flex中的单例模式

actionscript3不能用private修饰构造方法，因此可以用一个内部类来做构造方法的参数：

 

package DesignPatterns
{
    import mx.controls.Alert;
    public class Singleton
    {
        private static var singleton:Singleton;
        public function Singleton(privateclass:privateClass)
        {
            Alert.show("this is pulic Class");
        }
        
        public static  function getInstance():Singleton{
            if(singleton==null){
                singleton = new Singleton(new privateClass());
            }
            return singleton;
        }
        
    }     
}

import mx.controls.Alert;
class privateClass{
        public function privateClass(){
            Alert.show("this is private Class");
        }
}