You probably don't need an "extension" as such, if you want this for any custom fonts...
Just add a function (similar to some above) that you can call from anywhere (i.e. without a class) and then you can embolden words within any string, on numerous occasions by calling just ONE LINE of code:
To go in a file like constants.swift:
import Foundation
import UIKit
func addBoldText(fullString: NSString, boldPartOfString: NSString, font: UIFont!, boldFont: UIFont!) -> NSAttributedString {
let nonBoldFontAttribute = [NSFontAttributeName:font!]
let boldFontAttribute = [NSFontAttributeName:boldFont]
let boldString = NSMutableAttributedString(string: fullString as String, attributes:nonBoldFontAttribute)
boldString.addAttributes(boldFontAttribute, range: fullString.rangeOfString(boldPartOfString as String))
return boldString
}
Then you can just call this one line of code for any UILabel:
self.UILabel.attributedText = addBoldText("Check again in 30 DAYS to find more friends", boldPartOfString: "30 DAYS", font: normalFont!, boldFont: boldSearchFont!)
//Mark: Albeit that you've had to define these somewhere:
let normalFont = UIFont(name: "INSERT FONT NAME", size: 15)
let boldFont = UIFont(name: "INSERT BOLD FONT", size: 15)