Using Custom button to add variable item code

I need to use custom button to add item code to transaction screen but my Item code not always same Item, it can change Itemlookupcode depend on condition including Price or Quantity so that I cannot use Internal command 'PerformAddItem' , I write dll to use qsrules but it's not working , my code like these: Public Function Process(session as Qsrules.Sessionclass) as Boolean dim Entry as TransactionEntry Entry Session.Transaction.Entries.Add(1,"11200",1,False,1,,,False) Entry.SetPrice(300) end function