Ever since Flex came out people have been after similar functionality for Flash. There aren’t many options out there, but a few worth mentioning are http://www.soundstep.com/blog/downloads/baseui/ and http://www.nbilyk.com/flash-layout-manager. After studying these (great) diferent approaches, I decided to give it a try and build my own version, similarities not a coincidence.
LayoutManager and LayoutElement
LayoutElement extends a DisplayObject’s size and positioning properties. Both size and position can be specified in pixels or percentage of a container. LayoutManager manages LayoutElements and updates them as necessary.
LayoutContainer extends Flash’s UIComponent and works much like ScrollPane, except it’s content can be added/removed directly just like any other DisplayObjectContainer.
Layouts Containers, such as Canvas, HBox and VBox, extends from the LayoutContainer class and add LayoutManager and LayoutElement functionality.