private void DeleteButton_Click(object sender, RoutedEventArgs e)
        {
            GroupNumber grpno = (GroupNumber)dataGridgrpNo.SelectedItem;

            GroupNumberDataService groupNumberData = new GroupNumberDataService(new EntityFramework.TimetableManagerDbContext());

            groupNumberData.DeleteGroupNumbers(grpno.Id).ContinueWith(result =>
            {
                MessageBox.Show("Deleted");
            });

            _ = GroupNumberDataList.Remove(grpno);
        }
        public async Task load()
        {
            GroupNumberDataService groupNumberDataService = new GroupNumberDataService(new EntityFramework.TimetableManagerDbContext());

            GroupNumberList = await groupNumberDataService.GetGroupNumbers();

            GroupNumberList.ForEach(e =>
            {
                GroupNumber l = new GroupNumber();
                l.Id          = e.Id;
                l.GroupNum    = e.GroupNum;
                GroupNumberDataList.Add(l);
            });
        }