gistfile1.cs

private void ItemContainerGenerator_ItemsChanged(object sender, ItemsChangedEventArgs e)
{
	Dispatcher.BeginInvoke(new ItemAddedDelegate(i =>
	{
		var item = (ListBoxItem) MainListBox.ItemContainerGenerator.ContainerFromIndex(i - 1);
		if (item == null)
			return;

		VisualStateManager.GoToState(item, "BeforeLoaded", false);
		item.Opacity = 1.0;
		VisualStateManager.GoToState(item, "AfterLoaded", true);
	}), MainListBox.Items.Count);
}