Imports System.Threading

Public Class Window107
  Private Async Sub btnRun_Click(sender As Object, e As RoutedEventArgs) Handles btnRun.Click
    Halt = False
    Nr = 0
    Do
      Await Task.Run(New Action(AddressOf DisplaySegmentTask))
      GenerateNextSegment()
    Loop Until Halt
  End Sub

  Private Halt As Boolean
  Private rnd As New Random
  Private Nr As Integer
  Private rec As Rectangle

  Private Sub DisplaySegmentTask()
    Dispatcher.Invoke(New Action(Sub()
                                   If rec IsNot Nothing Then cv.Children.Add(rec)
                                 End Sub))
    Thread.Sleep(1000)
  End Sub

  Private Sub GenerateNextSegment()
    rec = New Rectangle With {.Width = 100, .Height = 50, .Fill = Brushes.Red}
    Canvas.SetLeft(rec, rnd.Next(5, 300))
    Canvas.SetTop(rec, rnd.Next(5, 400))
    Nr += 1
    Halt = Nr = 10
  End Sub

End Class