private void btnLapHoaDonMoi_Click(object sender, EventArgs e)
 {
     i                       = 0;
     Tien                    = 0;
     txtTongtien.Text        = "0";
     btnLapHoaDonMoi.Enabled = false;
     btnThemSP.Enabled       = false;
     pbcheck.Enabled         = true;
     btnIn.Enabled           = true;
     txtMaKH.ReadOnly        = false;
     txtSoHD.Text            = HoaDonBanHangBUS.GetIDHoaDon();
     txtMaSP.ResetText();
     txtTenSP.ResetText();
     txtGiamGia.ResetText();
     txtGiaBan.ResetText();
     txtMaKH.ResetText();
     dtkNgayLap.Value = DateTime.Now;
     dgvDanhSach.Rows.Clear();
 }