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(ByV al sender As Object, ByVal e As System.Componen tModel.CancelEv entArgs) Handles MyBase.Closing
Debug.WriteLine ("Closing")
'Me.DialogResul t = DialogResult.Ye s
'Debug.WriteLin e("DialogResu lt set to Yes")
'e.Cancel = True
'Debug.WriteLin e("Canceled!" )
End Sub
Private Sub XYZ_Closed(ByVa l sender As Object, ByVal e As System.EventArg s) Handles MyBase.Closed
Debug.WriteLine ("Closed")
End Sub
End Class
--
John Brock
jb****@panix.co m
