This post goes over the basics of writing a very simple custom layout that supports virtualization in spark. It assumes that you have already built a custom layout that handles the real (non-virtual) case and are comfortable doing so.
Continue reading Learn how to create a simple virtual layout in Flex 4
ItemRenderer has logic built in that changes between some standard states like normal, hovered, selected, etc. You can supplement this logic by overriding ItemRenderer.getCurrentRendererState(), or do away with the built in states altogether by subclassing DataRenderer instead of ItemRenderer.
Continue reading Using DataRenderer to add custom states to a spark List renderer
I recently created a form in Flex that required using multiple DropDownLists with a custom item renderer that loads in preview images of each item. This was really easy to do initially, but I noticed a couple performance issues that bothered me. I decided to improve the performance by implementing a simple caching strategy.
Continue reading Caching images loaded from a spark item renderer
The spark List component in Flex 4 has virtualization enabled by default. Virtualization is an optimization that only renders items that are currently in view which allows the List to support very large data sets. You can learn more about how virtualization works in Flex 4 by reading the Spark Virtualization Spec.
Continue reading Performance implications of the List itemRenderer vs. itemRendererFunction properties