NopCommerce源码架构详解--Autofac依赖注入分析

NopCommerce整个代码里面都贯彻了一个面向接口编程的思想。nopCommerce商城系统是通过Autofac对接口依赖的实现进行依赖注入的。今天我们就来分析一下里面的源码，学习一下Nop在依赖注入方面设计思想，希望在以后的架构设计中对你有启发和帮助。

下面是Nop依赖注入相关类图。

可以看到这里面相关的类为

mvcApplication

IEngine，NopEngine

EngineContext

IDependencyRegistrar，DependencyRegistrar

下面我们再来看看这些类的核心代码。

我们打开Nop.Web项目的所有的Controller源码，可以看到基本上都是通过构造函数引用抽象的接口。如CustomerController的构造函数的参数类型都是某一个接口，如下图：

那我们要想看这些接口到底依赖的是哪一个真正的实现类呢？

在项目Nop.Web.Framework中有一个类DependencyRegistrar，其作用就是调用Autofac相关的API进行依赖注入，我们只要打开这个类文件，搜索一个指定的接口，就可以找到它依赖的具体类。例如，我们想看到ICategoryService接口是依赖哪一个实现，在这个类中搜索ICategoryService，会找到下面的代码：

1. builder.RegisterType<CategoryService>().As<ICategoryService>().InstancePerLifetimeScope();

可以看到这个接口对应的实现为为CategoryService（Nop.Services.Catalog命名空间下的类CategoryService）。

下面我们来看看Nop在网站启动是怎么调用这个DependencyRegistrar类呢？

在项目Nop.Web也就是前台的起始项目有一个文件Global.asax里有一个函数Application_Start，这函数的意义这里就不用说了，我相信学过ASP.NET同学都知道它的作用，下面是函数Application_Start的完整代码：

1. protected void Application_Start()
2. {
3. //初始化上下文引擎
4. EngineContext.Initialize(false);
6. //model binders
7. ModelBinders.Binders.Add(typeof(BaseNopModel), new NopModelBinder());
9. bool databaseInstalled = DataSettingsHelper.DatabaseIsInstalled();
10. if (databaseInstalled)
11. {
12. //remove all view engines
13. ViewEngines.Engines.Clear();
14. //except the themeable razor view engine we use
15. ViewEngines.Engines.Add(new ThemeableRazorViewEngine());
16. }
18. //Add some functionality on top of the default ModelMetadataProvider
19. ModelMetadataProviders.Current = new NopMetadataProvider();
21. //Registering some regular mvc stuff
22. AreaRegistration.RegisterAllAreas();
23. RegisterRoutes(RouteTable.Routes);
25. //fluent validation
26. DataAnnotationsModelValidatorProvider.AddImplicitRequiredAttributeForValueTypes = false;
27. ModelValidatorProviders.Providers.Add(new FluentValidationModelValidatorProvider(new NopValidatorFactory()));
29. //start scheduled tasks
30. if (databaseInstalled)
31. {
32. TaskManager.Instance.Initialize();
33. TaskManager.Instance.Start();
34. }
36. //log application start
37. if (databaseInstalled)
38. {
39. try
40. {
41. //log
42. var logger = EngineContext.Current.Resolve<ILogger>();
43. logger.Information("Application started", null, null);
44. }
45. catch (Exception)
46. {
47. //don't throw new exception if occurs
48. }
49. }
50. }

里面有第一行代码就调用了上下文引擎初始化。

1. EngineContext.Initialize(false);

下面我们来看看这个EngineContext的静态方法Initialize：

1. [MethodImpl(MethodImplOptions.Synchronized)]
2. public static IEngine Initialize(bool forceRecreate)
3. {
4. if (Singleton<IEngine>.Instance == null || forceRecreate)
5. {
6. var config = ConfigurationManager.GetSection("NopConfig") as NopConfig;
7. Singleton<IEngine>.Instance = CreateEngineInstance(config);
8. Singleton<IEngine>.Instance.Initialize(config);
9. }
10. return Singleton<IEngine>.Instance;
11. }

1. protected static IEngine CreateEngineInstance(NopConfig config)
2. {
3. if (config != null && !string.IsNullOrEmpty(config.EngineType))
4. {
5. var engineType = Type.GetType(config.EngineType);
6. if (engineType == null)
7. throw new ConfigurationErrorsException("The type '" + config.EngineType + "' could not be found. Please check the configuration at /configuration/nop/engine[@engineType] or check for missing assemblies.");
8. if (!typeof(IEngine).IsAssignableFrom(engineType))
9. throw new ConfigurationErrorsException("The type '" + engineType + "' doesn't implement 'Nop.Core.Infrastructure.IEngine' and cannot be configured in /configuration/nop/engine[@engineType] for that purpose.");
10. return Activator.CreateInstance(engineType) as IEngine;
11. }
13. return new NopEngine();
14. }

从上面可以看到Initialize返回一个IEngine的实例，并调用其方法Initialize。创建IEngine的实例是根据配置文件来获取哪一个IEngine的具体类，如果没有配置这个结点信息或者为空，则返回默认的IEngine的实现NopEngine。

下面我们来看看Nop.Core.Infrastructure.NopEngine里面的核心代码：

1. public void Initialize(NopConfig config)
2. {
3. //注册依赖
4. RegisterDependencies(config);
6. //startup tasks
7. if (!config.IgnoreStartupTasks)
8. {
9. RunStartupTasks();
10. }
12. }
14. /// <summary>
15. /// 注册依赖
16. /// </summary>
17. /// <param name="config">Config</param>
18. protected virtual void RegisterDependencies(NopConfig config)
19. {
20. var builder = new ContainerBuilder();
21. var container = builder.Build();
23. //we create new instance of ContainerBuilder
24. //because Build() or Update() method can only be called once on a ContainerBuilder.
27. //dependencies
28. var typeFinder = new WebAppTypeFinder(config);
29. builder = new ContainerBuilder();
30. builder.RegisterInstance(config).As<NopConfig>().SingleInstance();
31. builder.RegisterInstance(this).As<IEngine>().SingleInstance();
32. builder.RegisterInstance(typeFinder).As<ITypeFinder>().SingleInstance();
33. builder.Update(container);
35. //register dependencies provided by other assemblies
36. builder = new ContainerBuilder();
37. //查找所有实现了接口IDependencyRegistrar的类
38. var drTypes = typeFinder.FindClassesOfType<IDependencyRegistrar>();
39. var drInstances = new List<IDependencyRegistrar>();
40. foreach (var drType in drTypes)
41. drInstances.Add((IDependencyRegistrar) Activator.CreateInstance(drType));
42. //排序
43. drInstances = drInstances.AsQueryable().OrderBy(t => t.Order).ToList();
44.      //依次调用实现IDependencyRegistrar接口的类的方法Register
45. foreach (var dependencyRegistrar in drInstances)
46. dependencyRegistrar.Register(builder, typeFinder);
47. builder.Update(container);
50. this._containerManager = new ContainerManager(container);
52. //set dependency resolver
53. DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
54. }