Assembly: System.Net (in System.Net.dll)
Classes that inherit from this class can override this method to perform additional tasks when the DownloadProgressChanged event occurs.
Raising an event invokes the event handler through a delegate.
The method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.Notes to Inheritors
When overriding in a derived class, be sure to call the base class’s method so that registered delegates receive the event.