Tobin Titus

Great post, i have solved my problem. Thanks a lot.

I'm having a problem.  I have console app that creats a form to display its output unless you pass it a command line parameter telling it to run quietly.  The program runs fine until it tries to update the output form from an async callback.

The module that contains Sub Main() also contains:

   Delegate Sub OutputPrintCallback(ByVal OutputText As String)

   Public Sub OutputPrint(ByVal OutputText As String)

       If OutputForm IsNot Nothing Then OutputForm.OutputTextBox.Invoke(New OutputPrintCallback(AddressOf OutputForm.OutputPrint), New Object() {OutputText})

       If LogStream IsNot Nothing Then LogStream.Write(vbCrLf & Now.ToString("hh:mm:ss - ") & OutputText)

       Debug.Write(vbCrLf & Now.ToString("hh:mm:ss - ") & OutputText)

       Application.DoEvents()

   End Sub

and on the Log Form:

Public Class LogForm

   Public Sub OutputPrint(ByVal OutputText As String)

       OutputTextBox.Text &= vbCrLf & Now.ToString("hh:mm:ss - ") & OutputText

       OutputTextBox.SelectionStart = OutputTextBox.Text.Length

       OutputTextBox.ScrollToCaret()

   End Sub

End Class

This works well until an async thread tries to OutputPrint. Then everything just locks up.  

Everything is started from Sub Main, the form is just used for output.

OutputForm is an instance of LogForm created of the program's not running in quiet mode.

Any suggestions?

Should the Delegate be in the Form or the Module?

Very neat! I had the same wacky problem too. Since I only have one form I used .OpenForms(0) instead in my app.

If your using multiple threads you will get a first chance exception thrown if two threads want to update the same form. Use this code to check to see if you successfully pulled a reference to your form,

Public Sub UpdateStatusLabel(ByVal strMessage As String())

       Try

            Dim f As Form1 = My.Forms.Form1.ActiveForm

               If f.ActiveForm Is Nothing Then

                   Debug.Write("Nothing" & vbNewLine)

               Else

                   f.Invoke(New UpdateStatusLabelHandler(AddressOf f.UpdateStatusLabelMethod), _

                            New Object() {strMessage})

               End If

       Catch ex As Exception

       End Try

   End Sub

A forum friend used this page to explain a similar Problem for a text box not updating on a networking threaded solution. Basically, after delegating and invoking the text box - everything works like a charm now!

Thanks!

Thanks for your explanation. I was trying to figure that out for about 2 hours :)

Greets from Latvia :)

More thanks...I had tired numerous google search postings on vb.net threading and this is the only one that actually worked. All the others would have some sort of fatal flaw that caused run time errors or just plain would not compile. Even on the code posted on MSDN for VS 2005(which is what I am using) failed.

With this code, I have a program as a basis for learning about threading.

Thanks again!

Thanks Tobin!

Been googling for a over day for a solution for this problem!