private void btnThem_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
 {
     nbcDSDocGia.OptionsNavPane.NavPaneState = DevExpress.XtraNavBar.NavPaneState.Expanded;
     if (them)
     {
         tbTenDG.Clear();
         tbDiaChi.Clear();
         tbSDT.Clear();
         tbDonVi.Clear();
         string maDG = nextMa(DocGia_BUS.LastMaDG());
         //
         them = false;
         DGbindingSource.AddNew();
         //mã sinh viên tự tăng
         gvDocGia.SetFocusedRowCellValue(colMaDG, maDG);
         tbMaDG.Text = maDG.ToString();
         //trỏ tới dòng cuối cùng trong gridview
         gvDocGia.FocusedRowHandle = gvDocGia.RowCount - 1;
         tbTenDG.Focus();
     }
     else
     {
         gvDocGia.FocusedRowHandle = gvDocGia.RowCount - 1;
         tbTenDG.Focus();
     }
     // frm.Show();
 }