Chapter 2. Containers
The Flex Framework provides two sets of containers: MX and Spark. The
introduction of the Spark architecture to the Flex 4 SDK offers a level of
abstraction between containers and layouts not available in the MX
architecture. An MX container internally manages the size and position of
its children based on specified properties and styles. To modify the layout
rules of a MX container, you often create a subclass of a similar container
or the base mx.core.Container class and
override methods such as updateDisplayList() and measure(). In contrast, Spark containers are
separated from layout management and allow for a developer to specify
layouts available in the spark.layouts
package or create custom LayoutBase-based
layouts to manage the size and position of child elements. The separation of
responsibilities for Spark containers provides enhanced runtime performance
in rendering because layout is handled through delegation.
Included in the Spark layout container architecture are two base
classes, GroupBase and SkinnableContainerBase. Both handle visual
elements, but only the latter provides skinning capabilities for the
container. The spark.components.Group and
spark.components.DataGroup classes are
extensions of GroupBase; both are
non-skinnable containers, but they differ in how child elements are declared
and represented on their display lists. A Group container holds children that are
implementations of IVisualElement and that are added either through MXML ...
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