private void _statsByItemBackground_DoWork(object sender, DoWorkEventArgs e)
 {
     if (_bills != null)
     {
         foreach (Bill b in _bills)
         {
             foreach (Item i in b.Items)
             {
                 using (StatsByItems statItem = _statsByItemsList.FirstOrDefault(x => x.Item.Id == i.Id))
                 {
                     if (statItem != null)
                     {
                         statItem.Quantity++;
                         statItem.Total += (int)(i.SalingPrice * (100 - b.DiscountRate));
                     }
                     else
                     {
                         _statsByItemsList.Add(new StatsByItems {
                             Item = i, Quantity = 1, Total = i.SalingPrice
                         });
                     }
                 }
             }
         }
     }
 }
        private void _backgroundShowStats_DoWork(object sender, DoWorkEventArgs e)
        {
            DateTime fromDate = _dpickerFrom.Value;
            DateTime toDate   = _dpickerTo.Value;

            List <Bill> bills = _billBo.GetBills(fromDate, toDate);

            if (bills != null)
            {
                foreach (Bill b in bills)
                {
                    foreach (Item i in b.Items)
                    {
                        using (StatsByItems statItem = _statsItemList.FirstOrDefault(x => x.Item.Id == i.Id))
                        {
                            if (statItem != null)
                            {
                                statItem.Quantity++;
                                statItem.Total += (int)(i.SalingPrice * (100 - b.DiscountRate) / 100.0);
                            }
                            else
                            {
                                _statsItemList.Add(new StatsByItems {
                                    Item = i, Quantity = 1, Total = i.SalingPrice
                                });
                            }
                        }
                    }
                }
            }
        }