NSAttributedString与UIFontWeightTraits

Question

我正在尝试生成一个基本上只有默认字体、斜体和不同文本颜色的NSAttributedString。到目前为止很简单。

现在，我希望整个字符串的不同子字符串更加粗体。基本上应该是这样的：

从约翰史密斯 25.08。8:00

(只是颜色不同。)

看起来我把字典搞错了，我把它传递给了NSMutableAttributedString的addAttributes(_:_:)函数。从文档，我知道这本字典应该是这样的：

[UIFontDescriptorTraitsAttribute: 
    [UIFontWeightTrait: NSNumber(double: Double(UIFontWeightBold))]

但这似乎行不通。我最后得到的只是字符串的斜体版本。很明显我搞错了。有什么想法吗？

更新:添加简单示例

// Preparation
let rawString = "from John Smith on 25.08. at 8:00"
let attributedString = NSMutableAttributedString(string: rawString)
let nameRange = (rawString as NSString).rangeOfString("John Smith")
let italicFont = UIFont.italicSystemFontOfSize(14)

// Make entire string italic: works!
attributedString.addAttributes([NSFontAttributeName : italicFont], range: NSMakeRange(0, 33))
// Make the name string additionally bold: doesn't work!
attributedString.addAttributes([UIFontDescriptorTraitsAttribute:
        [UIFontWeightTrait: NSNumber(double: Double(UIFontWeightBold))]], range: nameRange)

// Show it on the label
attributedStringLabel.attributedText = attributedString

谢谢!

Answer 1

UIFontDescriptorTraitsAttribute在NSAttributedString属性字典中不是一个可识别的键，因此获得了重建UIFont和使用NSFontAttributeName键所需的特征。

    //prepare the fonts. we derive the bold-italic font from the italic font
    let italicFont = UIFont.italicSystemFontOfSize(14)
    let italicDesc = italicFont.fontDescriptor()
    let italicTraits  = italicDesc.symbolicTraits.rawValue
    let boldTrait = UIFontDescriptorSymbolicTraits.TraitBold.rawValue
    let boldItalicTraits = UIFontDescriptorSymbolicTraits(rawValue:italicTraits | boldTrait)
    let boldItalicDescriptor = italicDesc.fontDescriptorWithSymbolicTraits(boldItalicTraits)
    let boldItalicFont = UIFont(descriptor: boldItalicDescriptor, size: 0.0)

    //prepare the string
    let rawString = "from John Smith on 25.08. at 8:00"
    let attributedString = NSMutableAttributedString(string: rawString)

    let fullRange = NSMakeRange(0, 33)
    let nameRange = (rawString as NSString).rangeOfString("John Smith")

    attributedString.addAttributes([NSFontAttributeName:italicFont], range: fullRange)
    attributedString.addAttributes([NSFontAttributeName:boldItalicFont], range: nameRange)

另见：NSAttributedString:设置FontAttributes不会更改字体