无论我做什么，NSLayoutManager 都会隐藏新行字符

我正在尝试显示不可见的字符，例如 NSTextView 子类中的换行符。像重写 NSLayoutManager 的 drawGlyph 方法这样的常用方法是一个坏主意，因为它太慢并且无法在多页布局中正常工作。

我想做的是重写 NSLayoutManager 的 setGlyph 方法，以便它将不可见的“\n”字形替换为“¶”字形，将“ ”替换为“∙”。

它适用于“ ”空格字形，但对新行字符没有影响。

public override func setGlyphs(_ glyphs: UnsafePointer<CGGlyph>, properties props: UnsafePointer<NSGlyphProperty>, characterIndexes charIndexes: UnsafePointer<Int>, font aFont: Font, forGlyphRange glyphRange: NSRange) {
    var substring = (self.currentTextStorage.string as NSString).substring(with: glyphRange)

    // replace invisible characters with visible
    if PreferencesManager.shared.shouldShowInvisibles == true {
        substring = substring.replacingOccurrences(of: " ", with: "\u{00B7}")
        substring = substring.replacingOccurrences(of: "\n", with: "u{00B6}")
    }

    // create a CFString
    let stringRef = substring as CFString
    let count = CFStringGetLength(stringRef)

    // convert processed string to the C-pointer
    let cfRange = CFRangeMake(0, count)
    let fontRef = CTFontCreateWithName(aFont.fontName as CFString?, aFont.pointSize, nil)
    let characters = UnsafeMutablePointer<UniChar>.allocate(capacity: MemoryLayout<UniChar>.size * count)
    CFStringGetCharacters(stringRef, cfRange, characters)

    // get glyphs for the pointer of characters
    let glyphsRef = UnsafeMutablePointer<CGGlyph>.allocate(capacity: MemoryLayout<CGGlyph>.size * count)
    CTFontGetGlyphsForCharacters(fontRef, characters, glyphsRef, count)

    // set those glyphs
    super.setGlyphs(glyphsRef, properties:props, characterIndexes: charIndexes, font: aFont, forGlyphRange: glyphRange)
}

然后我想到了一个想法：看起来 NSTypesetter 标记了新行字符范围，就像那些根本不应该处理的字符范围一样。所以我继承了 NSTypesetter 并重写了一个方法：

override func setNotShownAttribute(_ flag: Bool, forGlyphRange glyphRange: NSRange) {
    let theFlag = PreferencesManager.shared.shouldShowInvisibles == true ? false : true
    super.setNotShownAttribute(theFlag, forGlyphRange: glyphRange)
}

但这不起作用。无论我创建什么字形，NSLayoutManager 仍然不会为新行字符生成字形。

我究竟做错了什么？

对于这个问题来说，这可能已经不再有用了，但我是通过谷歌到达这里的。

至少在 macOS 10.14 上进行测试时，-[NSLayoutManager setNotShownAttribute:forGlyphAtIndex:]能够在生成该索引的字形后更改其值。关键是会无条件setNotShownAttribute:YES用于布置行末尾的换行字形。你得到-[NSLayoutManagerDelegate layoutManager:shouldUseAction:forControlCharacterAtIndex:]完成后，您可以在那里重置它：

- (NSControlCharacterAction)layoutManager:(NSLayoutManager *)layoutManager shouldUseAction:(NSControlCharacterAction)action forControlCharacterAtIndex:(NSUInteger)characterIndex {
  if (layoutManager.showsInvisibleCharacters && (action & NSControlCharacterActionLineBreak)) {
    [layoutManager setNotShownAttribute:NO forGlyphAtIndex:[layoutManager glyphIndexForCharacterAtIndex:characterIndex]];
  }

  return action;
}

func layoutManager(_ layoutManager: NSLayoutManager, shouldUse action: NSLayoutManager.ControlCharacterAction, forControlCharacterAt characterIndex: Int) -> NSLayoutManager.ControlCharacterAction {
  if layoutManager.showsInvisibleCharacters, action.contains(.lineBreak) {
    let glyphIndex = layoutManager.glyphIndexForCharacter(at: characterIndex)
    layoutManager.setNotShownAttribute(false, forGlyphAt: glyphIndex)
  }

  return action
}

你会注意到我使用showsInvisibleCharacters在示例中，它实际上适用于内置方法，即使它没有该字符的映射，从而产生“我不知道”字形：

With -[NSLayoutManagerDelegate layoutManager:shouldGenerateGlyphs:properties:characterIndexes:font:forGlyphRange:，你可以让它完美工作：