private void CommandBinding_CanExecute_Xoa(object sender, CanExecuteRoutedEventArgs e)
        {
            if (dg == null)
            {
                return;
            }
            CChuyenKhoaModel a = (CChuyenKhoaModel)dg.SelectedItem;

            if (dg.SelectedItem != null
                )
            {
                e.CanExecute = true;
            }
        }
        private void CommandBinding_CanExecute_Sua(object sender, CanExecuteRoutedEventArgs e)
        {
            if (dg == null)
            {
                return;
            }
            CChuyenKhoaModel a = (CChuyenKhoaModel)dg.SelectedItem;

            if (a != null &&
                a.MaChuyenKhoa == txtMaChuyenKhoa.Text)
            {
                e.CanExecute = true;
            }
        }