How to live check a NSTextField - Swift OS X

1. Conforms ViewController to protocol NSTextDelegate.
2. Assign ViewController as Delegate for TextField.

3. Implement controlTextDidChange method.

   import Cocoa
   
   @NSApplicationMain
   class AppDelegate: NSObject, NSApplicationDelegate, NSTextFieldDelegate {
   
       @IBOutlet weak var window: NSWindow!
       @IBOutlet weak var textField: NSTextField!
       @IBOutlet weak var label: NSTextField!
   
   
       func applicationDidFinishLaunching(aNotification: NSNotification)
       {
           textField.delegate = self
       }
   
       override func controlTextDidChange(notification: NSNotification)
       {
           let object = notification.object as! NSTextField
           self.label.stringValue = object.stringValue
       }
   
       func applicationWillTerminate(aNotification: NSNotification) {
           // Insert code here to tear down your application
       }
   }
   

in ViewController:

import Cocoa

class ViewController: NSViewController, NSTextDelegate {

   @IBOutlet weak var label: NSTextField!
   @IBOutlet weak var label2: NSTextField!
   @IBOutlet weak var textField: NSTextField!
   @IBOutlet weak var textField2: NSTextField!

   override func viewDidLoad() {
      super.viewDidLoad()
   }

   override func controlTextDidChange(notification: NSNotification) {
      if let txtFld = notification.object as? NSTextField {
         switch txtFld.tag {
         case 201:
            self.label.stringValue = txtFld.stringValue
         case 202:
            self.label2.stringValue = txtFld.stringValue
         default:
            break
         }
      }
   }
}

swift 5 xcode 10

//TODO: move oin a better place?
extension NSTextField{ func controlTextDidChange(obj: NSNotification){} }


    class TracksController:NSViewController,
        NSTextFieldDelegate
    {
...
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        //Search bar:
        self.searchBar.delegate = self

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(controlTextDidChange(_:)),
                                               name: NSTextView.didChangeSelectionNotification,
                                               object: nil)

    }

//MARK: NSTextFieldDelegate

func controlTextDidChange(_ obj: Notification)
{
    guard let object = obj.object as? NSTextView else{
        return
    }


    let delegate = object.delegate
    guard  let searchField = delegate as? NSSearchField else {
        return
    }

    let text = searchField.stringValue
    print(text)

}

I know it’s been answered some while ago but I did eventually find this solution for macOS in Swift 3 (it doesn’t work for Swift 4 unfortunately) which notifies when a textfield is clicked inside and for each key stroke.

Add this delegate to your class:-

NSTextFieldDelegate

In viewDidLoad()

NotificationCenter.default.addObserver(self, selector: #selector(textDidChange(_:)), name: Notification.Name.NSTextViewDidChangeSelection, object: nil)

Then add this function:-

    func textDidChange(_ notification: Notification) {
        print("Its come here textDidChange")
        guard (notification.object as? NSTextView) != nil else { return }
        let numberOfCharatersInTextfield: Int = textFieldCell.accessibilityNumberOfCharacters()
        print("numberOfCharatersInTextfield = \(numberOfCharatersInTextfield)")
}

Hope this helps others.