title: How to identify which UITextField was changed with textFieldDidChange
body: <p>I am using several <code>UITextField</code>s and want to do anytime anything changes in any one of them.</p>
  
  <p>It looks basically like:</p>
  
  <pre><code>@IBOutlet weak var f1: UITextField!
  @IBOutlet weak var f2: UITextField!
  @IBOutlet weak var f3: UITextField!
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      f1.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
      f2.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
      f3.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
  }
  
  @objc func textFieldDidChange(_ textField: UITextField) {
      // Data in one of the fields changed.
      if self.view.tag == 1 {
          print("field 1")
      } else {
          if self.view.tag == 2 {
              print("field 2")
          }
          //...
      }
  }
  </code></pre>
  
  <p>As you can see, I've tried setting tags, but not sure how to access them here.</p>
  
  <p>I’m using XCode 9.01 and Swift 4.</p>