: UIFont? = Font.dynamic(style: .subheadline))
{
guard let data = html.data(using: String.Encoding.utf8, allowLossyConversion: true) else {
var totalString = html
/*
https://stackoverflow.com/questions/32660748/how-to-use-apples-new-san-francisco-font-on-a-webpage
.AppleSystemUIFont I get in font.familyName does not work
while -apple-system does:
*/
var ffamily = "-apple-system"
if let font = font {
let lLDBsucks = font.familyName
if !lLDBsucks.hasPrefix(".appleSystem") {
ffamily = font.familyName
}
totalString = "<style>\nhtml * {font-family: \(ffamily) !important;}\n </style>\n" + html
}
guard let data = totalString.data(using: String.Encoding.utf8, allowLossyConversion: true) else {
return nil
}
assert(Thread.isMainThread)
guard let attributedText = try? NSAttributedString(data: data, options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue], documentAttributes: nil) else {
return nil
}
let mutable = NSMutableAttributedString(attributedString: attributedText)
if let font = font {
do {
var found = false
mutable.beginEditing()
mutable.enumerateAttribute(NSAttributedString.Key.font, in: NSMakeRange(0, attributedText.length), options: NSAttributedString.EnumerationOptions(rawValue: 0)) { (value, range, stop) in
if let oldFont = value as? UIFont {
let newsize = oldFont.pointSize * 15 * Font.scaleHeruistic / 12
let newFont = oldFont.withSize(newsize)
mutable.addAttribute(NSAttributedString.Key.font, value: newFont, range: range)
found = true
}
}
if !found {
// No font was found - do something else?
}
mutable.endEditing()
// mutable.addAttribute(.font, value: font, range: NSRange(location: 0, length: mutable.length))
}
self.init(attributedString: mutable)
}
}
alternatively you can use the versions this was derived from and set font on UILabel after setting attributedString
this will clobber the size and boldness encapsulated in the attributestring though
kudos for reading through all the answers up to here. You are a very patient man woman or child.
Solution 17 - Iphone
A function to convert html to Attributed NSAttributedString that will adapt dynamic size + adapt accessibility for the text.
static func convertHtml(string: String?) -> NSAttributedString? {
guard let string = string else {return nil}
guard let data = string.data(using: .utf8) else {
return nil
}
do {
let attrStr = try NSAttributedString(data: data,
options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue],
documentAttributes: nil)
let range = NSRange(location: 0, length: attrStr.length)
let str = NSMutableAttributedString(attributedString: attrStr)
str.enumerateAttribute(NSAttributedString.Key.font, in: NSMakeRange(0, str.length), options: .longestEffectiveRangeNotRequired) {
(value, range, stop) in
if let font = value as? UIFont {
let userFont = UIFontDescriptor.preferredFontDescriptor(withTextStyle: .title2)
let pointSize = userFont.withSize(font.pointSize)
let customFont = UIFont.systemFont(ofSize: pointSize.pointSize)
let dynamicText = UIFontMetrics.default.scaledFont(for: customFont)
str.addAttribute(NSAttributedString.Key.font,
value: dynamicText,
range: range)
}
}
str.addAttribute(NSAttributedString.Key.underlineStyle, value: 0, range: range)
return NSAttributedString(attributedString: str.attributedSubstring(from: range))
} catch {}
return nil
}
To use:
let htmToStringText = convertHtml(string: html)
self.bodyTextView.isEditable = false
self.bodyTextView.isAccessibilityElement = true
self.bodyTextView.adjustsFontForContentSizeCategory = true
self.bodyTextView.attributedText = htmToStringText
self.bodyTextView.accessibilityAttributedLabel = htmToStringText