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" layout="vertical" creationComplete="initApp()">
 <mx:states>
  <mx:State name="index">
   <mx:RemoveChild target="{loginPanel}"/>
   <mx:AddChild position="lastChild">
   <mx:Label 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=="admin" && txtPassword.text=="admin" && 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();
      txtCheckCode.text="";
     }else{
      Alert.show("用户名或密码输入不正确！");
     }
    }
   }
   
   private function resetHandle():void{
    txtUsername.text="";
    txtPassword.text="";
&nb