Do I need to use Invoke when calling async method with Task.Run?

Question

I have a problem with one of the events from a DLL, and I've decided to move some code to a separate Sub and make that call async (with a delay):

Public Async Sub DeskoScan()


  ListAdd("Perform scan START.")
  Try

    If _Duplex AndAlso _firstImageFileUploaded Then
      Await Task.Delay(1000) ' here I want to be sure that all things related to the previous scanning process are closed
      Dim Aborted As Boolean
      Using frm = New countingForm
        frm.lblTime.Text = _My_Settings.Item("WaitForDialog").Value
        frm.lblMessage.Text = "Flip Document For Second Page Scan" _
                  + vbCrLf + " - press OK when ready, or wait for count down to 0" _
                  + vbCrLf + " - press Retry for another " + _My_Settings.Item("WaitForDialog").Value + " seconds" _
                  + vbCrLf + " - press Abort to just cancel it"

        frm.btnRetry.DialogResult = DialogResult.None
        Aborted = frm.ShowDialog(Me) = DialogResult.Abort
      End Using

      If Aborted Then
        Exit Sub
      End If
    End If

    _deviceThread.Execute(Sub(ByVal device As Desko.Scan.Device)
                            device.Snapshot.Reset()
                            device.Snapshot.Infrared.Enabled = False
                            device.Snapshot.Infrared.Flags = Desko.Scan.ScanFlags.None
                            device.Snapshot.Infrared.ShutterWidthFactor = 1
                            device.Snapshot.Visible.Enabled = True
                            device.Snapshot.Visible.Flags = Desko.Scan.ScanFlags.DocumentClipping Or Desko.Scan.ScanFlags.AmbientFilter
                            device.Snapshot.Visible.ShutterWidthFactor = 1
                            device.Snapshot.Ultraviolet.Enabled = False
                            device.Snapshot.Ultraviolet.Flags = Desko.Scan.ScanFlags.None
                            device.Snapshot.Ultraviolet.ShutterWidthFactor = 1
                            device.Snapshot.Resolution = Desko.Scan.Resolution.Full
                            device.Snapshot.Perform()
                          End Sub)

  Catch ex As Exception
    ListAdd(ex.ToString())
  End Try
End Sub

And because the procedure is run in a separate thread apart from the main one, I call it like this:

    If Me.InvokeRequired Then
      Me.Invoke(Sub() DeskoScan())
    Else
      DeskoScan()
    End If

Now in that event, I want to call that code but to make an async call, like this:

Private Sub HandleSnapshotCompleted(ByVal sender As Object, ByVal args As Desko.Scan.SnapshotCompletedEventArgs)

  If _Duplex AndAlso _firstImageFileUploaded Then

    Task.Run(Sub() DeskoScan()) 'Is this enough or do I need Me.Invoke too?

  Else
    ListAdd("Snapshot completed. You may remove the document.")
    Minimize()
  End If

End Sub

My question is do I need here Invoke call or Task.Run is enough? (I can't test this code because I am missing a scanner)

UPDATE

Yes Craig you are right I don't need Task.Run here, but I need async await Sub so I can make sure that all event handlers on scanner objects are processed. By doing Await Task.Delay(2000) I will make the Sub asynchronous.

  Public Async Sub DeskoScan()
    If Me.InvokeRequired Then
      Me.Invoke(Sub() DeskoScan())
    Else
      Await Task.Delay(2000)
      ....
    End If
  End Sub

Do I need to use Invoke when calling async method with Task.Run?

Answers (1)

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