SilverLight 4: do I need an extra thread for BusyIndicator to work?

Hi Experts:

    I am trying to write a SilverLight 4 program that if I click a button, then the BusyIndicator will show up for 3 seconds. I tried two ways of coding in the button-click event handler.

This way didn't work (the busy indicator never show up even though the program sleep for 3 seconds).
************************************************************
BusyNote.IsBusy = true;   // set busy indicator
System.Threading.Thread.Sleep(3000);
BusyNote.IsBusy = false;
************************************************************

The following way works fine (the busy indicator shows up for 3 seconds).
******************************************************************************
BusyNote.IsBusy = true;  // set busy indicator
System.Threading.ThreadPool.QueueUserWorkItem((state) =>
  { System.Threading.Thread.Sleep(3 * 1000);
  Dispatcher.BeginInvoke(() => BusyNote.IsBusy = false); }
);
*******************************************************************************

My question is:
1. if I want to let the button event handler do a time consuming job, do I always need to make/find another thread and put the actual work inside?
2. why it didn't work in the first example? is it because the busy indicator is set in the same thread of the sleeping work?

Thank you.
huangs3Asked:
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CuteBugCommented:
If you want the button event handler to do a time consuming job, it would be better if you utilize BackgroundWorker for that and let the Busy Indicator be on the main thread.
BackgroundWorker fires an event when its work completes.
Handle that event and stop the Busy Indicator then.
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