Set Specific Font Weight for UILabel in Swift

You can use this extension. It assigns the weight to the fontDescriptor's weight key and instantiate your font with this new descriptor.

extension UIFont {
  func withWeight(_ weight: UIFont.Weight) -> UIFont {
    let newDescriptor = fontDescriptor.addingAttributes([.traits: [
      UIFontDescriptor.TraitKey.weight: weight]
    ])
    return UIFont(descriptor: newDescriptor, size: pointSize)
  }
}

I couldn't get the UIFontDescriptor to work with the font weight trait but there is another approach.

let font = UIFont.systemFont(ofSize: 20, weight: .light)

Replace .light with whichever value you want from UIFont.Weight which basically matches the dropdown list shown in your question.

The very old thread, but someone may be interested in how to do it in Swift.

UIFont.Weight defines all of the options:

• ultraLight
• thin
• light
• regular
• medium
• semibold
• bold
• heavy
• black

you can use simply like that, e.g.:

label.font = UIFont.systemFont(ofSize: size, weight: .bold)

or if you want to keep the previous size:

label.font = UIFont.systemFont(ofSize: label.font!.pointSize, weight: .bold)