// Làm nhiệm vụ validate account, trả về một dictionary các lỗi.
        public Dictionary <string, string> CheckValidate()
        {
            YYAccountModel model = new YYAccountModel();
            Dictionary <string, string> errors = new Dictionary <string, string>();

            if (string.IsNullOrEmpty(this._username))
            {
                errors.Add("username", "Username can not be null or empty.");
            }
            else if (this._username.Length < 6)
            {
                errors.Add("username", "Username is too short. At least 6 characters.");
            }
            else if (model.CheckExistUsername(this._username))
            {
                // Check trùng username.
                errors.Add("username", "Username is exist. Please try another one.");
            }
            if (_cpassword != _password)
            {
                errors.Add("password", "Confirm password does not match.");
            }

            // if else if else ...
            return(errors);
        }