为 Swift 中的 iOS 字体描述符添加自定义粗细

Question

这看起来应该很简单，但无论出于何种原因，它都不起作用。我在 SO 上读过类似的帖子，看起来 Font Traits 字典可能有问题？这是一个问题还是我完全错过了什么？这是我第一次弄乱这样的字体，所以我认为它可能是后者。

我不想使用常量或提供带有“-bold”变体的字体。我想对字体粗细进行精细控制。

let traits = [UIFontWeightTrait : 1.0]
imgFontDescriptor = UIFontDescriptor(fontAttributes: [UIFontDescriptorNameAttribute: "Helvetica"])
imgFontDescriptor = imgFontDescriptor.fontDescriptorByAddingAttributes([UIFontDescriptorTraitsAttribute:traits])
imgTextFont = UIFont(descriptor: imgFontDescriptor!, size: 24.0)

研究：

Font Descriptor returns nil in iOS 8
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIFontDescriptor_Class/#//apple_ref/doc/constant_group/Font_Traits_Dictionary_Keys

根据 iOS 文档，使用数值应该可行（我是运行 iOS 9.2）：

UIFontWeightTrait

The normalized weight value as an NSNumber object. The valid value range is from -1.0 to 1.0. The value of 0.0 corresponds to the regular or medium font weight. You can also use a font weight constant to specify a particular weight; for a list of constants you can use, see Font Weights. Available in iOS 7.0 and later.

Answer 1

UIFont(descriptor: imgFontDescriptor!, size: 24.0) 是 returning 一个与描述符匹配的字体。如果它找不到与您的描述相匹配的字体，它将 return 设为默认字体。因此，您无法手动控制体重。这取决于您使用的字体。如果字体支持该重量，它将 return 那个。

还有一件事，你应该使用[UIFontDescriptorFamilyAttribute: "Helvetica"]。因此它将根据 FamilyName 和您的 FontWeight 确定 FontName。

正确的方法是使用 Apple 库中的常量：

public let UIFontWeightUltraLight: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightThin: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightLight: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightRegular: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightMedium: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightSemibold: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightBold: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightHeavy: CGFloat
@available(iOS 8.2, *)
public let UIFontWeightBlack: CGFloat*/

您应该使用 http://iosfonts.com/ 来确定该姓氏支持的字体粗细。

如果是 Helvetica：

let traits = [UIFontWeightTrait: UIFontWeightLight] // UIFontWeightBold / UIFontWeightRegular
let imgFontDescriptor = UIFontDescriptor(fontAttributes: [UIFontDescriptorFamilyAttribute: "Helvetica"])
imgFontDescriptor = imgFontDescriptor.fontDescriptorByAddingAttributes([UIFontDescriptorTraitsAttribute: traits])

Answer 2

如果您使用现有的 fontDescriptor（例如来自现有的字体），它可能无法工作，因为 fontDescriptor.fontAttributes.

中显式的“.name”属性

解决方案，对我有用 (Swift 4)：

extension UIFont {
    var bold: UIFont { return withWeight(.bold) }
    var semibold: UIFont { return withWeight(.semibold) }

    private func withWeight(_ weight: UIFont.Weight) -> UIFont {
        var attributes = fontDescriptor.fontAttributes
        var traits = (attributes[.traits] as? [UIFontDescriptor.TraitKey: Any]) ?? [:]

        traits[.weight] = weight

        attributes[.name] = nil
        attributes[.traits] = traits
        attributes[.family] = familyName

        let descriptor = UIFontDescriptor(fontAttributes: attributes)

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

用法：

let baseFont = UIFont(name: "American Typewriter", size: 20)!
let boldFont = baseFont.bold
let semibold = baseFont.semibold

Answer 3

使用 Swift 4.1，只需执行如下操作：

var descriptor = UIFontDescriptor(name: "Helvetica Neue", size: 24.0)
descriptor = descriptor.addingAttributes([UIFontDescriptor.AttributeName.traits : [UIFontDescriptor.TraitKey.weight : UIFont.Weight.light]])
let font = UIFont(descriptor: descriptor, size: 24.0)

Answer 4

一个简洁的扩展：

extension UIFont {
  /// Returns a new font with the weight specified
  /// - Parameter weight: The new font weight
  func withWeight(_ weight: UIFont.Weight) -> UIFont {
    let newDescriptor = fontDescriptor.addingAttributes([.traits: [
      UIFontDescriptor.TraitKey.weight: weight]
    ])
    return UIFont(descriptor: newDescriptor, size: pointSize)
  }
}

Answer 5

这是 Apple 在他们的 CareKit 框架中 UIFont+Extensions.swift 的扩展：

https://github.com/carekit-apple/CareKit/

extension UIFont {
    static func preferredCustomFont(forTextStyle textStyle: TextStyle, weight: Weight) -> UIFont {
        let defaultDescriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: textStyle)
        let size = defaultDescriptor.pointSize
        let fontDescriptor = UIFontDescriptor(fontAttributes: [
            UIFontDescriptor.AttributeName.size: size,
            UIFontDescriptor.AttributeName.family: UIFont.systemFont(ofSize: size).familyName
        ])

        // Add the font weight to the descriptor
        let weightedFontDescriptor = fontDescriptor.addingAttributes([
            UIFontDescriptor.AttributeName.traits: [
                UIFontDescriptor.TraitKey.weight: weight
            ]
        ])
        return UIFont(descriptor: weightedFontDescriptor, size: 0)
    }
}

为 Swift 中的 iOS 字体描述符添加自定义粗细

Add custom weight to iOS Font descriptor in Swift

fonts

ios

swift

uifontdescriptor