}//end method RunServer // When click on login button private void btn_Login_Click(object sender, EventArgs e) { //Save in variables text values on fields string username = txt_Username.Text; string password = txt_Password.Text; //regex for validation text fields string regFormat = @"^[a-zA-Z0-9.]{5,20}$"; Regex reg = new Regex(regFormat); Match matchUsername = reg.Match(username); Match matchPassword = reg.Match(password); //Is validate successfully username if (!matchUsername.Success) { lbl_ErrorMSGUsername.Text = "Your username is too short!"; lbl_ErrorMSGPassword.Text = ""; } //Is validate successfully password else if (!matchPassword.Success) { lbl_ErrorMSGPassword.Text = "Your password is too short!"; lbl_ErrorMSGUsername.Text = ""; } else { // clear error messages lbl_ErrorMSGPassword.Text = ""; lbl_ErrorMSGUsername.Text = ""; Users users = (Users)Easy.load("users.xml"); if (users.Username == username && users.Password == password) { var win = new BankCards(); win.Show(); } else { Users user = new Users(username, password); String filename = "users.xml"; Easy.save(user, filename); var win = new BankCards(); win.Show(); } } } // end method btn_Login_Click