这里我们把初始化工作放到Nested类中的一个静态成员来完成，这样就实现了延迟初始化。
Lazy<T> type
/// <summary>
/// .NET 4's Lazy<T> type
/// </summary>
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy =
new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton()
{
}
}
这种方式的简单和性能良好，而且还提供检查是否已经创建实例的属性IsValueCreated。
具体例子
现在让我们使用单例模式（Singleton）实现负载平衡器，首先我们定义一个服务器类，它包含服务器名和IP地址如下：
/// <summary>
/// Represents a server machine
/// </summary>
class Server
{
// Gets or sets server name
public string Name { get; set; }
// Gets or sets server IP address
public string IP { get; set; }
}
由于负载平衡器只提供一个对象实例供服务器使用，所以我们使用单例模式（Singleton）实现该负载平衡器。
/// <summary>
/// The 'Singleton' class
/// </summary>
sealed class LoadBalancer
{
private static readonly LoadBalancer _instance =
new LoadBalancer();
// Type-safe generic list of servers
private List<Server> _servers;
private Random _random = new Random();
static LoadBalancer()
{
}
// Note: constructor is 'private'
private LoadBalancer()
{
// Load list of available servers
_servers = new List<Server>
{
new Server{ Name = "ServerI", IP = "192.168.0.108" },
new Server{ Name = "ServerII", IP = "192.168.0.109" },
new Server{ Name = "ServerIII", IP = "192.168.0.110" },
new Server{ Name = "ServerIV", IP = "192.168.0.111" },
new Server{ Name = "ServerV", IP = "192.168.0.112" },
};
}
/// <summary>
/// Gets the instance through static initialization.
/// </summary>
public static LoadBalancer Instance
{
get { return _instance; }
}
// Simple, but effective load balancer
public Server NextServer
{
get
{
int r = _random.Next(_servers.Count);
return _servers[r];
}
}
}
上面负载平衡器类LoadBalancer我们使用静态初始化方式实现单例模式（Singleton）。
static void Main()
{
LoadBalancer b1 = LoadBalancer.Instance;
b1.GetHashCode();
LoadBalancer b2 = LoadBalancer.Instance;
LoadBalancer b3 = LoadBalancer.Instance;
LoadBalancer b4 = LoadBalancer.Instance;
// Confirm these are the same instance
if (b1 == b2 && b2 == b3 && b3 == b4)
{
Console.WriteLine("Same instancen");
}
// Next, load balance 15 requests for a server
LoadBalancer balancer = LoadBalancer.Instance;
for (int i = 0; i < 15; i++)
{
string serverName = balancer.NextServer.Name;
Console.WriteLine("Dispatch request to: " + serverName);
}
Console.ReadKey();
}
