Expanding item renderers in a DataGroup or List

The spark DataGroup component is designed to take data items and pass them through an item renderer to create a visual representation of that data. In Flex 4 it is very easy to build custom item renderers.

This sample application demonstrates how you can create an item renderer that only shows some information by default and allows the user to drill down to see more information by clicking on an item or it’s associated “twisty” icon.

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Performance implications of the List itemRenderer vs. itemRendererFunction properties

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.
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Introduction to the DataGroup Component in Flex 4

DataGroup is a new component introduced in Flex 4 that is responsible for turning data items like Strings and Objects into visual elements. The process of turning boring old data items into a visual representation is called item rendering. DataGroup is the lightest weight component that deals with item rendering. It has no skin and no concept of selection. A SkinnableDataContainer is exactly the same as a DataGroup except it has a skin and a List provides selection functionality.
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