How to live check a NSTextField - Swift OS X

I am currently making an OS X application written in Swift. What I want to do is when the user enters text in a NSTextField, I want to run a function that checks the value and adds it to a Label. How would I do this in swift?

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
         }
      }
   }
}