System.ComponentModel.PropertyChangingEventHandler is introduced in the .NET Framework version 3.5. For more information, see The .NET Framework 3.5 Architecture.

When you create a System.ComponentModel.PropertyChangingEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event-handler delegates, see Events and Delegates.