Max Character Limit for TextField - ios

Question

I am looking to cap the amount of characters a user can type into a textfield at 14. Here is the code that I have found documentation on.
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
let currentCharacterCount = userNameTextField.text?.characters.count ?? 0
if (range.length + range.location > currentCharacterCount){
return false
}
let newLength = currentCharacterCount + string.characters.count - range.length
return newLength <= 14
}
but I do not feel that I am implementing this correctly. I have set
userNameTextField.delegate = self
in the viewDidLoad, and I am conforming to the UITextFieldDelegate protocol.

Answer 1

You state you are using Swift 3. The signature of many methods changed in Swift 3. You need to use:
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
}
Not the old signature posted in your question.
If it's still not being called, then you never set the text field's delegate property.

Answer 2

Try this instead:
func textField(textField: UITextField!, shouldChangeCharactersInRange range: NSRange, replacementString string: String!) -> Bool {
let currentString: NSString = (textField.text ?? "") as NSString
let newString = currentString.replacingCharacters(in: range, with: string)
return newString.characters.count <= 14
}

Answer 3

Try this for swift 3:
let limit=4;
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
guard let text = txtSMSCode.text else { return true }
let newLength = text.characters.count + string.characters.count - range.length
return newLength <= limit
}