.NET：Microsoft.Practices.ServiceLocation 之 动态单例模式

背景

框架开发中，经常会用到“单例模式”，但是传统的单例模式不支持多态和运行时变化，在关注测试的今天，这种模式是不可行的。为了应对这种情况，微软又提供了另外一种模式，暂且将其称为“动态单例模式”。 我也想统一我的框架对单例的使用模式，因此就写了这篇文章。

Microsoft.Practices.ServiceLocation 核心代码

看完代码，如何使用这种模式就不用我多介绍了。

IServiceLocator

View Code

 1 using System;

 2 using System.Collections.Generic;

 3 

 4 namespace Microsoft.Practices.ServiceLocation

 5 {

 6     /// <summary>

 7     /// The generic Service Locator interface. This interface is used

 8     /// to retrieve services (instances identified by type and optional

 9     /// name) from a container.

10     /// </summary>

11     public interface IServiceLocator : IServiceProvider

12     {

13         /// <summary>

14         /// Get an instance of the given <paramref name="serviceType"/>.

15         /// </summary>

16         /// <param name="serviceType">Type of object requested.</param>

17         /// <exception cref="ActivationException">if there is an error resolving

18         /// the service instance.</exception>

19         /// <returns>The requested service instance.</returns>

20         object GetInstance(Type serviceType);

21 

22         /// <summary>

23         /// Get an instance of the given named <paramref name="serviceType"/>.

24         /// </summary>

25         /// <param name="serviceType">Type of object requested.</param>

26         /// <param name="key">Name the object was registered with.</param>

27         /// <exception cref="ActivationException">if there is an error resolving

28         /// the service instance.</exception>

29         /// <returns>The requested service instance.</returns>

30         object GetInstance(Type serviceType, string key);

31 

32         /// <summary>

33         /// Get all instances of the given <paramref name="serviceType"/> currently

34         /// registered in the container.

35         /// </summary>

36         /// <param name="serviceType">Type of object requested.</param>

37         /// <exception cref="ActivationException">if there is are errors resolving

38         /// the service instance.</exception>

39         /// <returns>A sequence of instances of the requested <paramref name="serviceType"/>.</returns>

40         IEnumerable<object> GetAllInstances(Type serviceType);

41 

42         /// <summary>

43         /// Get an instance of the given <typeparamref name="TService"/>.

44         /// </summary>

45         /// <typeparam name="TService">Type of object requested.</typeparam>

46         /// <exception cref="ActivationException">if there is are errors resolving

47         /// the service instance.</exception>

48         /// <returns>The requested service instance.</returns>

49         TService GetInstance<TService>();

50 

51         /// <summary>

52         /// Get an instance of the given named <typeparamref name="TService"/>.

53         /// </summary>

54         /// <typeparam name="TService">Type of object requested.</typeparam>

55         /// <param name="key">Name the object was registered with.</param>

56         /// <exception cref="ActivationException">if there is are errors resolving

57         /// the service instance.</exception>

58         /// <returns>The requested service instance.</returns>

59         TService GetInstance<TService>(string key);

60 

61         /// <summary>

62         /// Get all instances of the given <typeparamref name="TService"/> currently

63         /// registered in the container.

64         /// </summary>

65         /// <typeparam name="TService">Type of object requested.</typeparam>

66         /// <exception cref="ActivationException">if there is are errors resolving

67         /// the service instance.</exception>

68         /// <returns>A sequence of instances of the requested <typeparamref name="TService"/>.</returns>

69         IEnumerable<TService> GetAllInstances<TService>();

70     }

71 }

ServiceLocatorProvider

View Code

 1 namespace Microsoft.Practices.ServiceLocation

 2 {

 3     /// <summary>

 4     /// This delegate type is used to provide a method that will

 5     /// return the current container. Used with the <see cref="ServiceLocator"/>

 6     /// static accessor class.

 7     /// </summary>

 8     /// <returns>An <see cref="IServiceLocator"/>.</returns>

 9     public delegate IServiceLocator ServiceLocatorProvider();

10 }

ServiceLocator

View Code

 1 namespace Microsoft.Practices.ServiceLocation

 2 {

 3     /// <summary>

 4     /// This class provides the ambient container for this application. If your

 5     /// framework defines such an ambient container, use ServiceLocator.Current

 6     /// to get it.

 7     /// </summary>

 8     public static class ServiceLocator

 9     {

10         private static ServiceLocatorProvider currentProvider;

11 

12         /// <summary>

13         /// The current ambient container.

14         /// </summary>

15         public static IServiceLocator Current

16         {

17             get { return currentProvider(); }

18         }

19 

20         /// <summary>

21         /// Set the delegate that is used to retrieve the current container.

22         /// </summary>

23         /// <param name="newProvider">Delegate that, when called, will return

24         /// the current ambient container.</param>

25         public static void SetLocatorProvider(ServiceLocatorProvider newProvider)

26         {

27             currentProvider = newProvider;

28         }

29     }

30 }

动态单例模式的优点

1. 支持多态。
2. 运行时可变。
3. 支持其它级别范围的单例，如：请求级、线程级和会话级等。
4. 支持对象池。

备注

Microsoft.Practices.ServiceLocation下载地址：http://commonservicelocator.codeplex.com/。