display a modal form but keep the underlying thread processing

I have a timer in a form that triggers some processing functionality
When that gets triggered it displays a message to the user
So if the timer elapses a bunch of times i only want 1 message displayed on the screen at any time
When the message is displayed i need is to be modal
This is kind of weird but i need a modal messagebox plus i need a way to continue processing in the underlying thread
Its like a modal asynchronous call
i have no sample code
Any advice on how i could do this?
glenn_rAsked:
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MlandaTCommented:
I have a timer in a form that triggers some processing functionality
Make sure you are using a System.Threading.Timer and not a WinForms.Timer. The Threading.Time runs on a seperate thread from the UI. This will keep it running even when there is a modal UI displayed on the GUI.

So if the timer elapses a bunch of times i only want 1 message displayed on the screen at any time
Create a form level variable and give it the reference to the modal popup. The Threading.Timer will now fire a handler on a separate thread (never mind that the timer handler is sitting within the same class and file as your form :) ). In the handler, you must use an Invoke to check if the form is already displayed and handle that. Something like:
Private STTimer As System.Threading.Timer
Private NotificationForm As NotificationFormClass

Private Sub btnStart_Click(sender As Object, e As RoutedEventArgs)

	Me.STTimer = New Timer(AddressOf Me.TimerElapsed, Nothing, 1000, System.Threading.Timeout.Infinite)

End Sub

Private Sub TimerElapsed(state As Object)

	Dim message As String = String.Format("Tick Generated from {0}", Thread.CurrentThread.Name)
	Me.Dispatcher.Invoke(DirectCast(Sub() 
               'Code to check whether to display modal form or not
               If NotificationForm IsNot Nothing Then 
                      NotificationForm = New NotificationFormClass
                      NotificationForm.ShowDialog
                      'do what you want with the result etc etc
                      NotificationForm = Nothing
               End If
        End Sub, Action))

End Sub

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These articles might also give you some further insights:
http://www.abhisheksur.com/2011/03/all-about-net-timers-comparison.html
http://msdn.microsoft.com/en-us/magazine/cc164015.aspx#S4
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glenn_rAuthor Commented:
i pasted the code into a sample winforms form and am having an error with the following line "Me.Dispatcher.Invoke(DirectCast(Sub()" it cannot find the dispatcher or namespace. I pasted this within a form class. thanks
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