Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal _
  e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
 
        grafik = Me.CreateGraphics()
        grafik.DrawLine(Pens.Black, (rand_links + 20), (rand_oben + 10), ( _
          rand_rechts - 10), (rand_unten - 10))
 
End Sub