Synchronous Before event that occurs when an existing item is changed, for example, when the user changes data in one or more fields.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
The ItemUpdating event can be used in response, for example, to a form edit, a datasheet post, an object model call, or a Web service call.
When you add a new item, only the ItemAdding() event is raised. However, in cases where Explorer View is used, both the ItemAdding and ItemUpdating events are raised. In such cases the ItemUpdating event always occurs after the ItemAdding() event occurs.
When a Boolean column value in a list is set to true and the ItemUpdating method is called, the AfterProperties property reports -1 as the value instead.