private void ModelStarChangedEventHandler(object sender, StarChangedEventArgs e)
 {
     if (e.isDisappeared && _stars.ContainsKey(e.Point))
     {
         FrameworkElement starControl = _stars[e.Point];
         _sprites.Remove(starControl);
     }
     else
     {
         if (!_stars.ContainsKey(e.Point))
         {
             FrameworkElement starControl = InvadersHelper.StarControlFactory(e.Point, Scale);
             _stars[e.Point] = starControl;
             _sprites.Add(starControl);
         }
         else
         {
             FrameworkElement starControl = _stars[e.Point];
             InvadersHelper.SetCanvasLocation(starControl, e.Point.X * Scale, e.Point.Y * Scale);
         }
     }
 }