[quoted text, click to view]

At a complete guess, you're calling Invoke on the delegate rather than
on the control. However, a complete example would be better. Could you
post one?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.


--
Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet

Hi,

My complete scenario is a bit to complicated to explain, but my problem is
this:

I start a child-thread from the main thread, the child is not a
BackgroundWorker, but a Thread, since it needs to be in ApartmentState.STA
because it needs to create a Form and display some stuff. It all works
pretty well, unless an exception occurs in the child thread. The application
shows the standard error dialog to the user, and I don't want that. If an
exception occurs, I want to get (at least) the exception message over to the
main thread, and display it there. To accomplish this, I catch the excepion
in the child thread, and does an Invoke call with the string message, to the
main thread. The problem is, it does not switch to the main thread, it's
always the child (using the threads-window in VS to see that)! Very strange,
what might I be doing wrong?

regards

Carl

[quoted text, click to view]

Why? What happened when you tried?

[quoted text, click to view]

Well, one thing I notice is that you're calling ShowDialog(),
TopMost=true, and BringToFront() from within the worker thread.

You shouldn't show a UI from a different thread than the one which
created it. That could well be part of the problem. The usual idea with
worker threads is that *non*-UI work is done in the worker thread, and
all UI updates etc are passed by to the UI thread.

--
Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet

[quoted text, click to view]

Hi again,

I'm unable to create such short example, but I've tried to copy/paste the
parts of where the threading problem occurs. There are only three classes
involved, I've added comments to describe what I've tried to do.

////////////////////////////////////////////////////////////////////////
// Code in the main thread
// This code start the entire processing of the reports. This is a Form
class instance.
// The exception message should end up here, so it can be shown.
////////////////////////////////////////////////////////////////////////

private void btnPrint_Click(object sender, EventArgs e)
{
ReportsGateway.CreateReport(userLaen, arnIDs, ardIDs, true, true, this);
}

// I've tried having this callback method in the child thread, but did not
work.
// I would actually rather have it in the child thread, because others might
start
// the report processing in the future.
public void ShowThreadError(string text)
{
throw new BofException("Error generating reports." + Environment.NewLine
+ Environment.NewLine + text);
}


////////////////////////////////////////////////////////////////////////
// Code in the report helper (gateway), an in-between layer.
// This is where the child thread is created. This is a static class,
// inheriting from Object
////////////////////////////////////////////////////////////////////////

public static void CreateReport(int userLaen, int[] arnIDs, int[] ardIDs,
bool onlyPreview, bool printCase, MyBaseForm callingForm)
{
CreateMultiReport(userLaen, arnIDs, ardIDs, callingForm);
}


private static void CreateMultiReport(int userLaen, int[] arnIDs, int[]
ardIDs, MyBaseForm callingForm)
{
object[] agOb = new object[4];

agOb[0] = userLaen;
agOb[1] = arnIDs;
agOb[2] = ardIDs;
agOb[3] = callingForm;

Thread t = new Thread(ReportGenerationForm.StartProcessingReports);
t.SetApartmentState(ApartmentState.STA);
t.IsBackground = true;

ReportGenerationForm.paramObjects = agOb;

t.Start();
}



////////////////////////////////////////////////////////////////////////
// Code in the child thread
// An exception might occur here, that should be pushed up to the main
// UI thread, for nomal display. This is a Form class instance.
////////////////////////////////////////////////////////////////////////

// I've tried to declare this in the main form gui, but no difference.
public delegate void ShowErrorMessage(string text);

public static void StartProcessingReports()
{
ReportGenerationForm frm = new
ReportGenerationForm((int)paramObjects[0],
paramObjects[1] as int[], paramObjects[2] as int[], paramObjects[3]
as MyBaseForm, true, true, true);
IntPtr handle = frm.Handle;
frm.ShowPrint();
}

private void ShowPrint()
{
try
{
ShowDialog();
TopMost = true;
BringToFront();
}
catch (Exception ex)
{
// I've tried lots of different things here, for example calling
Invoke on
// the delegate, calling invoke on the calling form etc etc, but no
use.
ShowErrorMessage d = new ShowErrorMessage((_callingForm as
XXX.YYY.ReportMainthreadForm).ShowThreadError);
IntPtr handle = this.Handle;
this.Invoke(d, new string[] { ex.Message });
}
}

regards

Carl