Swift make UILabel text bold in between custom identifier

I have a UILabel with a text of

This is not bold, -bold- this is bold, -/bold- and this is another not bold, -bold- this is another bold -/bold-.

now, I want to change the font of the text in between every -bold- and -/bold- in text to bold so it will become something like this

This is not bold, this is bold, and this is another not bold, this is another bold.

How can I do that?

First, get the strings within the delimiter.

let query = "This is not bold, -bold- this is bold, -/bold- and this is another not bold, -bold- this is another bold -/bold-"
let regex = try! NSRegularExpression(pattern: "-bold- (.*?) -/bold-", options: [])
var results = [String]()
regex.enumerateMatches(in: query, options: [], range: NSMakeRange(0, query.utf16.count)) { result, flags, stop in

    if let r = result?.range(at: 1),
        let range = Range(r, in: query) {
        results.append(String(query[range]))
    }
}

print(results)

Next, Create a string extension method like below.

extension String {

    func attributedString(with style: [NSAttributedString.Key: Any]? = nil,
                          and highlightedTextArray: [String],
                          with highlightedTextStyleArray: [[NSAttributedString.Key: Any]?]) -> NSAttributedString {

        let formattedString = NSMutableAttributedString(string: self, attributes: style)
        if highlightedTextArray.count != highlightedTextStyleArray.count {
            return formattedString
        }

        for (highlightedText, highlightedTextStyle) in zip(highlightedTextArray, highlightedTextStyleArray) {
            let highlightedTextRange: NSRange = (self as NSString).range(of: highlightedText as String)
            formattedString.setAttributes(highlightedTextStyle, range: highlightedTextRange)
        }

        return formattedString
    }
}

Method details:

• first argument: Font style and other attributes to be applied for complete string.
• second argument: Array of strings for which new style to be applied.
• third argument: New Style (in this case, Bold) to be applied.
• returns resultant attributed string.

Finally, call the method as below.

let attributedText = query.attributedString(with: [.font: UIFont.systemFont(ofSize: 12.0, weight: .regular)],
                       and: results,
                       with: [[.font: UIFont.systemFont(ofSize: 12.0, weight: .bold)]])

Hope it helps.