UIFont：如何使用文体替代字符？

Question

在我的应用程序中，我想将 stylistic alternate font 用于 'a' 而不是 system font。

附上screenshot，解释字体的不同渲染。

如何为 UILabel 和 UITextView 启用此行为，以便它呈现正确的 One Storey 'a'？

我确实找到了 YouTube video link ，它解释了这一点，但他使用的是 custom font 并且它是硬编码的。我只想使用system font，但要使用这个替代字符。

我也许可以用custom character 硬编码UILabel，我不确定，因为我想使用System font。我不想使用custom Font。可编辑的UITextView 怎么样？我们如何让它在用户输入时使用备用a？

Answer 1

这是一个名为“Alternative Stylistic Sets”的字体功能，您可以使用 CoreText 进行配置。请记住，并非所有字体都有此选项，但系统字体有。但是，您需要弄清楚您想要哪个替代设置。

首先，创建你感兴趣的字体：

import CoreText
import UIKit

let baseFont = UIFont.systemFont(ofSize: 72)

然后打印出它的特征：

print(CTFontCopyFeatures(baseFont)!)

找到关于替代风格集的部分，特别是您想要的集，“一层楼：”

    {
    CTFeatureTypeIdentifier = 35;
    CTFeatureTypeName = "Alternative Stylistic Sets";
    CTFeatureTypeSelectors =         (
                    {
            CTFeatureSelectorIdentifier = 2;
            CTFeatureSelectorName = "Straight-sided six and nine";
        },
                    {
            CTFeatureSelectorIdentifier = 4;
            CTFeatureSelectorName = "Open four";
        },
                    {
            CTFeatureSelectorIdentifier = 6;
            CTFeatureSelectorName = "Vertically centered colon";
        },
                    {
            CTFeatureSelectorIdentifier = 10;
            CTFeatureSelectorName = "Vertically compact forms";
        },
                    {
            CTFeatureSelectorIdentifier = 12;
            CTFeatureSelectorName = "High legibility";
        },
                    {
            CTFeatureSelectorIdentifier = 14;
            CTFeatureSelectorName = "One storey a";
        },
        ...

重要的数字是选择器（CTFeatureSelectorIdentifier），14。用它你可以创建一个新的字体描述符和新字体：

let descriptor = CTFontDescriptorCreateCopyWithFeature(
    baseFont.fontDescriptor,
    kStylisticAlternativesType as CFNumber,
    14 as CFNumber)

如果更方便的话，你也可以直接在 UIKit 中执行此操作：

let settings: [UIFontDescriptor.FeatureKey: Int] = [
    .featureIdentifier: kStylisticAlternativesType,
    .typeIdentifier: 14
]

let descriptor = baseFont.fontDescriptor.addingAttributes([.featureSettings: [settings]])

（请注意，.featureIdentifier 是“CTFeatureTypeIdentifier”而.typeIdentifier 是“CTFeatureSelectorIdentifier”，这有点令人惊讶。）

然后你可以创建一个新字体（零大小意味着保持大小不变​​）：

let font = UIFont(descriptor: descriptor, size: 0)

您可以在任何接受 UIFont 的地方使用它。

Answer 2

假设您知道它的名称，下面是一个扩展，可简化为字体选择替代样式集的过程：

示例用法：

guard let updatedFont = font.withAlternativeStylisticSet(withName: "Alternate y") else {
    fatalError("Alternative stylistic set is undefined")
}

UIFont 扩展：

import UIKit
import CoreText

extension UIFont {
    
    /// Returns the font, applying an alternative stylistic style set.
    func withAlternativeStylisticSet(withName name: String) -> UIFont? {
        guard let identifier = alternativeStylisticSetIdentifier(withName: name) else {
            return nil
        }
        
        let settings: [UIFontDescriptor.FeatureKey: Int] = [
            .featureIdentifier: kStylisticAlternativesType,
            .typeIdentifier: identifier
        ]
        
        let fontDescriptor = self.fontDescriptor.addingAttributes([.featureSettings: [settings]])
        return UIFont(descriptor: fontDescriptor, size: 0)
    }
    
    /// Returns the identifier for an alternative stylistic set
    private func alternativeStylisticSetIdentifier(withName selectorName: String) -> Int? {
        guard let ctFeatures = CTFontCopyFeatures(self) else {
            return nil
        }
        
        let features = ctFeatures as [AnyObject] as NSArray
        for feature in features {
            if let featureDict = feature as? [String: Any] {
                if let typeName = featureDict[kCTFontFeatureTypeNameKey as String] as? String {
                    if typeName == "Alternative Stylistic Sets" {
                        if let featureTypeSelectors = featureDict[kCTFontFeatureTypeSelectorsKey as String] as? NSArray {
                            for featureTypeSelector in featureTypeSelectors {
                                if let featureTypeSelectorDict = featureTypeSelector as? [String: Any] {
                                    if let name = featureTypeSelectorDict[kCTFontFeatureSelectorNameKey as String] as? String, let identifier = featureTypeSelectorDict[kCTFontFeatureSelectorIdentifierKey as String] as? Int {
                                        if name == selectorName {
                                            return identifier
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        
        return nil
    }

}