Viewstack in Flex 4?

// -----------------------------------------------------------
// CBViewStack.as
// -----------------------------------------------------------
 
/**
 * Copyright (c) 2009 Todd Anderson. All Right Reserved.
 * 
 * Code provided has not been tested in a production environment
 * and should be used by another party at their own risk. I disclaim any
 * and all responsibility for any loss or damage of property that may occur
 * from using it.
 * 
 * ===================================
 * custardbelly.com
 */
package com.custardbelly.container
{
	import mx.core.IVisualElement;
 
	import spark.components.BorderContainer;
	import spark.components.SkinnableContainer;
	import spark.core.IViewport;
	import spark.events.IndexChangeEvent;
 
	/**
	 * Dispatched on change to selectedIndex property value. 
	 */
	[Event(name="change", type="spark.events.IndexChangeEvent")]
 
	/**
	 * Basic implementation of a ViewStack container targeting the Spark environment.
	 * CBViewStack inherently supports deferred instantiation. All methods and properties
	 * have been made protected in order to subclass and implement any desired creation 
	 * policy.
	 * 
	 * Child content cannot be added in markup due to the black-boxing of the mxmlContent and 
	 * mxmlContentFactory properties and corresponding methods. As such, supply content to the
	 * CBViewStack using the <b>content</b> property. The <b>content</b> property is an array
	 * of declared IVisibleElement instances.
	 * 
	 * To enable scrolling of content added to the display list of CBViewStack, it is recommended
	 * the either programatically control the viewport with an external scrollbar or wrap the 
	 * container in a <s :Scroller> instance.
	 * 
	 * The <b>content</b> and <b>selectedIndex</b> properties can be set in-line in MXML.
	 * The <b>selectedChild</b> property can only be set within ActionScript.
	 */
	[Event(name="change", type="spark.events.IndexChangeEvent")]
	[DefaultProperty("content")]
	public class CBViewStack extends BorderContainer
	{
		/**
		 * Represents the collection of IVisualElement instances to be displayed. 
		 */
		[ArrayElementType("mx.core.IVisualElement")]
		protected var _content:Array;
		/**
		 * The index within the colleciton of IVisualElements to be added to the display list. 
		 */
		protected var _selectedIndex:int = -1;
		/**
		 * Represents the current IVisualElement on the display list. 
		 */
		protected var _selectedChild:IVisualElement
 
		/**
		 * Held value for selectedIndex.
		 */
		protected var _pendingSelectedIndex:int = -1;
 
		/**
		 * @private 
		 * 
		 * Override to update selectedIndex and subsequently content on the display list.
		 */
		override protected function commitProperties() : void
		{
			super.commitProperties();
			// if pending change to selectedIndex property.
			if( _pendingSelectedIndex != -1 )
			{
				// commit the change.
				updateSelectedIndex( _pendingSelectedIndex );
				// set pending back to default.
				_pendingSelectedIndex = -1;
			}
		}
 
		/**
		 * Updates the selectedIndex value and subsequent display. 
		 * @param index int The value representing the selected child index within the content property.
		 */
		protected function updateSelectedIndex( index:int ):void
		{
			// store old for event.
			var oldIndex:int = _selectedIndex;
			// set new.
			_selectedIndex = index;
 
			// remove old element.
			if( numElements > 0 ) 
				removeElementAt( 0 );
 
			// add new element.
			selectedChild = _content[_selectedIndex];
			addElement( _selectedChild );
 
			// dispatch index change.
			dispatchEvent( new IndexChangeEvent( IndexChangeEvent.CHANGE, false, false, oldIndex, _selectedIndex ) );
		}
 
		/**
		 * Returns the elemental index of the IVisualElement from the content array. 
		 * @param element IVisualElement The IVisualElement instance to find in the content array.
		 * @return int The elemental index in which the IVisualElement resides. If not available returns -1.
		 * 
		 */
		private function getElementIndexFromContent( element:IVisualElement ):int
		{
			if( _content == null ) return -1;
 
			var i:int = _content.length;
			var contentElement:IVisualElement;
			while( --i > -1 )
			{
				contentElement = _content[i] as IVisualElement;
				if( contentElement == element )
				{
					break;
				}
			}
			return i;
		}
 
		[Bindable]
		/**
		 * Sets the array of IVisualElement instances to display based on selectedIndex and selectedChild.
		 * CBViewStack inherently supports deferred instantiation, creating and adding only IVisualElements
		 * that are requested for display. 
		 * @return Array
		 */
		public function get content():Array /*IVisualElement*/
		{
			return _content;
		}
		public function set content( value:Array /*IVisualElement*/ ):void
		{
			_content = value;
			// update selected index based on pending operations.
			selectedIndex = _pendingSelectedIndex == -1 ? 0 : _pendingSelectedIndex;
		}
 
		[Bindable]
		/**
		 * Sets the selectedIndex to be used to add an IVisualElement instance from the content property
		 * to the display list. 
		 * @return int
		 */
		public function get selectedIndex():int
		{
			return _pendingSelectedIndex != -1 ? _pendingSelectedIndex : _selectedIndex;
		}
		public function set selectedIndex( value:int ):void
		{
			if( _selectedIndex == value ) return;
 
			_pendingSelectedIndex = value;
			invalidateProperties();
		}
 
		[Bindable]
		/**
		 * Sets the selectedChild to be added to the display list form the content array.
		 * SelectedChild can only be set in ActionScript and will not be properly updated
		 * if added inline in MXML declaration. 
		 * @return IVisualElement
		 */
		public function get selectedChild():IVisualElement
		{
			return _selectedChild;
		}
		public function set selectedChild( value:IVisualElement ):void
		{
			if( _selectedChild == value ) return;
 
			// if not pending operation on selectedIndex, induce.
			if( _pendingSelectedIndex == -1 )
			{
				var proposedIndex:int = getElementIndexFromContent( value );
				selectedIndex = proposedIndex;
			}
			// else just hold a reference for binding update.
			else _selectedChild = value;
		}
	}
}
</s>

<s :Application 
	xmlns:fx="http://ns.adobe.com/mxml/2009" 
	xmlns:s="library://ns.adobe.com/flex/spark" 
	xmlns:mx="library://ns.adobe.com/flex/mx" 
	xmlns:container="com.custardbelly.container.*" viewSourceURL="srcview/index.html">
 
	<fx :Declarations>
		</fx><fx :String id="lorem">Lorem ipsum dolor sit amet consectetur adipisicing elit.</fx>
 
 
	<fx :Script>
		< ![CDATA[
			private function changeIndex():void
			{
				var index:int = viewstack.selectedIndex;
				index = ( index + 1 > viewstack.content.length - 1 ) ? 0 : index + 1;
				viewstack.selectedIndex = index;
			}
		]]>
	</fx>
 
	</s><s :layout>
		<s :VerticalLayout />
	</s>
 
	<container :CBViewStack id="viewstack" width="300" height="300" 
						   skinClass="com.custardbelly.skin.CBScrollableSkin">
		<s :Group id="child1" 
				 width="800" height="100%" 
				 clipAndEnableScrolling="true">
			</s><s :layout>
				<s :VerticalLayout horizontalAlign="justify" />
			</s>
			<s :Button label="top" />
			<s :Button label="bottom" bottom="0" />
 
		<s :Panel id="child2" 
				 width="100%" height="200" 
				 title="Child 2">
			</s><s :Scroller>
				</s><s :Group width="100%" height="100%">
					</s><s :layout>
						<s :VerticalLayout horizontalAlign="center" />
					</s>
					<s :Button label="panel button 1" />
					<s :Button label="panel button 2" />
 
 
 
		<s :DataGroup id="child3" 
					 width="100%" height="100%"
					 itemRenderer="spark.skins.spark.DefaultItemRenderer">
			</s><s :layout>
				<s :VerticalLayout />
			</s>
			<s :dataProvider>
				<s :ArrayCollection source="{lorem.split(' ')}" />
			</s>
 
	</container>
 
	<s :Button label="switch index" click="changeIndex();" />
 
	<s :HGroup>
		<s :Button label="select child 1"
				  enabled="{viewstack.selectedChild != child1}"
				  click="{viewstack.selectedChild = child1}" 
				  />
		<s :Button label="select child 2"
				  enabled="{viewstack.selectedChild != child2}"
				  click="{viewstack.selectedChild = child2}" 
				  />
		<s :Button label="select child 3"
				  enabled="{viewstack.selectedChild != child3}"
				  click="{viewstack.selectedChild = child3}" 
				  />
	</s>