FLEX4 URLLoader与后台交互请求XML文件

<?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" 
			   xmlns:amcharts="http://www.amcharts.com/com_internal"
			   backgroundColor="#FFFFFF"
			   width="100%" height="100%"
			   initialize="initializeHandler(event)">
	
	<fx:Script>       

		private var _myService:URLLoader;
		
		private function initializeHandler(event:Event):void {
			_myService = new URLLoader(  );
			_myService.addEventListener(Event.COMPLETE,myCompleteHandler);
			_myService.load(new URLRequest("fileName.xml"));
			XML.ignoreWhitespace = true;
		}
		
		private function myCompleteHandler(event:Event):void {
			var xml:XML = new XML(_myService.data);
			myComboBox.dataProvider = xml.children(  );
		}		
		
	</fx:Script>
	
	<mx:VBox>
		<mx:ComboBox id="myComboBox" />
	</mx:VBox>
	
</s:Application>