private void cbbChuongTrinhHoc_SelectedIndexChanged(object sender, EventArgs e) { try { if (cbbChuongTrinhHoc.DataSource == null) { MessageBox.Show("Chuong trinh hoc hien tai chua co lop.", "Lỗi", MessageBoxButtons.OK, MessageBoxIcon.Information); cbbLopHoc.DataSource = null; } else { _dtlop = _objlopbus.GetMaTen_TheoChuongTrinhHoc(cbbChuongTrinhHoc.SelectedValue.ToString()); if (_dtlop.Rows.Count != 0) { cbbLopHoc.DataSource = _dtlop; cbbLopHoc.ValueMember = "MaLop"; cbbLopHoc.DisplayMember = "TenLop"; lblHocPhi.Text = String.Format("{0:0,0}", _objchuongtrinhhocbus.GetHocPhi_TheoMaChuongTrinhHoc(cbbChuongTrinhHoc.SelectedValue.ToString())); } else { cbbChuongTrinhHoc.DataSource = null; } } } catch { } }