Creating an italic version from a *light* font using symbolic traits

Question

I'd like to get an italic version of a light font, for example "HelveticaNeue-Light".

Using a fontDescriptor gives me the italic version of the 'regular' "Helvetica Neue" instead of the italic "HelveticaNeue-Light". I could retrieve the fontDescriptor.fontAttributes and update the UIFontDescriptor.AttributeName.name, but that's tricky, because the naming is different per font ("HelveticaNeue" uses "Italic", Helvetica uses "Oblique").

let lightFont = UIFont(name: "HelveticaNeue-Light", size: 16.0)!
var lightFontDescriptor = lightFont.fontDescriptor.withSymbolicTraits([.traitItalic])!
var lightFontWithItalicTraits = UIFont(descriptor: lightFontDescriptor, size: 0)

// <UICTFont: ..> font-family: "HelveticaNeue-Light"; font-weight: normal; font-style: normal; font-size: 16.00pt
print(lightFont)

// <UICTFont: ..> font-family: "Helvetica Neue"; font-weight: normal; font-style: italic; font-size: 16.00pt
print(lightFontWithItalicTraits)

// The font I expect:
let lightItalicFont = UIFont(name: "HelveticaNeue-LightItalic", size: 16.0)!
// <UICTFont: ..> font-family: "HelveticaNeue-LightItalic"; font-weight: normal; font-style: italic; font-size: 16.00pt
print(lightItalicFont)

Any other idea how to get the italic version of an existing font?

Answer 1

It's not the prettiest, but it's functional. It handles all built-in iOS fonts.

Extension:

extension UIFont {
    func italic() -> UIFont? {
        if let italic = UIFont.init(name: "\(self.fontName)-Italic", size: self.pointSize) {
            return italic
        } else if let italic = UIFont.init(name: "\(self.fontName)Italic", size: self.pointSize) {
            return italic
        }
        if let oblique = UIFont.init(name: "\(self.fontName)-Oblique", size: self.pointSize) {
            return oblique
        } else if let oblique = UIFont.init(name: "\(self.fontName)Oblique", size: self.pointSize) {
            return oblique
        }
        var suffixFontName = self.fontName // for font names that have a 2 letter suffix such as ArialMT
        suffixFontName.removeLast(2)
        let suffix = self.fontName.suffix(2)
        if let suffixFontName = UIFont.init(name: "\(suffixFontName)-Italic\(suffix)", size: self.pointSize) {
            return suffixFontName
        }
        if let suffixFontName = UIFont.init(name: "\(suffixFontName)Italic\(suffix)", size: self.pointSize) {
            return suffixFontName
        }
        // no italic, oblique, or mt italic font found
        return nil
    }
}

Usage:

    let helveticaNeueLightItalic = UIFont(name: "HelveticaNeue-Light", size: 16.0)!.italic()
    print(helveticaNeueLightItalic)

    let helveticaItalic = UIFont(name: "Helvetica", size: 16.0)!.italic()
    print(helveticaItalic)

    let helveticaLightItalic = UIFont(name: "Helvetica-Light", size: 16.0)!.italic()
    print(helveticaLightItalic)

    let arialMtItalic = UIFont(name: "ArialMT", size: 16.0)!.italic()
    print(arialMtItalic)

    let arialMtBoldItalic = UIFont(name: "Arial-BoldMT", size: 16.0)!.italic()
    print(arialMtBoldItalic)