vb.net How to update UI from task

Make your Downloads class raise a custom event with the text to display in the label:  

Public Class Downloads

    Public Event Status(ByVal txt As String)

    Private Sub Foo()
        RaiseEvent Status("blah...") ' <-- just an example
    End Sub

End Class

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Now, in your form, create a method to receive the event and update the label:  

Public Class Form1

    Private Sub dld_Status(ByVal txt As String)
        If Me.InvokeRequired Then
            Me.Invoke(New Action(Of String)(AddressOf dld_Status), New Object() {txt})
        Else
            Me.lblStatus.Text = txt
        End If
    End Sub

End Class

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Finally, use AddHandler() to wire up the event when the instance of Downloads is created:  

...
        Dim d As New Downloads
        d.ThreadName = "t" & CStr(threadCount)
        AddHandler d.Status, AddressOf dld_Status
        Dim t As Task = Task.Factory.StartNew(Sub() d.DownloadPatientData(v))

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Well this compiles but the code never gets to the  Me.lblStatus.Text = txt
It does the Me.Invoke section but nothing else.

The method to recieve the event inthe main form should be:

Public Class Form1

    Private Sub dld_Status(ByVal txt As String)
        If Me.InvokeRequired Then
            Me.Invoke(New Action(Of String)(AddressOf dld_Status), New Object() {txt})
        End If
        Me.lblStatus.Text = txt
    End Sub

End Class

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that doesn't work either. Never gets to lblstatus.text = txt

I have also noticed that raising the event from the DownloadPatientData method, even though it doesn't update the label, prevents the application from closing.  It gets stuck in the task.waitall call. Removing the raiseevent allows it to complete as normal.

There must be a different way to update the gui using tasks.

This is the complete code in the main form.  When the tasks complete I close the app.

 While VendorQueue.Count > 0
                Dim v As Vendor = Nothing

                If VendorQueue.TryDequeue(v) = True Then
                    threadCount += 1
                    Console.WriteLine("Processing Org " & v.Org)
                    v.DrFirstVersion = DrFirstVersion
                    Dim d As New Downloads
                    d.ThreadName = "t" & CStr(threadCount)
                    d.MyVendor = v
                    AddHandler d.ThreadFinished, AddressOf ThreadUpdateHandler
                    '  lstTasks.Add(Task.Factory.StartNew(Sub() d.DownloadPatientData()))
                    Dim t As New Task(Sub() d.DownloadPatientData())
                    t.Start()
                    lstTask.Add(t)
                End If
            End While

            Task.WaitAll(lstTasks.ToArray)

            Application.Exit()





I understand what you are saying. A catch 22.  So what is the alternative?