I don't know if this is recommended, however since nobody picked up this questions, this is what I do:
I assume you use NSRulerView as an NSScrollView.verticalRulerView property. What I do, is override drawHashMarksAndLabels(in:) and use CoreText to draw numbers in the positions from NSTextLayoutManager
class LineNumberRulerView: NSRulerView {
private weak var textView: NSTextView?
init(textView: NSTextView) {
self.textView = textView
super.init(scrollView: textView.enclosingScrollView!, orientation: .verticalRuler)
clientView = textView.enclosingScrollView!.documentView
NotificationCenter.default.addObserver(forName: NSView.frameDidChangeNotification, object: textView, queue: nil) { [weak self] _ in
self?.needsDisplay = true
}
NotificationCenter.default.addObserver(forName: NSText.didChangeNotification, object: textView, queue: nil) { [weak self] _ in
self?.needsDisplay = true
}
}
public override func drawHashMarksAndLabels(in rect: NSRect) {
guard let context = NSGraphicsContext.current?.cgContext,
let textView = textView,
let textLayoutManager = textView.textLayoutManager
else {
return
}
let relativePoint = self.convert(NSZeroPoint, from: textView)
context.saveGState()
context.textMatrix = CGAffineTransform(scaleX: 1, y: isFlipped ? -1 : 1)
let attributes: [NSAttributedString.Key: Any] = [
.font: textView.font!,
.foregroundColor: NSColor.secondaryLabelColor
]
var lineNum = 1
textLayoutManager.enumerateTextLayoutFragments(from: nil, options: .ensuresLayout) { fragment in
let fragmentFrame = fragment.layoutFragmentFrame
for (subLineIdx, textLineFragment) in fragment.textLineFragments.enumerated() where subLineIdx == 0 {
let locationForFirstCharacter = textLineFragment.locationForCharacter(at: 0)
let ctline = CTLineCreateWithAttributedString(CFAttributedStringCreate(nil, "\(lineNum)" as CFString, attributes as CFDictionary))
context.textPosition = fragmentFrame.origin.applying(.init(translationX: 4, y: locationForFirstCharacter.y + relativePoint.y))
CTLineDraw(ctline, context)
}
lineNum += 1
return true
}
context.restoreGState()
}
}
