BeginInvoke using a Function?

Question

Hi all,

This sub works fine:

Private Sub UpdateInfo(ByVal text As String, ByVal timeStamp As DateTime)
    If Me.lstStatus.Dispatcher.Thread Is System.Threading.Thread.CurrentThread Then
        ' Do stuff with 
    Else
        Me.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Send, New Action(Of String, DateTime)(AddressOf UpdateInfo), text, timeStamp)
    End If
End Sub

But this function doesn't:

Private Function UpdateInfo(ByVal text As String, ByVal timeStamp As DateTime) As ListItem
    If Me.lstStatus.Dispatcher.Thread Is System.Threading.Thread.CurrentThread Then
        Dim l As New ListItem
        ' Do stuff with 
        Return l
    Else
        Me.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Send, New Action(Of String, DateTime)(AddressOf UpdateInfo), text, timeStamp)
        ' Above line doesn't return anything??
    End If
End Function

How do I return my listitem in above function?

Thanks!!!!!

:) Mojo

Answer 1

Use the return value of BeginInvoke method which is of type DispatcherOperation.

For more info read:

http://msdn.microsoft.com/en-us/library/ms591206.aspx

http://msdn.microsoft.com/en-us/library/system.windows.threading.dispatcheroperation.aspx

Answer 2

You should use Func rather than Action. Func has a return value you can define as ListItem

See: http://msdn.microsoft.com/en-us/library/bb549151.aspx

Answer 3

Dispatcher.BeginInvoke() is a fire-and-forget method, the delegate target runs at some later time on the UI thread. That's not good enough in your case, you need to wait until the target runs so you can get the return value. Use the Invoke() method instead:

 Return DirectCast(Me.Dispatcher.Invoke(..), ListItem)

And use Func instead of Action. Or AddressOf, the more 'natural' VB.NET way.