单例模式特点：
①控制某个类型的实例数量在整个应用程序中为唯一一个。
② 为客户程序提供一个获取该实例的全局访问点。
经典模式写法：
public class Singleton { private static Singleton instance; private Singleton() { } public static Singleton GetInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
多线程下的单例模式写法：
public class Singleton { private static Singleton instance; private static object _lock = new object(); private Singleton() { } public static Singleton GetInstance() { if (instance == null) { lock (_lock) { if (instance == null) { instance = new Singleton(); } } } return instance; } }
懒人模式写法：
public class Singleton { private static readonly Singleton instance = new Singleton(); private Singleton() { } public static Singleton GetInstance() { return instance; } }
原文：http://www.cnblogs.com/zqhxl/p/4932306.html
