private void btnTim_Click(object sender, EventArgs e)
        {
            if ("tim" != act)
            {
                grpThongTin.Enabled = true;
                pnInFor.Visible     = false;
                txtMaNV.Enabled     = true;
                txtMaNV.Clear();
                txtMaNV.Focus();

                act = "tim";
                return;
            }

            dgvNhanVien.DataSource = myNhanVienBUL.TimNhanVienTheoMa(txtMaNV.Text);
        }