The TaskId property returns the task ID associated with the
last background task that started. The value of this property is only
meaningful after the AsyncGetFile or AsyncPutFile method
is called to initiate a background file transfer, and the value will
change with each subsequent background transfer that is performed. If
this property returns a value of zero, that indicates that no
background tasks have been started for this instance of the control.
To enumerate the active background tasks, use the TaskCount
property and the TaskList property array.