Question

I have a method that is asynchronously called when System.Net.Sockets.NetworkStream.BeginRead completes.

 skDelegate = New AsyncCallback(AddressOf skDataReceived)
 skStream.BeginRead(skBuffer, 0, 100000, skDelegate, New Object)

In that callback method, I need to interact with the UI thread.

Sub skDataReceived(ByVal result As IAsyncResult)
    CType(My.Application.OpenForms.Item("frmMain"), frmMain).refreshStats(d1, d2)
End Sub

This causes an exception after the method completes. (when End Sub is executed)

The Undo operation encountered a
context that is different from what
was applied in the corresponding Set
operation. The possible cause is that
a context was Set on the thread and
not reverted(undone).

So how do I interact with the UI thread from the callback method? What am I doing wrong?

Answer 1

You have to use Invoke or BeginInvoke on the frmMain object to enqueue a message (a delegate) to execute on the UI thread.

Here’s how I’d do it in C#.

frmMain.Invoke(() => frmMain.refreshStats(d1, d2));

Also check this list of Invoke types and their uses.