How to set delegate of UITextField in separate class in Swift?

Question

I'm trying to implement UITextFieldDelegate in separate class, but it didn't working:

class ViewController: UIViewController {

    @IBOutlet var TextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        let restrictor = TextFieldRestrictController()
        TextField.delegate = restrictor
    }
}

class TextFieldRestrictController : NSObject, UITextFieldDelegate {

    public func textField(_ textField: UITextField,
                          shouldChangeCharactersIn range: NSRange,
                          replacementString string: String) -> Bool {
        let inverseSet = NSCharacterSet(
            charactersIn:"0123456789.").inverted

        let components = string.components(separatedBy: inverseSet)

        let filtered = components.joined(separator:"")
        return string == filtered
    }
}

But this is working:

class ViewController: UIViewController {

    @IBOutlet var TextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        TextField.delegate = self
    }

    public func textField(_ textField: UITextField,
                          shouldChangeCharactersIn range: NSRange,
                          replacementString string: String) -> Bool {
        let inverseSet = NSCharacterSet(
            charactersIn:"0123456789.").inverted

        let components = string.components(separatedBy: inverseSet)

        let filtered = components.joined(separator:"")
        return string == filtered
    }
}

Is there something wrong?

Don't you also need to declare the protocol `UITextFieldDelegate` in the class declaration for your working option for it to be accepted as a delegate ie: `class ViewController: UIViewController, UITextFieldDelegate {` ....? @JasonTW — Chris Lindsey, May 16 '21 at 12:02

score 5 · Accepted Answer · answered May 17 '17 at 09:08

UITextField's .delegate is a weak property so at the end of viewDidLoad method, restrictor will be deallocated because there is no other strong reference around that is pointing to the object which it points to.

You can try printing out ValidationTextField.delegate in viewDidAppear(animated:) and see it returns nil.

To overcome this problem, you can define restrictor as an instance variable so it'll stay alive as long as the view controller is alive:

class ViewController: UIViewController {
  @IBOutlet weak var ValidationTextField: UITextField!

  let restrictor = TextFieldRestrictController()

  override func viewDidLoad() {
    super.viewDidLoad()
    ValidationTextField.delegate = restrictor
  }
}

How to set delegate of UITextField in separate class in Swift?

1 Answers1