How to do a live UITextField count while typing (Swift)?

Question

I would like to count the character when user keep typing in UITextField with swift.

Image of Field and Label:

Answer 1

Here's how you could do it in Swift 3/4.

First, make sure you've got your textField's delegate set in viewDidLoad.

yourTextField.delegate = self

Then, implement shouldChangeCharactersIn:

extension YourViewController: UITextFieldDelegate {
    func textField(_ textFieldToChange: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
      // limit to 4 characters
      let characterCountLimit = 4

      // We need to figure out how many characters would be in the string after the change happens
      let startingLength = textFieldToChange.text?.characters.count ?? 0
      let lengthToAdd = string.characters.count
      let lengthToReplace = range.length

      let newLength = startingLength + lengthToAdd - lengthToReplace

      return newLength <= characterCountLimit
    } 
}

Additional details here