Computer Programming Concepts and Visual Basic David I. Schneider

clicked or a Move, Update, Delete, or AddNew method is executed. The general form of the
Validate event procedure is
Private Sub Data1_Validate(Action As Integer, Save As Integer)
statement(s)
End Sub
The value of Action identifies the specific operation that triggered the event and the value of
Save specifies whether data bound to the control has changed. You can change the value of the
Action argument to perform a different action. Some values of the Action argument are shown
in Table 11.3.
TABLE 11.3
Some Values of the Action Argument
Value Description
1 MoveFirst method
2 MovePrevious method
3 MoveNext method
4 MoveLast method
5 AddNew method
6 Update operation (not UpdateRecord)
7 Delete method
10 Close method
If you assign 0 to the Action argument, the operation will be canceled when the Validate
event procedure is exited.
The value of Save is –1 (True) if the data in any control attached to the data control have
changed and is 0 (False) otherwise. If you set the value of Save to 0 in the Validate event procedure,
any changes will not be saved.
Consider the form created in the walkthrough. Suppose the contents of txtPop1995, the
1995 population text box, is changed to .8 and then a navigator arrow is clicked in an attempt
to move to another record. The following code prevents the move.
Private Sub datCities_Validate(Action As Integer, Save As Integer)
Dim strMsg As String
If val(txtPop1995) < 1 then
strMsg = “We only allow cities having a population ” & _ “at least one
million.”
MsgBox strMsg“City too small!”
Action = 0
End If
End Sub
If the statement
Action = 0
is changed to
Save = 0
the move will take place, but the previous record will retain its original values. That is, the number
.8 will not appear in the table.
EXAMPLE 1
An Introduction to Databases 327
The following program is a general database manager for the Cities table in the MEGACTY1.MDB database.
It allows the user to edit the Cities table as needed and to locate information based on the city name.
(In the Validate event procedure, the inner If block keeps the message box from appearing when the first
or last record is deleted.)