problem with System.InvalidOperationException - enabling buttons from within event sub

abiemann

I don't know why I'm getting this InvalidOperationException - so I'm really eager to find an explanation and learn from this bug. the code:

Imports myprog.Control_DataCapsule 'this is a control containing several text boxes and buttons
Class Window1
Private MSVMobject As ClassMSVM = Nothing

Private Sub Window1\_Loaded()

    Try
        MSVMobject = New ClassMSVM
        AddHandler MSVMobject.VMexited, AddressOf Me.MSVM\_VMexited
    Catch
        MsgBox("MSVM is not available on this machine.")
    End Try

End Sub

Friend Sub MSVM\_VMexited()
    .
    .
    .
    Dim OdataCapsule As Control\_DataCapsule 'causes an invalidOperationException
    .
    .
    .
End Sub

Private Sub StackPanel\_ButtonClick(ByVal sender As Object, ByVal e As RoutedEventArgs)

    MSVMobject.StartVM()

End Sub

End Class

Public Class ClassMSVM

Public Event VMexited()

Public Sub StartVM()
        .
        .
        .
        Dim myProcess As Process = New Process()
        myProcess.StartInfo.FileName = strStartupPath + "vmconnect.exe"
        myProcess.StartInfo.Arguments = "localhost " + VMname
        myProcess.StartInfo.WindowStyle = ProcessWindowStyle.Hidden
        myProcess.StartInfo.CreateNoWindow = True
        myProcess.EnableRaisingEvents = True
        AddHandler myProcess.Exited, AddressOf Me.VMconnectExited
        myProcess.Start()
End Sub

Friend Sub VMconnectExited(ByVal sender As Object, ByVal e As System.EventArgs)

    Dim myProcess As Process = DirectCast(sender, Process)
    myProcess.Close()

    'trigger event that will be captured in Window1.xaml.vb
    RaiseEvent VMexited()

End Sub

End Class

'in a separate vb file...
Partial Public Class Control_DataCapsule

'member variables
Public m\_iIndexInList As Integer

Public Sub New()
    ' This call is required by the Windows Form Designer.
    InitializeComponent()

    m\_iIndexInList = 0
End Sub
'\*\*\* SET \*\*\*
Public Sub SetTitle(ByVal strTitle As String)
    Me.TextBoxTitle.Text = strTitle
End Sub
.
.
.

End Class

What happens is that after I click a button in my stackpanel, MSVM is launched. This works great. Once I close MSVM, the MSVM_VMexited() sub starts to execute but as soon as it gets to "Dim OdataCapsule As Control_DataCapsule" an I

abiemann

what I've done now is declare OdataCapsule as a member variable of Window1 (temporarily called it "myOdataCapsule" for this experiment), and the program gets farther... however, now the following fails:

myOdataCapsule = DirectCast(Me.StackPanel1.Children.Item(iSPindex), Control_DataCapsule)

myOdataCapsule always equals Nothing ! This is a problem since I used the DirectCast to gain access to methods in Control_DataCapsule (many of these are stored in the stackpanel) to enable and disable buttons on the controls. Overall goal Somehow I need to step through the Control_DataCapsule's in the stackpanel once Window1 receives the VMexited event. My implementation above is the only way I thought I could :((

abiemann

I then decided an alternative might be just to disable and enable the stackpanel on the Window1

Private Sub StackPanel\_ButtonClick(ByVal sender As Object, ByVal e As RoutedEventArgs)
    Me.StackPanel1.IsEnabled = False 'instead of individually disabling buttons in each control on the stackpanel
    MSVMobject.StartVM()
End Sub

Friend Sub MSVM\_VMexited()
    Me.StackPanel1.IsEnabled = True
End Sub

However, "Me.StackPanel1.IsEnabled = True" still caused the exception X| :(( :confused:

Luc Pattyn

Hi, I'm not familiar with RaiseEvent as I work mainly in C#, however it seems to me you are having a typical invalid cross-thread situation: the VM signals its exit on some thread (probably a ThreadPool thread) because it is fully asynchronous and MS didn't want to force it onto the main thread. So IMO you need the same Control.InvokeRequired/Control.Invoke stuff you would need when trying to access some Control from a secondary thread, see here[^]. BTW: I don't really believe Dim OdataCapsule As Control_DataCapsule was ever throwing an exception as this statement is purely declarative, there is nothing executing there. :)

Luc Pattyn

Have a look at my entry for the lean-and-mean competition; please provide comments, feedback, discussion, and don’t forget to vote for it! Thank you.

Local announcement (Antwerp region): Lange Wapper? Neen!

abiemann

Hi Luc, I've tried it, but WPF seems to be different because I get the error: InvokeRequired' is not a member of 'System.Windows.Controls.StackPanel so I'll try something like this: http://blog.somecreativity.com/2008/01/10/wpf-equivalent-of-invokerequired/[^]

Luc Pattyn

As I am unexperienced in WPF, I won't be able to help you. Sorry. :)

Luc Pattyn

Have a look at my entry for the lean-and-mean competition; please provide comments, feedback, discussion, and don’t forget to vote for it! Thank you.

Local announcement (Antwerp region): Lange Wapper? Neen!