Flex 带验证码的登陆页面

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns="*"     layout="vertical" creationComplete="initApp()">
<mx:states>
     <!--新建“index”State-->
   <mx:State name="index">
      <!--移除“登录框”-->
    <mx:RemoveChild target="{panel1}"/>
    <!--添加新的组件-->
    <mx:AddChild position="lastChild">
     <mx:Label x="231" y="174" text="欢迎来到主页" fontFamily="Georgia" fontSize="20" />
    </mx:AddChild>
   </mx:State>
</mx:states>
<mx:Script>
   <![CDATA[
   import mx.controls.Alert;
   private function initApp():void{
   lblCheckCode.text=GenerateCheckCode();
   }
   private function loginHandle():void{
     if(txtUsername.text=="" || txtPassword.text==""){
      Alert.show("用户名或者密码输入不完整！");
     }
     if(txtUsername.text=="licui"&& txtPassword.text=="123" && txtCheckCode.text.toLocaleLowerCase()==lblCheckCode.text.toLocaleLowerCase()){
      currentState="index";
     }else{
      if(txtCheckCode.text.toLocaleLowerCase()!=lblCheckCode.text.toLocaleLowerCase()){
       Alert.show("验证码不正确:");
       lblCheckCode.text=GenerateCheckCode();
      }else{
       Alert.show("用户名或者密码输入不正确!");
     }
    }
    }
   private function resetHandle():void{
     txtUs