Multi-line NSTextField not working

I have been trying to get a multi-line NSTextField to lay out automatically using preferredMaxLayoutWidth. I can’t figure out why this doesn’t work.

class ViewController: NSViewController {
   override func viewDidLoad() {
      super.viewDidLoad()

      let textField = NSTextField()
      textField.cell!.usesSingleLineMode = false
      textField.cell!.wraps = true
      textField.cell!.lineBreakMode = .byCharWrapping
      view.addSubview(textField)

      textField.translatesAutoresizingMaskIntoConstraints = false
      NSLayoutConstraint.activate([
         textField.topAnchor.constraintEqual(to: view.topAnchor),
         textField.leadingAnchor.constraintEqual(to: view.leadingAnchor),
         textField.widthAnchor.constraintEqual(toConstant: 20)
      ])
      textField.preferredMaxLayoutWidth = 20
      textField.stringValue = "abcdefghijklmnopqrstuvwxyz"

      view.needsLayout = true
      view.layoutSubtreeIfNeeded()
      print("Intrinsic content size: \(textField.intrinsicContentSize)")
      print("Fitting size: \(textField.fittingSize)")
   }
}

This prints:

Intrinsic content size: (-1.0, 21.0)

Fitting size: (20.0, 21.0)

(21.0 is the size for a single line.)

OK. So it turns out that when an NSTextField is in edit mode, a secret NSTextView (aka the “field editor”) takes over for the editing portion. Text changes are not synced back to the text field until editing has ended. This explains why my sample code only works in non-edit mode.

You can force the sync to occur by accessing the NSTextField.stringValue property. This is what I’ve done in a NSTextField subclass. I also provided my own implementation of intrinsicContentSize because Apple’s implementation doesn’t work in edit mode and is buggy in non-edit mode.