At work we are using a virtual desktop manager called AltDesk
(http://www.astonshell.com/), and it is causing a weird and extremely
annoying problem with the VB.NET application I am developing.

If I start my app, open a test form using ShowDialog() (this is a
menu choice on the main app), and then switch to a different virtual
desktop, the test form immediately closes (in what seems to be an
abnormal way -- the Closing event is raised, but the Closed event
is not).  This behavior means that while a modal form is open I
can't switch to another desktop and do something different.  I think
this rather defeats the purpose of having virtual desktops!  This
behavior occurs only when a form is is opened modally -- there are
no problems when the same form is opened using Show().  I have not
seen this behavior with any other applications.

What I need to know of course is whether anyone else has seen this
behavior, whether it is a bug or a feature (in either .NET or
AltDesk), and most important, whether there is a fix or workaround.
I would be most grateful for any ideas or suggestions!

Here are some observations (note code at bottom of post):

The problem only occurs if the form is waiting for input.  If there
is code inside my test form that is grinding away doing some work
then I can switch to another desktop, and if I switch back before
the work is complete the form does not close.  However if I don't
switch back the form closes when the work is finished and the form
is ready for more input.

Note the commented code in XYZ_Closing.  If I set the DialogResult
then the Closed event *does* in fact get raised when a change of
desktop triggers a close.  If no work is done in XYZ_Closing then
the Closed event is not raised (i.e., XYZ_Close is never called).

Canceling the close in XYZ_Closing, as one would expect, makes the
form (and by extension the application) impossible to close.  That
is, until I switch to another desktop -- when I do that the form
instantly closes, just as if there had been no cancel.

And here's something really strange.  Suppose I call ShowDialog
twice in a row (see below).  And suppose that after the form pops
up for the first time I then switch to another desktop.  What
happens is that the first instance of the form closes, then when
ShowDialog() is called again the form pops up again -- this time
on the new desktop.  But strangely, although invoked using
ShowDialog(), the second form is not modal!  Perhaps relatedly,
the second instance of the form does not close if I switch to other
desktops.  The end result is that I can go back to the application,
invoke my test code again, and end up with multiple functional
copies of what ought to be a modal form.  This just seems bizarre!

Anyway, here is some skeletal code:

Dim xxx as New XYZ
xxx.ShowDialog() 'Pops up in normal way on initial desktop.
xxx.ShowDialog() 'Pops up on new desktop, and is not modal.

....

'This is my test form.
Public Class XYZ
    Inherits System.Windows.Forms.Form

    'The usual stuff, followed by some test code...

    Private Sub XYZ_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        Debug.WriteLine("Closing")

        'Me.DialogResult = DialogResult.Yes
        'Debug.WriteLine("DialogResult set to Yes")

        'e.Cancel = True
        'Debug.WriteLine("Canceled!")
    End Sub

    Private Sub XYZ_Closed(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Closed
        Debug.WriteLine("Closed")
    End Sub
End Class

John Brock wrote (in six (!) newsgroups):

Show quoteHide quoteI haven't seen that behavior, but I use MSVDM [Virtual Desktop
Manager], not AltDesk. With MSVDM, I lose popup tooltips in my
WinForms apps after switching to a different desktop and then
switching back. This happened with WinForms 1.1 and still happens in
2.0.

A customer's apps that used VS-like dockable, autohide toolwindows
(from Janus) would get horribly confused after switching desktops.

I haven't found any workaround or fix for these issues, but take
(some) comfort from the way that Excel doesn't handle virtual desktops
well, either - a maximized Excel window loses its toolbars and menus
after a desktop switch, and there doesn't seem to be any way to get
them back. The fault *seems* to lie with the virtual desktop managers
- it looks like Windows wasn't really designed to support virtual
desktops, and the managers have to play various tricks to get it to
mostly work. Perhaps vdm-s will be solider under Vista.

On 28/08/2006 in message <ecvc9u$cc***@reader2.panix.com> John Brock wrote:

If you are running it on XP have you tried it with the MS Desktop manager
which is a power toy I think? Just in case it's AltDesk causing the issue.

Serialization help needed
XML reading issue....
DataControlFieldCollection instantiated twice
Async Sockets and IOCPS
Immutable Classes