UITextField, automatically move to next after 1 character

Question

Scenario: I have 4 UITextFields that only accept 1 character. Easy.

Problem: After I enter the 1 character, I want the next TextField to become active automatically with

Answer 1

Swift 4.x

textField.addTarget(self, action: #selector(self.textFieldDidChange(textField:)), for: .editingChanged)

---

@objc func textFieldDidChange(textField: UITextField)
{
    let text = textField.text
    if text?.utf16.count == 1 {
        switch textField {
        case txtOtpNumber1:
            txtOtpNumber2.becomeFirstResponder()
        case txtOtpNumber2:
            txtOtpNumber3.becomeFirstResponder()
        case txtOtpNumber3:
            txtOtpNumber4.becomeFirstResponder()
        case txtOtpNumber4:
            txtOtpNumber4.resignFirstResponder()
        default:
            break
        }
    } else {
        switch textField {
        case txtOtpNumber4:
            txtOtpNumber3.becomeFirstResponder()
        case txtOtpNumber3:
            txtOtpNumber2.becomeFirstResponder()
        case txtOtpNumber2:
            txtOtpNumber1.becomeFirstResponder()
        case txtOtpNumber1:
            txtOtpNumber1.resignFirstResponder()
        default:
            break
        }
    }
}

_{PS. Chetan's answer updated for the current Swift.}