Blackjacx

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
  
    let strippedString = <change replacements string so it fits your requirement - strip, trim, etc>

    // replace current content with stripped content
    if let replaceStart = textField.position(from: textField.beginningOfDocument, offset: range.location),
        let replaceEnd = textField.position(from: replaceStart, offset: range.length),
        let textRange = textField.textRange(from: replaceStart, to: replaceEnd) {

        textField.replace(textRange, withText: strippedString)