private void btxoa_Click(object sender, EventArgs e) { GiaoVienDAL gvDAL = new GiaoVienDAL(); if (tbMagv.TextLength == 0) { MessageBox.Show("Chua co ma giao vien", " loi "); } else { try { int id = Convert.ToInt16(tbMagv.Text); gvDAL.deleteGiaoVien(id); dgvGiaoVien.DataSource = gvDAL.LoadDS(); } catch { MessageBox.Show("ma Giao Vien khong thoa man", " loi "); } } }