private void button3_Click(object sender, EventArgs e) { List <int> hs = new List <int>(); HSB.Loadhsl(classcombo.SelectedItem.ToString()); if (HocSinhDTO.lisths.Count > 0) { foreach (var x in HocSinhDTO.lisths) { HSB.GetMaHS(x.Email); HSB.DelBD(HocSinhDTO.id); } } foreach (var s in clasDTO.lop) { if (s.TenL1 == classcombo.SelectedItem.ToString()) { HSB.DelClass(s.MaL1); HSB.Load(); HSB.loadBCM(); HSB.Loadkl(); MessageBox.Show("successful"); break; } } }