在Flex/AS3中,如何使用getDefinitionByName获取嵌入式资产的类定义

[Embed(source="assets/MyAsset.swf", mimeType="application/octet-stream")]
private var MyAssetClass:Class;

var assetClass:Class = getDefinitionByName("MyAsset") as Class;

var assetInstance:DisplayObject = new assetClass() as DisplayObject;
addChild(assetInstance);