Private Sub object_BeforeUpdate(Cancel As Integer)
Object The name of a form or a control.
Cancel The setting determines if the BeforeUpdate event occurs. Setting the Cancel argument to True (–1) cancels the BeforeUpdate event.
Remarks
Changing data in a control by using Visual Basic or a macro containing the SetValue action doesn't trigger these events for the control. However, if you then move to another record or save the record, the form's BeforeUpdate event does occur.
The BeforeUpdate event applies only to controls on a form, not controls on a report.
The BeforeUpdate event does not apply to option buttons, check boxes, or toggle buttons in an option group. It applies only to the option group itself.
Remarks
To run a macro or event procedure when these events occur, set the BeforeUpdate property to the name of the macro or to [Event Procedure].
The BeforeUpdate event is triggered when a control or record is updated. Within a record, changed data in each control is updated when the control loses the focus or when the user presses ENTER or TAB. When the focus leaves the record or if the user clicks Save Record on the Records menu, the entire record is updated, and the data is saved in the database.
When you enter new or changed data in a control on a form and then move to another record or save the record by clicking Save Record on the Records menu, the BeforeUpdate event for the form occurs immediately after the BeforeUpdate event for the control. When you move to a different record, the Exit and LostFocus events for the control occur, followed by the Current event for the record you moved to, and the Enter and GotFocus events for the first control in this record. To run the BeforeUpdate macros or event procedures without running the Exit and LostFocus macros or event procedures, save the record by using the Save Record command on the Records menu.
BeforeUpdate macro and event procedures run only if you change the data in a control. These events don't occur when a value changes in a calculated control. BeforeUpdate macro and event procedures for a form run only if you change the data in one or more controls in the record.
For forms, you can use the BeforeUpdate event to cancel updating of a record before moving to another record.
If the user enters a new value in the control, the OldValue property setting isn't changed until the data is saved (the record is updated). If you cancel an update, the value of the OldValue property replaces the existing value in the control.
You often use the BeforeUpdate event to validate data, especially when you perform complex validations, such as those that:
- Involve conditions for more than one value on a form.
- Display different error messages for different data entered.
- Can be overridden by the user.
- Contain references to controls on other forms or contain user-defined functions.
Note To perform simple validations, or more complex validations such as requiring a value in a field or validating more than one control on a form, you can use the ValidationRule property for controls and the ValidationRule and Required properties for fields and records in tables.
A run-time error will occur if you attempt to modify the data contained in the control that fired the BeforeUpdate event in the event's procedure.
Macro
You can use BeforeUpdate macros if you want to store all the validations for a form in one macro group or if you use a validation expression on several forms.
For example, suppose you have a form on which the user enters the name of a country in a Country control and its corresponding postal code in a Postal Code control. You use conditional expressions in the macro to make sure that the data entered in the Country control corresponds to the data entered in the Postal Code control and to display a message if invalid data is entered in the Postal Code control.
You can use an AfterUpdate macro to display a different page in the form or move the focus to a particular control or record. For example, when the user enters a value in a Category control on a form, you can use the GoToPage action in an AfterUpdate macro to move the focus to the page of the form that contains the controls for that category.
You can use the CancelEvent action in a BeforeUpdate macro to cancel the update. If the BeforeUpdate macro is attached to a control, the CancelEvent action returns the focus to the control, and the data the user entered remains in the control.
If a BeforeUpdate macro is attached to a form (in which it runs each time a record is changed), the CancelEvent action returns the focus to the record.
You can't use the CancelEvent action in an AfterUpdate macro to cancel the AfterUpdate event.
Example
The following example shows how you can use a BeforeUpdate event procedure to check whether a product name has already been entered in the database. After the user types a product name in the ProductName box, the value is compared to the ProductName field in the Products table. If there is a matching value in the Products table, a message is displayed that informs the user that the product has already been entered.
To try the example, add the following event procedure to a form named Products that contains a text box called ProductName.
Private Sub ProductName_BeforeUpdate(Cancel As Integer)
If(Not IsNull(DLookup("[ProductName]", _
"Products", "[ProductName] ='" _
& Me!ProductName & "'"))) Then
MsgBox "Product has already been entered in the database."
Cancel = True
Me!ProductName.Undo
End If
End Sub