ios - UIFont 等宽数字+小型大写字母

Question

我正在尝试创建一个 UIFont具有以下属性:

• 大写小写
• 小写小型大写字母
• 等宽数字

我正在使用系统字体 ( San Francisco )，它支持所有这些功能。
据我所知，唯一的方法是使用多个 UIFontDescriptor .

这是我正在使用的代码:

extension UIFont {

    var withSmallCaps: UIFont {
        let upperCaseFeature = [
            UIFontDescriptor.FeatureKey.featureIdentifier : kUpperCaseType,
            UIFontDescriptor.FeatureKey.typeIdentifier : kUpperCaseSmallCapsSelector
        ]
        let lowerCaseFeature = [
            UIFontDescriptor.FeatureKey.featureIdentifier : kLowerCaseType,
            UIFontDescriptor.FeatureKey.typeIdentifier : kLowerCaseSmallCapsSelector
        ]
        let features = [upperCaseFeature, lowerCaseFeature]
        let smallCapsDescriptor = self.fontDescriptor.addingAttributes([UIFontDescriptor.AttributeName.featureSettings : features])

        return UIFont(descriptor: smallCapsDescriptor, size: pointSize)
    }

    var withMonospacedDigits: UIFont {
        let monospacedDigitsFeature = [
            UIFontDescriptor.FeatureKey.featureIdentifier : kNumberSpacingType,
            UIFontDescriptor.FeatureKey.typeIdentifier : kMonospacedNumbersSelector
        ]
        let monospacedDigitsDescriptor = self.fontDescriptor.addingAttributes([UIFontDescriptor.AttributeName.featureSettings : [monospacedDigitsFeature]])

        return UIFont(descriptor: monospacedDigitsDescriptor, size: pointSize)
    }
}

我应该能够通过这行代码获得具有前面提到的所有特征的字体:

let font = UIFont.systemFont(ofSize: 16, weight: .regular).withSmallCaps.withMonospacedDigits
// OR
let font = UIFont.monospacedDigitSystemFont(ofSize: 16, weight: .regular).withSmallCaps

但由于某些原因，它不起作用。我无法让字体在具有等宽数字的同时具有小型大写字母。

我做错了什么？

Answer 1

多亏了reference document，我明白了为什么它不起作用。链接为 @Carpsen90 .

似乎数字间距功能是独有的。

如文档中所述:

Features are classified as "exclusive" and "nonexclusive." This indicates whether several different selectors within a given feature type may be selected at once. Thus, it is possible to have both common and rare ligatures turned on, whereas it is impossible to display a given fraction as simultaneously vertical and diagonal.

因此同时拥有等宽数字+小型大写字母功能是不可能的。

<小时/>

编辑:

我看错了文档。该功能的选择器是排他的。但不是全部功能。所以应该是可以的。