private void BtnThongKe_Click(object sender, EventArgs e)
        {
            try
            {
                string cbbSelected = cbbSelectThongKe.SelectedItem.ToString();
                if (cbbSelected == "Ngày" || cbbSelected == "Tháng" || cbbSelected == "Năm" || cbbSelected == "Tổng")
                {
                    dtgvThongKe.Rows.Clear();
                    int     ID           = dtgvThongKe.Rows.Count + 1;
                    ThongKe NV           = new ThongKe();
                    string  valueThongke = cbbSelectThongKe.SelectedItem.ToString();
                    foreach (THONGKEDONHANGDABAN item in NV.THONGKETHEONTN(dTimePicker.Value, valueThongke))
                    {
                        dtgvThongKe.Rows.Add(ID, item.MADH, item.TENKH, item.TENNV, item.TIMEXUAT, item.THANHTIEN);
                        ID++;
                    }

                    lbTongTien.Text = String.Format("{0:n0} VNĐ", NV.TongThanhTien());
                }

                if (cbbSelected == "Quý")
                {
                    dtgvThongKe.Rows.Clear();
                    int     ID           = dtgvThongKe.Rows.Count + 1;
                    ThongKe NV           = new ThongKe();
                    string  valueThongke = cbbQuy.SelectedItem.ToString();
                    foreach (THONGKEDONHANGDABAN item in NV.TKQuy(dTimePicker.Value, valueThongke))
                    {
                        dtgvThongKe.Rows.Add(ID, item.MADH, item.TENKH, item.TENNV, item.TIMEXUAT, item.THANHTIEN);
                        ID++;
                    }

                    lbTongTien.Text = String.Format("{0:n0} VNĐ", NV.TongThanhTien());
                }
            }
            catch (Exception)
            {
            }
        }