flex4/flash builder中动态加载Module并与之交互的正确方式

<?xml version="1.0" encoding="utf-8"?>
<mx:Module xmlns:fx="http://ns.adobe.com/mxml/2009" 
		   xmlns:s="library://ns.adobe.com/flex/spark" 
		   xmlns:mx="library://ns.adobe.com/flex/mx" layout="absolute" width="200" height="200">
	
	<fx:Script>
		<![CDATA[
			public function Test():String
			{
				return txtModule.text;
			}
		]]>
	</fx:Script>
	<s:TextArea right="0" left="0" top="0" bottom="0" contentBackgroundColor="#C8BBBB" text="this is a textarea in module" id="txtModule"/>
</mx:Module>

<?xml version="1.0" encoding="utf-8"?>
<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" minWidth="400" minHeight="300" applicationComplete="application1_applicationCompleteHandler(event)">
	<s:layout>
		<s:BasicLayout/>
	</s:layout>
	
	<fx:Script>
		<![CDATA[
			import mx.core.IVisualElement;
			import mx.events.FlexEvent;
			import mx.events.ModuleEvent;
			import mx.modules.IModuleInfo;
			import mx.modules.ModuleManager;
			
			private var module:IModuleInfo;
			private var first:Boolean=true;//是否首次加载的判断标志
			private var moduleInstance:Object;//用于保存加载后的实例引用

			protected function button1_clickHandler(event:MouseEvent):void
			{	
				//非首次加载（先卸载）
				if (!first)
				{
					module.unload();
					pnl.removeElement(moduleInstance as IVisualElement);
				}
				initModule();
				module.load();	
				btn1.enabled = false;
			}
			
			private function onModuleReady(e:ModuleEvent):void
			{				
				moduleInstance  = e.module.factory.create();//注：这里千万不能用as做任何的转型，否则就报null object reference错误，原因不明				
				this.pnl.addElement(moduleInstance as IVisualElement);
				//由于只能以Object方式操作，所以下面的代码，没办法智提示，只以盲打
				moduleInstance.txtModule.text = Math.random().toString();
				moduleInstance.x = moduleInstance.y = 10;
				trace(moduleInstance.Test());
				first = false;
				btn1.enabled = true;
				
			}
			
			private function initModule():void
			{
				module = ModuleManager.getModule("MyModule.swf");
				module.addEventListener(ModuleEvent.READY,onModuleReady);	
			}

			//应用加载完成时，就预先将Module初始化（甚至这时就可以load，只是不显示而已，以改善用户体验）
			protected function application1_applicationCompleteHandler(event:FlexEvent):void
			{
				initModule();
			}

		]]>
	</fx:Script>	
	
	<s:Panel id="pnl" title="动态加载Module" left="10" top="10" bottom="50" right="10"></s:Panel>
	
	<s:Button click="button1_clickHandler(event)" label="load" horizontalCenter="0" bottom="10" id="btn1">
		
	</s:Button>
</s:Application>