|InfoPath Developer Reference|
Occurs after changes to a form's underlying XML document have been made but before the changes are accepted.
Version Added: InfoPath 2003
expression An expression that returns a DataDOM object.
|pDataDOMEvent||Required||DataDOMEvent||An event object that is used during Microsoft Office InfoPath 2007 data validation events.|
This event handler allows users to cancel an operation.
During the OnBeforeChange event, the form's underlying XML document is placed in read-only mode. If the ReturnStatus property of the DataDOMEvent object is set to False, Office InfoPath 2007rejects the changes that were made and a message box is displayed to the user. If an error occurs in the scripting code for the OnBeforeChange event handler, InfoPath rejects the changes and restores the data to its previous state.
- It is best to avoid switching views during the OnBeforeChange event; changes have not yet been accepted, and switching to another view may result in an error.
- In some cases, events related to changes in a form's underlying XML document may occur more than once. For example, when existing data is changed, an insert and delete operation occurs.
- If a validation error is encountered in any OnBeforeChange event handler, the document fails to load. A
block in the **[OnLoad](bb229737\(v=office.12\).md)** event can be used to catch this validation failure and to load the document despite the error.
In the following example, the OnBeforeChange event handler is used to validate the data in a field. If the data is not valid, the ReturnStatus property of the DataDOMEvent object is used to reject the changes.