How to see the .AS file that .MXML file is translated to before being compiled to SWF?

Question

I am trying to dynamically load some other Applications in
one Application, use ActionScript but not SWFLoader tag, it looks
like:
<mx:Application>
<mx:Script>
<![CDATA[
private var loader:SWFLoader = new SWFLoader();
private function loadSWF(url:String):void{
var baseURL:String = this.url.substr(0,
this.url.lastIndexOf("/"));
var url = baseURL + "/"+ name;
//even if I did not add any event listener!
loader.load(url);
]]>
</mx:Script>
<mx:Button label="B" click="loadSWF('Top_2.swf');" y="10"
x="58"/>
</mx:Application>
then when me click the button, always occured an error like
this:(even if every method I add try...catch... )
TypeError: Error #1009: Cannot access a property or method of
a null object reference.
at mx.core::UIComponent/
http://www.adobe.com/2006/flex/mx/internal::updateCallbacks()[E:\dev\3.0.x\frameworks\proj ects\framework\src\mx\core\UIComponent.as:5043
at mx.core::UIComponent/set
nestLevel()[E:\dev\3.0.x\frameworks\projects\framework\src\mx\core\UIComponent.as:2522]
at mx.managers::SystemManager/
http://www.adobe.com/2006/flex/mx/internal::addingChild()[E:\dev\3.0.x\frameworks\projects \framework\src\mx\managers\SystemManager.as:1583
at
mx.managers::SystemManager/initializeTopLevelWindow()[E:\dev\3.0.x\frameworks\projects\fr amework\src\mx\managers\SystemManager.as:2481]
at mx.managers::SystemManager/
http://www.adobe.com/2006/flex/mx/internal::docFrameHandler()[E:\dev\3.0.x\frameworks\proj ects\framework\src\mx\managers\SystemManager.as:2330
however, if I use <mx:SWFLoader source="Top_2.swf" />
tag, there is no such problem! So I think it must be I didn't init
SWFLoader correctly!
I hope someone can tell me how to crrect this mistake
directly, but I more wish someone to tell me how to view the .as
file that the .mxml file translated to before being compiled to a
SWF( If there is a such step!)
Thanks!

Answer 1

Maybe the SWFLoader must be one child of one DisplayObject!??
I found when the swfloader is been added to some
DisplayObject in actionScript like below, the problem didn't occure
any more.
swfloader.visible = false;
this.addChild(swfloader); // 'this' is current Application
swfloader.addEventListener(".....", someHandler);
swfloader.load("someurl");
Why? Is this a bug or not?
I am still waiting someone to tell me where a .mxml file can
be translated to a .as file which could be visited!