Recycling Renderers

One thing many people try to do is access an itemRenderer from outside of the list. For example, you might want to make the cell in the fourth column of the fifth row in a DataGrid turn green because you've just received new data from the server. Getting that itemRenderer instance and modifying it externally would be a huge breech of the Flex framework and component model.

To understand itemRenderers, you have to understand why they are what they are and what our intentions were when we designed them. By the way, when I say "we," I really mean the Adobe Flex engineering team. I had nothing to do with it. Anyway, suppose you have 1,000 records you want to show. If you think the list control creates 1,000 itemRenderers, you are incorrect. If the list is showing only 10 rows, the list creates about 12 itemRenderers—enough to show every visible row, plus a couple for buffering and performance reasons. The list initially shows rows 1–10. When the user scrolls the list, it may now be showing rows 3–12. But those same 12 itemRenderers are still there: no new itemRenderers are created, even after the list scrolls.