article-customfonts5.swift

class WeightAdheringLabel: UILabel {
    private var originalFont: UIFont?

    override var font: UIFont! {
        set {
            self.originalFont = newValue
            if traitCollection.legibilityWeight == .bold {
                super.font = newValue.fontDescriptor.withSymbolicTraits(.traitBold).map { UIFont(descriptor: $0, size: newValue.pointSize) } ?? newValue
            } else {
                super.font = newValue
            }
        }
        get {
            return super.font
        }
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        if traitCollection.legibilityWeight == .bold && previousTraitCollection?.legibilityWeight != .bold {
            super.font = originalFont?.fontDescriptor.withSymbolicTraits(.traitBold).map { UIFont(descriptor: $0, size: 0) } ?? font
        } else if traitCollection.legibilityWeight == .regular && previousTraitCollection?.legibilityWeight != .regular {
            super.font = originalFont ?? font
        }
    }
}