Visual Basic.NET How to Program (PDF)

824 Files and Streams Chapter 17
Fig. 17.22 FrmUpdateDialog class enables users to update records in transactionprocessor
case study (part 6 of 6).
The Transaction TextBox initially contains the string Charge or Payment. The
user should select this text, type the transaction amount (a positive value for a charge or a
negative value for a payment) and then press Enter. The program calls method
txtTransactionNumber_KeyDown (lines 85–129) to add the user-specified transaction
amount to the current balance.
The user clicks the Save Changes button to write the altered contents of the Text-
Boxes to the file. (Note that pressing Save Changes does not update the Balance
field—the user must press Enter to update this field before pressing Save Changes.)
When the user clicks Save Changes, the program invokes method cmdSave_Click
(lines 132–147), which calls Private method UpdateRecord (lines 159–190). This
method calls method AddRecord of the CTransaction object (lines 174–175) to store
the TextBox values in a CRandomAccessRecord and overwrite the existing file
record with the CRandomAccessRecord containing the new data.
When the user clicks the Delete Record button of the Start Dialog, the program
invokes method cmdDelete_Click of class FrmStartDialog (Fig. 17.20, lines