Help with Events, Delegates and Threading

[Rymfax]

I was hoping someone could help me figure something.

I have a class that is a downloader and I've created some events on it
so that a Windows Form can use those to be notified when to update
screen information. The problem I'm running into is that when the
downloader runs on a different thread and those Events fire, if the
corresponding method on the GUI for that even updates any Controls, I
get a threading error. I know that I can solve this by using
delegates on my Windows Form, but I was wondering if there was any way
to code the downloader object so that the delegates were taking care
of on that side. I only ask because I think if you use the
BackgroundWorker and call the ReportProgress() method that the
corresponding method for the event on the Windows Form can update
Controls just fine. How is it able to do that?

Any help would be appreciated.

Thanks!

[Peter Duniho]

On Mon, 04 Aug 2008 11:12:37 -0700, Rymfax <cw*****@bigbangllc.comwrote:

[...] I was wondering if there was any way
to code the downloader object so that the delegates were taking care
of on that side. I only ask because I think if you use the
BackgroundWorker and call the ReportProgress() method that the
corresponding method for the event on the Windows Form can update
Controls just fine. How is it able to do that?

I believe that it captures the SynchronizationContext for the thread used
to initialize the BackgroundWorker instance, and then uses the context to
invoke delegates on the correct thread. You could to that.
Alternatively, you can traverse the invocation list for the event
explicitly, checking the Target for each Delegate instance to see if it
implements ISynchronizeInvoke and use that to call Invoke() (but this will
only work if the delegate references a member of a GUI element inheriting,
for example, Control).

Personally, it's my opinion that GUI code should know about GUI stuff and
worker code should not. This means that it's the event _handler_ that
should deal with the threading issue as necessary, rather than your
downloader class. Note that with anonymous methods, creating the delegate
to be invoked on the GUI thread is very concise and elegant (in my
opinion).

Pete