Handles the synchronous event that occurs before an item is added.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Available in Sandboxed Solutions: Yes
Available in SharePoint Online
This event occurs in the following situations:
Default data is populated from a template.
New items are created using the browser user interface.
New items are added using the object model or Web service.
When adding a new document to a document library, do not use the property setting Status=CancelNoError to cancel this event, since doing so redirects the user to the "File not found" error.