无法在iOS 13上创建小Caps选择器

Question

下面的代码使我能够在iOS 12上创建大写文本，但是在iOS 13上，它停止工作了。

iOS 12日志

.SFUIDisplay-Semibold
.SFUIDisplay-Semibold

iOS 13测井

.SFUI-Semibold
TimesNewRomanPSMT

看起来SFUI字体至少在iOS 13中已经更改了名称，但是它是否也放弃了对小盘的支持？

let font = UIFont.systemFont(ofSize: 20, weight: .semibold)
print(font.fontName)

let settings = [[UIFontDescriptor.FeatureKey.featureIdentifier: kLowerCaseType,
                 UIFontDescriptor.FeatureKey.typeIdentifier: kLowerCaseSmallCapsSelector]]

let attributes: [UIFontDescriptor.AttributeName: AnyObject] = [UIFontDescriptor.AttributeName.featureSettings: settings as AnyObject,
                                                               UIFontDescriptor.AttributeName.name: font.fontName as AnyObject]

let smallCapsFont = UIFont(descriptor: UIFontDescriptor(fontAttributes: attributes), size: 20)
print(smallCapsFont.fontName)

Answer 1

你的代码总是错的。您首先创建一个字体，然后通过传递字体的名称从它派生一个字体描述符

let font = UIFont.systemFont(ofSize: 20, weight: .semibold)
let settings = [
    [UIFontDescriptor.FeatureKey.featureIdentifier: kLowerCaseType,
    UIFontDescriptor.FeatureKey.typeIdentifier: kLowerCaseSmallCapsSelector]
]
let attributes: [UIFontDescriptor.AttributeName: AnyObject] = [
    UIFontDescriptor.AttributeName.featureSettings: settings as AnyObject,
    UIFontDescriptor.AttributeName.name: font.fontName as AnyObject // ** NO!
]
let smallCapsFont = UIFont(descriptor: UIFontDescriptor(fontAttributes: attributes), size: 20)

那从来都不是正确的。您应该直接从字体本身派生字体描述符。这就是您的代码应该始终看起来的样子。它在iOS 12中工作，现在起作用了：

let font = UIFont.systemFont(ofSize: 20, weight: .semibold)
let settings = [
    [UIFontDescriptor.FeatureKey.featureIdentifier: kLowerCaseType,
    UIFontDescriptor.FeatureKey.typeIdentifier: kLowerCaseSmallCapsSelector]
]
let desc = font.fontDescriptor.addingAttributes([.featureSettings:settings])
let smallCapsFont = UIFont(descriptor: desc, size: 0)

Answer 2

像这样的系统字体现在可以使用“点”/ .符号(即使像font.fontName示例一样重新创建它们)来进行更长的引用，如下所示：

https://developer.apple.com/videos/play/wwdc2019/227/

从iOS 13开始，您可以使用新的枚举UIFontDescriptor.SystemDesign，使用regular、rounded、serif或monospaced。

关于如何在Swift中使用描述符创建字体的示例(请参阅我如何使用design参数)：

extension UIFont {

    convenience init?(
        style: UIFont.TextStyle,
        weight: UIFont.Weight = .regular,
        design: UIFontDescriptor.SystemDesign = .default) {

        guard let descriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: style)
            .addingAttributes([UIFontDescriptor.AttributeName.traits: [UIFontDescriptor.TraitKey.weight: weight]])
            .withDesign(design) else {
                return nil
        }
        self.init(descriptor: descriptor, size: 0)
    }
}

Answer 3

从@Ash Camerons的答案中汲取灵感，下面是更新的代码，它允许您应用小盘

注意，这只在iOS 13+中有效，但是您可以为iOS 13和更高版本添加.withDesign(systemDesign)行。

let pointSize: CGFloat = 20
let weight: UIFont.Weight = .semibold
let systemDesign: UIFontDescriptor.SystemDesign = .default

let settings = [[UIFontDescriptor.FeatureKey.featureIdentifier: kLowerCaseType,
                 UIFontDescriptor.FeatureKey.typeIdentifier: kLowerCaseSmallCapsSelector]]

let descriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: .callout)
        .addingAttributes([UIFontDescriptor.AttributeName.traits: [UIFontDescriptor.TraitKey.weight: weight]])
        .addingAttributes([UIFontDescriptor.AttributeName.featureSettings: settings])
        .addingAttributes([UIFontDescriptor.AttributeName.size: pointSize])
        .withDesign(systemDesign)

let font = UIFont(descriptor: descriptor!, size: pointSize)