普通模式：判断是否为空，如果没有instance，就new 一个；

 1 public class Singleton
 2 {
 3     private static Singleton instance;
 4     private Singleton()
 5     {
 6     }
 7     public Singleton GetInstance()
 8     {
 9         if(instance == null)
10         {
11             instance = new Singleton();
12         }
13         return instance;
14     }            
15 }

 

懒汉模式：直接在编译时new一个实例；也可以解决多线程的问题；

 1 public class Singleton
 2 {
 3     private static readonly Singleton instance = new Singleton();
 4     private Singleton()
 5     {
 6     }
 7     public Singleton GetInstance()
 8     {
 9         return instance;
10     }            
11 }