private void DangNhap() { lblError.Visible = false; string userName = txtUserName.Text.Trim(); string password = txtPassword.Text; NguoiDung nguoiDung = _nguoiDungDAL.DangNhap(userName, password); if (nguoiDung != null) { CurrentUser = nguoiDung; this.DialogResult = DialogResult.OK; } else { lblError.Visible = true; } }