I guess this week is my week for creating AS3/Flex hacks. I created an XML encoder/decoder that will accept a class-map and create your model from your XML and visa-versa. As part of that I have display objects as part of the model that needs saving out. I suppose you could liken it to MXML.

In order for the XML encoder to work with DisplayObjectContainers I had to give it a way to work with an ArrayCollection to add or remove the children. So I subclassed LayoutContainer and gave it a property called “children” which is an ArrayCollection. Then I set up as a listener to it and every time something is added or removed I use the corresponding DisplayObjectContainer methods to update the display. Pretty slick! The only downside is that someone could add anything to the children ArrayCollection and break things since I am expecting DisplayObjects only. I could add error checking and make it fix itself when that happens… maybe another time.

Here’s my listener which responds to the “collectionChange” event of children:

protected function onChildrenChange(event:CollectionEvent):void
{
	var i:Number;
	var items:Array = event.items;
	var location:Number = event.location;
	var oldLocation:Number = event.oldLocation;
	var numItems:Number = items.length;
	var child:DisplayObject;
	var propChange:PropertyChangeEvent;

	switch (event.kind)
	{
		case CollectionEventKind.ADD:
			for (i = 0; i < numItems; i++)
			{
				child = items[i] as DisplayObject;
				if (child)
					addChildAt(child, location + i);
			}
			break;

		case CollectionEventKind.REMOVE:
			for (i = 0; i < numItems; i++)
			{
				child = items[i];
				if (child)
					removeChild(child);
			}
			break;

		case CollectionEventKind.MOVE:
			setChildIndex(getChildAt(oldLocation), location);
			break;

		case CollectionEventKind.REPLACE:
			for (i = 0; i < numItems; i++)
			{
				propChange = items[i] as PropertyChangeEvent;
				var oldChild:DisplayObject = propChange.oldValue as DisplayObject;
				var newChild:DisplayObject = propChange.newValue as DisplayObject;
				if (oldChild && newChild)
				{
					var index:Number = getChildIndex(oldChild);
					removeChildAt(index);
					addChildAt(newChild, index);
				}
			}
			break;

		case CollectionEventKind.REFRESH:
			removeAllChildren();
			for each (child in _children)
				addChild(child);
			break;

		case CollectionEventKind.RESET:
			removeAllChildren();
			for each (child in _children)
				addChild(child);
			break;

		case CollectionEventKind.UPDATE:
			// don't need to do anything
			break;
	}
}