UIFont+Util.swift

import UIKit

extension UIFont {
    /// Returns an instance of the system font for the specified text style and weight.
    ///
    /// The scale of the text style is determined by the specified traits.
    ///
    /// If no traits are specified (the default) the font will be scaled for the user's selected content size category,
    ///
    /// Otherwise the font will be scaled using the content size category information in the specified trait collection.
    ///
    /// - Parameters:
    ///   - style: The text style for which to return a font. See "Text Styles" in `UIFontDescriptor` for recognized values.
    ///   - traitCollection: The trait collection containing the content size category information.
    ///   - weight: The weight of the font, specified as a weight constant. For possible values see "Font Weights" in `UIFontDescriptor`.
    /// - Returns: The system font associated with the specified text style with the specified weight.
    class func preferredFont(forTextStyle style: TextStyle,
                             compatibleWith traitCollection: UITraitCollection? = nil,
                             weight: Weight) -> UIFont {
        let descriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: style, compatibleWith: traitCollection)
        let systemFont = UIFont.systemFont(ofSize: descriptor.pointSize, weight: weight)
        let metrics = UIFontMetrics(forTextStyle: style)
        return metrics.scaledFont(for: systemFont, compatibleWith: traitCollection)
    }
}