Для Swift 4 , Swift 4.2: та Swift 5
let htmlString = """
<html>
<head>
<style>
body {
background-color : rgb(230, 230, 230);
font-family : 'Arial';
text-decoration : none;
}
</style>
</head>
<body>
<h1>A title</h1>
<p>A paragraph</p>
<b>bold text</b>
</body>
</html>
"""
let htmlData = NSString(string: htmlString).data(using: String.Encoding.unicode.rawValue)
let options = [NSAttributedString.DocumentReadingOptionKey.documentType: NSAttributedString.DocumentType.html]
let attributedString = try! NSAttributedString(data: htmlData!, options: options, documentAttributes: nil)
textView.attributedText = attributedString
Для Swift 3 :
let htmlString = """
<html>
<head>
<style>
body {
background-color : rgb(230, 230, 230);
font-family : 'Arial';
text-decoration : none;
}
</style>
</head>
<body>
<h1>A title</h1>
<p>A paragraph</p>
<b>bold text</b>
</body>
</html>
"""
let htmlData = NSString(string: htmlString).data(using: String.Encoding.unicode.rawValue)
let attributedString = try! NSAttributedString(data: htmlData!, options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType], documentAttributes: nil)
textView.attributedText = attributedString