iOS Swift为字体描述符添加自定义权重

这似乎应该是基本上容易的,但无论出于何种原因,它都无法正常工作.我在SO上看过类似的帖子,看起来Font Traits字典可能存在问题？这是一个问题还是我完全错过了什么？这是我第一次搞乱这样的字体,所以我认为可能是后者.

我不想使用常量或提供带有"-bold"变体的字体.我想对字体重量进行细粒度控制.

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

研究:

字体描述符在iOS 8中返回nil

https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIFontDescriptor_Class/#//apple_ref/doc/constant_group/Font_Traits_Dictionary_Keys

根据iOS文档使用数值应该工作(我正在运行iOS 9.2):

UIFontWeightTrait作为NSNumber对象的标准化权重值.有效值范围为-1.0到1.0.值0.0对应于常规或中等字体粗细.您还可以使用字体粗细常量来指定特定的权重; 有关可以使用的常量列表,请参阅字体权重.适用于iOS 7.0及更高版本.

UIFont(descriptor: imgFontDescriptor!, size: 24.0)返回与描述符匹配的Font.如果找不到与您的描述匹配的Font,则返回默认字体.因此,您无法手动控制体重.这取决于您使用的字体.如果Font支持该权重,它将返回该权重.

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 lib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/来确定该系列名称支持的字体粗细.

如果是Helvetica:

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

如果使用现有的fontDescriptor（例如，来自现有字体的字体），则由于fontDescriptor.fontAttributes中的显式“ .name”属性，它可能无法工作。

解决方案，对我有用（快速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

使用Swift 4.1,只需执行以下操作:

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)