private void btnFilter_Click(object sender, EventArgs e)
        {
            try
            {
                cboNhaSx.Text  = "";
                cboLoaiSp.Text = "";

                int i = 0;
                tk.DateOne = DateTime.Parse(dtmTuNgay.Value.ToShortDateString());
                tk.DateTwo = DateTime.Parse(dtmDenNgay.Value.ToShortDateString());

                List <ThongKe> tklist = tkbll.ThongKeDonDatHangTheoNgayThang(tk);
                dgvThongKeDonHang.Rows.Clear();
                foreach (ThongKe tks in tklist)
                {
                    DataGridViewRow row = new DataGridViewRow();
                    row.CreateCells(dgvThongKeDonHang);
                    row.Cells[0].Value = i + 1;
                    row.Cells[1].Value = tks.MaSp;
                    row.Cells[2].Value = tks.TenSp;
                    row.Cells[3].Value = tks.TenLoai;
                    row.Cells[4].Value = tks.TenSx;
                    row.Cells[5].Value = tks.Sld;

                    dgvThongKeDonHang.Rows.Add(row);
                    ++i;
                }
                cboTongDondh.Text      = i.ToString();
                cboTongSldh.DataSource = tkbll.TongSldhTheoNgayDh(tk);
            }
            catch (Exception ex)
            {
                MessageBox.Show("Lỗi Filter!" + ex.Message);
            }
        }