如何使用UitextView和NslayoutManager调整自定义下划线的垂直位置，并使用非零线条nsparagragraphStyle？

Question

我想自定义nsSattributtedString的下划线样式，因为statersDot实际上只是短dashes，我实际上想要圆形的点（例如，请参见 nsattributtedstring（ios7+）中的自定义下划线模式）。

我已经走了很远，但是我的下划线遇到了不一致的一致性问题，这显然是由于定制线间距。如果下划线不在最后一行的文本中，那么下划线就太远了，但是如果它在最后一行的文本上，则太远了。大概是因为最后一行没有任何线间距。我想如果有办法，在我的drawunderline内，我可以相应地调整y偏移量，但是有一种简单的方法吗？

示例：

class DotUnderlineLayoutManager: NSLayoutManager {
  let color: UIColor

  init(color: UIColor = .black) {
    self.swatch = swatch
    super.init()
  }

  override func drawUnderline(forGlyphRange glyphRange: NSRange, underlineType _: NSUnderlineStyle, baselineOffset: CGFloat, lineFragmentRect: CGRect, lineFragmentGlyphRange _: NSRange, containerOrigin: CGPoint) {
    guard let container = textContainer(
      forGlyphAt: glyphRange.location,
      effectiveRange: nil
    ) else { return }

    let rect = boundingRect(forGlyphRange: glyphRange, in: container)

    let offsetRect = rect.offsetBy(
      dx: containerOrigin.x,
      dy: containerOrigin.y // + baselineOffset <- adding this helps a bit with an underline on the last line but messes up other lines even more
    )

    let path = UIBezierPath()
    path.strokeDottedLine(under: offsetRect, color: color)    
  }
}

private extension UIBezierPath {
  func strokeDottedLine(under rect: CGRect, color: UIColor) {
    lineWidth = 2
    lineCapStyle = .round
    setLineDash([0.1, 5], count: 2, phase: 0)
    move(to: .init(x: rect.minX, y: rect.maxY))
    addLine(to: .init(x: rect.maxX, y: rect.maxY))
    color.setStroke()
    stroke()
  }
}



extension NSUnderlineStyle {
  static var patternCircularDot: NSUnderlineStyle {
    NSUnderlineStyle(rawValue: 0x11)
  }
}

let textView: UITextView = {
    let layout = DotUnderlineLayoutManager(swatch: swatch)
    let storage = NSTextStorage()
    storage.addLayoutManager(layout)
    let initialSize = CGSize(width: 0, height: CGFloat.greatestFiniteMagnitude)
    let container = NSTextContainer(size: initialSize)
    container.widthTracksTextView = true
    layout.addTextContainer(container)

    let textView = UITextView(frame: .zero, textContainer: container)
    textView.isUserInteractionEnabled = false
    textView.isEditable = false
    textView.isScrollEnabled = false
    textView.backgroundColor = .clear
    return textView
}()

let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineBreakMode = .byWordWrapping
paragraphStyle.lineSpacing = 10 // any non-zero value

textView.attributedText = NSAttributedString(
    string: myText,
    attributes: [
        .paragraphStyle: paragraphStyle
        .underlineStyle: NSUnderlineStyle.patternCircularDot.union(.single).rawValue
    ]
)

编辑：自定义字体实际上并不重要，仅在段落样式上的线间距就相应地简化了问题：

Answer 1

通过nsmutableParagragraphStyle设置行间距。

func layoutManager(_ layoutManager: NSLayoutManager, lineSpacingAfterGlyphAt glyphIndex: Int, withProposedLineFragmentRect rect: CGRect) -> CGFloat {
    // set line spacing as needed here
}

而不是通过nsmutableParagragraphStyle使用nslay> nslayoutmanagerdelegate's layoutmanager（linespacingafterterglyphat…）我什至设置了我的nslayoutmanager作为自己的委托子类。疯了，我知道。

然后，我调整了矩形以减去一半间距，这似乎很好。