private void RefreshDTGV()
{
dtgvThongKe.Rows.Clear();
int ID = dtgvThongKe.Rows.Count + 1;
ThongKe NV = new ThongKe();
foreach (THONGKEDONHANGDABAN item in NV.ThongKeSanPham())
{
dtgvThongKe.Rows.Add(ID, item.MADH, item.TENKH, item.TENNV, item.TIMEXUAT, item.THANHTIEN);
ID++;
}
lbTongTien.Text = String.Format("{0:n0} VNĐ", NV.TongThanhTien());
}