[Swift] 限制TextField字數

extension ViewController : UITextFieldDelegate{
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        //最大字數
        let maxLength = 16
        let currentString: NSString = textField.text as! NSString
        let newString: NSString =
            currentString.replacingCharacters(in: range, with: string) as NSString
        //return true時代表可以繼續輸入
        return newString.length <= maxLength
    }
}