Re: Async delegates, illegal cross thread UI control access

That sounds odd.  IIRC, There's really only three instances where you
wouldn't get the cross-thread exception: the control hasn't fully been
created yet, CheckForIllegalCrossThreadCalls is set to false, or the
framework thinks your calling a thread-safe call.

On Thu, 29 Mar 2007 13:49:51 -0500, Ron <[email protected]> wrote:

>Hi all,
>
>I've encountered a situation where I thought VS2005 would warn me about a
>illegal cross thread UI call. I actually wanted the error to happen
because
>I'm doing a demo for my peers on the Asynchronous Programming Model.
>
>WinForms app, long running web service call of 3-5 seconds. Don't want to
>synchronously invoke the service call, and not using the asynchronous
>methods in the proxy yet.
>
>The app is demonstrating the Asynchronous Programming Model ala MSDN docs
to
>my peers.
>
>Step 1. Create a delegate to match the service call.
>
>delegate Image GetMapImageDelegate();
>
>Step 2. Create a delegate instance, invoke it
>
>void btnGetMap_Click()
>{
> GetMapImageDelegate del = new GetMapImageDelegate(GetMapImage);
> del.BeginInvoke(OnGetMapImageComplete, del);
>}
>
>Image GetMapImage()
>{
> // long running service call here
> // return image;
>}
>
>Step 3. In the callback, end the async invocation, getting the results
>
>void OnGetMapImageComplete(IAsyncResult ar)
>{
> GetMapImageDelegate del = ar.AsycnState as GetMapImageDelegate;
> Image image = del.EndInvoke(ar);
>
> // i expect this to cause the cross-thread error
> pictureBox.Image = image;
>}
>
>My understanding is that the thread in OnGetMapImageComplete is a thread
>pool thread, and therefore accessing the pictureBox control should be
>illegal. I traced the Thread.CurrentThread.ManagedThreadID in each method,
>and showed that there are two different threads: btnGetMap_Click had ID
10,
>all others were 11.
>
>I was all prepared to create yet another delegate to handle displaying the
>image with the check for InvokeRequired pattern, but if the error (cross
>thread access to UI control) doesn't exist, then...well it isnt' necessary
>to do that.
>
>Any explanation as to why this is not occuring is appreciated.