private void TxtUserEmail_TextChanged(object sender, EventArgs e)
        {
            AppUser appUser = new AppUser()
            {
                UserName     = txtUserName.Text,
                UserPassword = txtUserPassword.Text,
                UserEmail    = txtUserEmail.Text
            };

            bool checkSignUp = signUpController.UserSignUpEmailControll(appUser);

            if (checkSignUp)
            {
                lblEmailCheck.Text      = "Valid Email Format";
                lblEmailCheck.ForeColor = Color.Green;
            }
            else
            {
                lblEmailCheck.Text      = "Invalid Email Format!";
                lblEmailCheck.ForeColor = Color.Red;

                //MessageBox.Show("Error!");
            }
        }