创建联动下拉列表.

原理很简单，改变数据源
示例：

代码：
 

<? xml version="1.0" encoding="utf-8" ?>
< mx:Application  xmlns:mx ="http://www.adobe.com/2006/mxml"  layout ="vertical"  verticalAlign ="middle"  backgroundColor ="white" >

     < mx:XML  id ="dp"  source ="countries_states.xml"  format ="e4x"   />

     < mx:Form >
         < mx:FormItem  label ="Country:" >
             < mx:ComboBox  id ="countryCB"  dataProvider =" {dp.country} "  labelField ="@name"   />
         </ mx:FormItem >
         < mx:FormItem  label ="State:" >
             < mx:ComboBox  id ="stateCB"  dataProvider =" {countryCB.selectedItem.state} "   />
         </ mx:FormItem >
     </ mx:Form >

</ mx:Application >