Flex与后台交互的4种方法

一、HTTPService
程序代码：
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="initializeHandler(event)">
<mx:Script>
<!--[CDATA[
private function initializeHandler(event:Event):void {
countriesService.send();
}
private function changeHandler(event:Event):void {
statesService.send();
}
]]>
</mx:Script>
<!-- 载入纯静态的xml数据 -->
<mx:HTTPService id="countriesService" url="http://www.rightactionscript.com/states/xml/countries.xml" />
<!-- 载入由php生成的xml数据 -->
<mx:HTTPService id="statesService" url="http://www.rightactionscript.com/states/xml/states.php">
<!-- 以下标签就是要发送到服务端的数据了,可以这样理解:有一个名为country的变量,它的值为花括号{}里的内容 -->
<mx:request>
<country>{country.value}</country>
</mx:request>
</mx:HTTPService>
<mx:VBox>
<!-- 此控件的数据由第一个<mx:HTTPService/>控件接收的内容提供,并且由这个ComboBox控制着第二个ComboBox所要显示的内容 -->
<mx:ComboBox id="country" dataProvider="{countriesService.lastResult.countries.country}"
change="changeHandler(event)" />
<!-- 下面的ComboBox已经绑定了{statesService.lastResult.states.state},随它的数据改变而改变 -->
<mx:ComboBox dataProvider="{statesService.lastResult.states.state}" />
</mx:VBox>
</mx:Application>  
二、URLLoader
程序代码：
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="initializeHandler(event)">
<mx:Script>
<!--[CDATA[
private var _countriesService:URLLoader;
private var _statesService:URLLoader;
private function initializeHandler(event:Event):void {
_countriesService = new URLLoader();
_countriesService.addEventListener(Event.COMPLETE, countriesCompleteHandler);
_countriesService.load(new URLRequest("http://www.rightactionsc