Load swf and get a SimpleButton in it

Question

I load a swf and want to get a button in the swf. But the button I get is NULL. I am sure the button's name is right and exists. Could somebody help me to solve this problem?
package
import flash.display.MovieClip;
import flash.net.URLRequest;
import flash.display.Loader;
import flash.events.Event;
import flash.events.ProgressEvent;
import flash.display.SimpleButton;
import flash.display.LoaderInfo;
public class MyClass1 extends MovieClip
  public function MyClass1()
   super();
   var swfLoader:Loader = new Loader();
   addChild(swfLoader);
   var bgURL:URLRequest = new URLRequest("secondFlash.swf");
   swfLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadProdComplete);
   swfLoader.load(bgURL);
   var currentSWF:MovieClip = new MovieClip();
   function loadProdComplete(e:Event):void {
     var loaderInfo:LoaderInfo = e.target as LoaderInfo;
      var mv:MovieClip= MovieClip(loaderInfo.content);
    var btn1 = mv.getChildByName("btn1") as SimpleButton;
    trace("mv"+mv);
    trace("btn1="+btn1);

Answer 1

The code you show works fine for me.  How is btn1 created/named in the second swf file?  If you create it dynamically and do not assign a name property to it, it does not have the name you think it does.