Visual Basic.NET How to Program (PDF)

826 Files and Streams Chapter 17
41 ' invoked when user clicks Delete Record button
42 Protected Sub cmdDelete_Click(ByVal sender As System.Object, _
43 ByVal e As System.EventArgs) Handles cmdDelete.Click
44
45 Dim record As CRandomAccessRecord = _
46 transactionProxy.GetRecord(txtAccount.Text)
47
48 ' if record exists, delete it in file
49 If (record Is Nothing) = False Then
50 DeleteRecord(record)
51 End If
52
53 Me.Hide()
54 showPreviousWindow()
55 End Sub ' cmdDelete_Click
56
57 ' invoked when user clicks Cancel button
58 Protected Sub cmdCancel_Click(ByVal sender As System.Object, _
59 ByVal e As System.EventArgs) Handles cmdCancel.Click
60
61 Me.Hide()
62 showPreviousWindow()
63 End Sub ' cmdCancel_Click
64
65 ' delete record in file at position specified by accountNumber
66 Public Sub DeleteRecord(ByVal record As CRandomAccessRecord)
67
68 Dim accountNumber As Integer = record.Account
69
70 ' display error message if record does not exist
71 If record.Account = 0 Then
72 MessageBox.Show("Record Does Not Exist", "Error", _
73 MessageBoxButtons.OK, MessageBoxIcon.Error)
74 txtAccount.Clear()
75
76 Return
77 End If
78
79 ' create blank record
80 record = New CRandomAccessRecord()
81
82 ' write over file record with empty record
83 If (transactionProxy.AddRecord( _
84 record, accountNumber) = True) Then
85
86 ' notify user of successful deletion
87 MessageBox.Show("Record Deleted", "Success", _
88 MessageBoxButtons.OK, MessageBoxIcon.Information)
89 Else
90
91 ' notify user of failure
92 MessageBox.Show("Record could not be deleted", "Error", _
Fig. 17.23 FrmDeleteDialog class enables users to remove records from files in
transaction-processor case study (part 2 of 3).