Swift：UILabel超出宽度文字的截取

JKSwiftExtension，测试用例在 JKContentSizeViewController.swift 里面
需求：单行文字可缩放到一定比例，按照Char截取，超出截掉，不允许出现Char被截取一半的情况

效果图

一、常规的剪切方式 (lineBreakMode 设置文字过长时的显示格式)

• 1.1、NSLineBreakMode枚举如下

  public enum NSLineBreakMode : Int {
     //  以单词为显示单位显=示，后面部分省略不显示
     case byWordWrapping = 0 
     // 以字符为显示单位显示，后面部分省略不显示。
     case byCharWrapping = 1 
     // 剪切与文本宽度相同的内容长度，后半部分被删除。
     case byClipping = 2 
     // 前面部分文字以……方式省略，显示尾部文字内容
     case byTruncatingHead = 3 
     // 结尾部分的内容以……方式省略，显示头的文字内容
     case byTruncatingTail = 4 
     // 中间的内容以……方式省略，显示头尾的文字内容
     case byTruncatingMiddle = 5 
  }
  

  使用如下：以 byWordWrapping 的形式剪切

  let label = UILabel(frame: CGRect(x: 20, y: 20, width: 100, height: 19))
  label.backgroundColor = .yellow
  label.font = UIFont.systemFont(ofSize: 10)
  label.textAlignment = .left
  label.textColor = UIColor.brown
  label.lineBreakMode = .byWordWrapping
  return label
  

二、本次的需求实现

• 2.1、需求：单行文字可缩放到一定比例，按照Char截取，超出截掉，不允许出现Char被截取一半的情况

  • 需求分析：可缩放一定比例、按照Char截取、不允许出现Char被截取一半的情况
  • 实现方式：先获取缩放后的字体大小，后获取指定宽度的第一行文字的内容

• 2.2、具体的核心代码如下

  public struct JKContentSize {}
  
  public extension JKContentSize {
      // MARK: 2.1、行数和每行的内容
      /// 获取已知 width 的 label 的文本行数 & 每一行内容
      /// - Parameters:
      ///   - content: 文本的内容
      ///   - font: 字体
      ///   - width: 宽度
      ///   - height: 高度
      ///   - minimumScaleFactor: 缩放率
      /// - Returns: 文本行数 & 每一行内容
      static func linesCountAndLinesContent(content: String, font: UIFont, width: CGFloat, height: CGFloat, minimumScaleFactor: CGFloat = 1.0) -> (Int?, [String]?) {
          let lodFontName = font.fontName
          let fontSize = getFontSizeForLabel(content: content, minimumScaleFactor: minimumScaleFactor, font: font, width: width, height: height)
          let newFont = UIFont(name: lodFontName, size: fontSize) ?? UIFont.systemFont(ofSize: fontSize)
          let c_fn = newFont.fontName as CFString
          let fp = newFont.pointSize
          let c_f = CTFontCreateWithName(c_fn, fp, nil)
  
          let style = NSMutableParagraphStyle()
          style.lineBreakMode = .byCharWrapping
          let contentDict = [NSAttributedString.Key.paragraphStyle : style] as [NSAttributedString.Key : Any]
          let attr = NSMutableAttributedString(string: content)
          let range = NSRange(location: 0, length: attr.length)
          attr.addAttributes(contentDict, range: range)
          attr.addAttribute(NSAttributedString.Key.font, value: c_f, range: range)
          let frameSetter = CTFramesetterCreateWithAttributedString(attr as CFAttributedString)
    
          let path = CGMutablePath()
          /// 2.5 是经验误差值
          path.addRect(CGRect(x: 0, y: 0, width: width, height: height > (fp * 1.5) ? height : fp * 1.5))
          let framef = CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, 0), path, nil)
          let lines = CTFrameGetLines(framef) as NSArray
          var lineArr = [String]()
          for line in lines {
              let lineRange = CTLineGetStringRange(line as! CTLine)
              let lineString = content.jk.sub(start: lineRange.location, length: lineRange.length)
              lineArr.append(lineString as String)
          }
          return (lineArr.count, lineArr)
      }
  
      // MARK: 获取字体的大小
      /// 获取字体的大小
      /// - Returns: 字体的大小
      private static func getFontSizeForLabel(content: String, minimumScaleFactor: CGFloat, font: UIFont, width: CGFloat, height: CGFloat) -> CGFloat {
          let text: NSMutableAttributedString = NSMutableAttributedString(attributedString: NSAttributedString(string: content))
          text.setAttributes([NSAttributedString.Key.font: font as Any], range: NSMakeRange(0, text.length))
          let context: NSStringDrawingContext = NSStringDrawingContext()
          context.minimumScaleFactor = minimumScaleFactor
          text.boundingRect(with: CGSize(width: width, height: height), options: NSStringDrawingOptions.usesLineFragmentOrigin, context: context)
          let adjustedFontSize: CGFloat = font.pointSize * context.actualScaleFactor
          return adjustedFontSize
      }
  }