Cancels a pending asynchronous operation.
Assembly: System (in System.dll)
When you call , your application still receives the completion event associated with the operation. For example, when you call to cancel a DownloadStringAsync operation, if you have specified an event handler for the DownloadStringCompleted event, your event handler receives notification that the operation has ended. To learn whether the operation completed successfully, check the Cancelled property on the base class of DownloadDataCompletedEventArgs in the event data object passed to the event handler.
If no asynchronous operation is in progress, this method does nothing.