ItemContainerGenerator without index

Question

I create a inheritor from Panel class and need to realize items. I use this code:

    protected UIElement RealizeItem(int itemIndex)
    {
        var generator = ItemContainerGenerator;
        var position = generator.GeneratorPositionFromIndex(itemIndex);
        using (generator.StartAt(position, GeneratorDirection.Forward, true))
        {
            var isNewlyRealized = false;
            var container = generator.GenerateNext(out isNewlyRealized) as UIElement;
            if (position.Offset != 0 && container != null && isNewlyRealized)
            {
                container.SetValue(IndexForItemContainerProperty, itemIndex);
                InsertInternalChild(position.Index + 1, container);
                generator.PrepareItemContainer(container);
            }
            return container;
        }
    }

This methods use ItemSource indexer for generate item. But i need to generate item from object. That is i get a list of object and need to generate item. How can i do this?