System font for both iOS 8 and iOS 9

Question

I want to support both iOS 8 and iOS 9 systems for my app. And maybe iOS 7. As we know, system font for iOS 7 and 8 is Helvetica Neue. But in iOS 9 system font is San-Francisco. And if you don't set Helvetica font explicitly via [UIFont fontWithName:@"HelveticaNeue" size:15];, but use [UIFont systemFontOfSize:15];, you'll get Helvetica for iOS 7 and 8 and San-Francisco for iOS 9 automatically. And it's great! For interface builder's labels and buttons you can set thin, ultra thin, medium etc. system fonts. It is great too. But how can I set these thin, ultra, medium system fonts in code, programmatically? Do I need to create a category with a fork for iOS 9 and previous iOS?

Answer 1

I've created this extension:

import Foundation
import UIKit

enum SystemFontWeight : String {
    case UltraLight = "HelveticaNeue-UltraLight"
    case Thin = "HelveticaNeue-Thin"
    case Light = "HelveticaNeue-Light"
    case Regular = "HelveticaNeue"
    case Medium = "HelveticaNeue-Medium"
    case Semibold = "Helvetica-Bold"
    case Bold = "HelveticaNeue-Bold"
    case Heavy = "HelveticaNeue-CondensedBold"
    case Black = "HelveticaNeue-CondensedBlack"

    var weightValue:CGFloat? {
        if #available(iOS 8.2, *) {
            switch self {
            case .UltraLight:
                return UIFontWeightUltraLight
            case .Thin:
                return UIFontWeightThin
            case .Light:
                return UIFontWeightLight
            case .Regular:
                return UIFontWeightRegular
            case .Medium:
                return UIFontWeightMedium
            case .Semibold:
                return UIFontWeightSemibold
            case .Bold:
                return UIFontWeightBold
            case .Heavy:
                return UIFontWeightHeavy
            case .Black:
                return UIFontWeightBlack
            }
        } else {
            return nil
        }
    }
}

extension UIFont {
    static func systemFontOfSize(fontSize:CGFloat, weight:SystemFontWeight) -> UIFont {
        if #available(iOS 8.2, *) {
            return UIFont.systemFontOfSize(fontSize, weight: weight.weightValue!)

        } else {
            // Fallback on earlier versions
            return UIFont(name: weight.rawValue, size: fontSize)!
        }
    }
}

Which makes it possible to apply font like this:

myLabel.font = UIFont.systemFontOfSize(14, weight: .Medium)

This will automatically set the correct font for both iOS 8 and iOS 9.

Answer 2

Use + systemFontOfSize:weight:. It's available for iOS 8 and above.

For iOS 7, interface builder settings will work, and for code you will need to create a UIFontDescriptor with the appropriate weight.