如何为 UIFontMetrics 指定最小 UIContentSizeCategory？

我有一种基于动态类型创建自动缩放字体的方法，如下所示：

extension UIFont {
    public static func getAutoScalingFont(_ fontName: String, _ textStyle: UIFont.TextStyle) -> UIFont {
        // getFontSize pulls from a map of UIFont.TextStyle and UIFont.Weight to determine the appropriate point size
        let size = getFontSize(forTextStyle: textStyle)
        guard let font = UIFont(name: fontName.rawValue, size: size) else { 
            return UIFont.systemFont(ofSize: size)
        }
        let fontMetrics = UIFontMetrics(forTextStyle: textStyle)
        let traitCollection = UITraitCollection(preferredContentSizeCategory: UIApplication.shared.preferredContentSizeCategory)
        let fontDescriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: textStyle, compatibleWith: traitCollection)
        return fontMetrics.scaledFont(for: font, maximumPointSize: fontDescriptor.pointSize)
    }
}

这看起来效果很好；当我更改手机设置中的文本大小滑块值时，字体会根据需要进行缩放。

我现在正在尝试添加逻辑minimumUIContentSizeCategory。也就是说，如果用户将其文本大小值设置为小于我指定的最小大小类别，则字体应按比例缩放，就像他们选择了最小值一样。

这是我的尝试：

extension UIFont {
    // This variable represents the minimum size category I want to support; that is, if the user
    // chooses a size category smaller than .large, fonts should be scaled to the .large size
    private static let minimumSupportedContentSize: UIContentSizeCategory = .large

    public static func getAutoScalingFont(_ fontName: String, _ textStyle: UIFont.TextStyle) -> UIFont {
        let size = getFontSize(forTextStyle: textStyle)
        guard let font = UIFont(name: fontName.rawValue, size: size) else { 
            return UIFont.systemFont(ofSize: size)
        }
        // I've extended UIContentSizeCategory to adhere to Comparable so this works fine
        let contentSize = max(UIApplication.shared.preferredContentSizeCategory, minimumSupportedContentSize)
        let fontMetrics = UIFontMetrics(forTextStyle: textStyle)
        let traitCollection = UITraitCollection(preferredContentSizeCategory: contentSize)
        let fontDescriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: textStyle, compatibleWith: traitCollection)
        return fontMetrics.scaledFont(for: font, maximumPointSize: fontDescriptor.pointSize)
    }
}

通过日志我可以看出，正如预期的那样，contentSize我传递给 UITraitCollection 初始值设定项的值永远不会小于.large。但是，传递给该初始值设定项的值似乎代表一个maximum内容大小类别。也就是说，如果我像这样初始化特征集合：

let traitCollection = UITraitCollection(preferredContentSizeCategory: .large)

对于所有小于 UIContentSizeCategory 的字体，字体将重新缩放.large但不会针对大于的任何类别重新缩放.large.

有谁知道如何完成设置minimumUIContentSizeCategory？

虽然我们有minimumContentSizeCategory and maximumContentSizeCategory从 iOS 15 开始支持，但在某些情况下我们仍然需要旧的方式。例如，当我们需要支持动态文本样式时，这两个属性不起作用NSAttributedString.

这是我用旧方法做的，

Use UIApplication.shared.preferredContentSizeCategory来决定哪个preferredContentSizeCategory与使用UITraitCollection

Example:

func getPreferredFont(textStyle: UIFont.TextStyle, weight: UIFont.Weight? = nil) -> UIFont {
    let preferredContentSizeCategory: UIContentSizeCategory
    switch UIApplication.shared.preferredContentSizeCategory {
    case .extraSmall, .small, .medium:
        preferredContentSizeCategory = .large
    case .accessibilityExtraLarge, .accessibilityExtraExtraLarge, .accessibilityExtraExtraExtraLarge:
        preferredContentSizeCategory =  .accessibilityLarge
    default:
        preferredContentSizeCategory = UIApplication.shared.preferredContentSizeCategory
    }
    let traitCollection = UITraitCollection(preferredContentSizeCategory: preferredContentSizeCategory)
    let fontDescriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: textStyle, compatibleWith: traitCollection)
    let fontMetrics = UIFontMetrics(forTextStyle: textStyle)
    let font: UIFont
    if let weight = weight {
        font = UIFont.systemFont(ofSize: fontDescriptor.pointSize, weight: weight)
    } else {
        font = UIFont.systemFont(ofSize: fontDescriptor.pointSize)
    }
    return fontMetrics.scaledFont(for: font, maximumPointSize: fontDescriptor.pointSize, compatibleWith: traitCollection)
}