ListBox.BeforeUpdate Event (Access)
The BeforeUpdate event occurs before changed data in a control or record is updated.
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.
To run a macro or event procedure when this event occurs, set the BeforeUpdate property to the name of the macro or to [Event Procedure].
This event does not apply to option buttons, check boxes, or toggle buttons in an option group. It applies only to the option group itself.
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 AfterUpdate event for the form occur immediately after the AfterUpdate 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 AfterUpdate macro or event procedure without running the Exit and LostFocus macros or event procedures, save the record by using the Save Record command on the Records menu.
BeforeUpdate macros and event procedures run only if you change the data in a control. This event does not occur when a value changes in a calculated control. BeforeUpdate macros 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.
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.
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.