public TransactionViewModel()
 {
     mainAtt     = MainAtt.getInstance();
     voucherVm   = new VoucherViewModel();
     dtServiceVM = new DetailServiceViewModel();
     stockVM     = new StockViewModel();
     initDB();
 }
 public TransactionViewModel(string htID)
 {
     mainAtt     = MainAtt.getInstance();
     Ht          = mainAtt.Mydb.HeaderTransactions.Where(a => a.HeaderID.Equals(htID)).FirstOrDefault();
     voucherVm   = new VoucherViewModel();
     dtServiceVM = new DetailServiceViewModel();
     stockVM     = new StockViewModel();
     initDB();
     UpdateTotalPrice();
 }