ios swift: Is it possible to change the font style of a certain word in a string?

NSMutableAttributedString.

You create an NSMutableAttributedString and apply the effects you'd like with addAttributes:range.

Then assign it to the attributedText property of your UILabel.

If you already know the longest word you have to get the range of that word in the string. I prefer the NSString method rangeOfString: for this.

You then create a NSMutableAttributedString from the string, with your default attributes. Finally you apply highlighting attributes to the range you figured out earlier.

let longString = "Lorem ipsum dolor. VeryLongWord ipsum foobar"
let longestWord = "VeryLongWord"

let longestWordRange = (longString as NSString).rangeOfString(longestWord)

let attributedString = NSMutableAttributedString(string: longString, attributes: [NSFontAttributeName : UIFont.systemFontOfSize(20)])

attributedString.setAttributes([NSFontAttributeName : UIFont.boldSystemFontOfSize(20), NSForegroundColorAttributeName : UIColor.redColor()], range: longestWordRange)


label.attributedText = attributedString

Update for Swift 5.0

let longestWordRange = (longString as NSString).range(of: longestWord)

let attributedString = NSMutableAttributedString(string: longString, attributes: [NSAttributedStringKey.font : UIFont.systemFont(ofSize: 20)])

attributedString.setAttributes([NSAttributedStringKey.font : UIFont.boldSystemFont(ofSize: 20), NSAttributedStringKey.foregroundColor : UIColor.red], range: longestWordRange)

Which looks like this in my playground:

You want to look at Attributed Strings and NSRange. You can use both of these together to create different styles for ranges in the string. Here is a snippet:

myMutableString = NSMutableAttributedString(string: myString, attributes: [NSFontAttributeName:UIFont(name: "Georgia", size: 18.0)!])

//Add more attributes here:
myMutableString.addAttribute(NSFontAttributeName, value: UIFont(name: "Chalkduster", size: 24.0), range: NSRange(location: 7,length: 5))
myMutableString.addAttribute(NSFontAttributeName, value: UIFont(name: "AmericanTypewriter-Bold", size: 18.0)!, range: NSRange(location:2,length:4))
myMutableString.addAttribute(NSForegroundColorAttributeName, value: UIColor.redColor(), range: NSRange(location:2,length:4))

myMutableString.addAttribute(NSFontAttributeName, value: UIFont(name: "Georgia", size: 36.0)!, range: NSRange(location: 0, length: 1))
myMutableString.addAttribute(NSStrokeColorAttributeName, value: UIColor.blueColor(), range:  NSRange(location: 0, length: 1))
myMutableString.addAttribute(NSStrokeWidthAttributeName, value: 2, range: NSRange(location: 0, length: 1))

myMutableString.addAttribute(NSBackgroundColorAttributeName, value: UIColor.greenColor(), range: NSRange(location: 0, length: myString.length))
myLabel.backgroundColor = UIColor.grayColor()

//Apply to the label
myLabel.attributedText = myMutableString