Change color of text on parts of UILabel that are surrounded by asterisks

Question

I have a string such as the following:

let myString = "This is my *awesome* label which *should* change color";

What I need to do is add this text to a UILabel, changing the text color to orange where the parts of the text are surrounded by asterisks, and removing the asterisks before displaying.

How can I accomplish this?

I know you can combine different colors of text using attributed text for labels, but not sure how to break up the string to achieve the desired behavior.

Answer 1

You could use a regular expression:

let regex = try! NSRegularExpression(pattern: "[\\*]{1}[^\\*]+[\\*]{1}")

regex is a regular expression that matches:

• One asterisk: [\\\\*]{1} . Followed by,
• One or more characters that are not an asterisk: [^\\\\*]+ . Followed by,
• One asterisk: [\\\\*]{1}

Let's get the matches:

let str = "This is my *awesome* label which *should* change color"
let length = (str as NSString).length
let rg = NSRange(location: 0, length: length)
let matches = regex.matches(in: str, range: rg)
let ranges = matches.map {$0.range}

Let's create a mutable attributed string:

let attributedString = NSMutableAttributedString(string: str)

And add the foregroundColor attribute to the matches, and remove the asterisks:

let attribute = [NSAttributedString.Key.foregroundColor: UIColor.orange]
let startIndex = str.startIndex
ranges.reversed()
    .forEach{ range in
        attributedString.addAttributes(attribute, range: range)
        let start = str.index(startIndex, offsetBy: range.lowerBound.advanced(by: 1))
        let end = str.index(startIndex, offsetBy: range.upperBound.advanced(by: -1))
        let withoutAsterisk = String(str[start..<end])
        attributedString.replaceCharacters(in: range, with: withoutAsterisk)
}

And set the attributedText of your label

label.attributedText = attributedString