Me.Invoke in VB.NET doesn't actually "Invoke" - threads stall on Invoke statement

Question

I've got the following code:

Public Delegate Sub SetStatusBarTextDelegate(ByVal StatusText As String)
Private Sub SetStatusBarText(ByVal StatusText As String)
    If Me.InvokeRequired Then
        Me.Invoke(New SetStatusBarTextDelegate(AddressOf SetStatusBarText), StatusText)
    Else
        Me.labelScanningProgress.Text = StatusText
    End If
End Sub

The problem is that, when I call the "SetStatusBarText" sub from another thread, InvokeRequired is True (as it should be), but then my threads stall on the Me.Invoke statement - pausing execution shows them all just sitting there, not actually invoking anything.

Any thoughts about why the threads seem to be afraid of the Invoke?

Answer 1

The Invoke method puts a message in the message queue to perform the method call in the main thread. This means that you need a main thread with a message pump. If the main thread is busy, or if you are doing this in an application without a message pump (e.g. a console application), the message will just remain in the queue.