CLC_empty_ field.swift

class CreateListController: UITableViewController {
    @IBOutlet weak var doneBarButton: UIBarButtonItem!
    @IBOutlet weak var nameTextField: UITextField!
    // ..
    // ..
    var chooseIconTapped = false
  
    override func viewDidLoad() {
      super.viewDidLoad()
      handleEmptyFields()
    }
  
    override func viewWillAppear(_ animated: Bool) {
      super.viewWillAppear(animated)
      checkFields()
    }
  
    func handleEmptyFields() {
      doneBarButton.isEnabled = false
      nameTextField.delegate = self
    }

    func checkFields() {
      if list != nil || chooseIconTapped && nameTextField.text!.count > 0 {
        doneBarButton.isEnabled = true
      }
    }
}

extension CreateListController: UITextFieldDelegate {
  func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let text = (nameTextField.text! as NSString).replacingCharacters(in: range, with: string)
    if text.isEmpty || !chooseIconTapped {
      doneBarButton.isEnabled = false
    } else {
      doneBarButton.isEnabled = true
    }
    return true
  }
}