AutoFac的工作原理就是：注册类并映射到接口，通过注入后返回相应实例化的类！

     先来简单介绍下Autofac的使用

     1、通过Nuget或代码安装autofac

  

     安装autofac :install-package autofac

 

     安装对mvc4的支持：install -package autofac.mvc4

     2、新建相应的类及接口，并在autofac中进行映射

     2.1、新建接口 INewsHelper

namespace test.Interface 2 { 3     public interface INewsHelper 4  { 5         string GetNewInfo(int id); 6  } 7 }

      2.2、新建类NewsHelper并继承INewsHelper

namespace test.Helper  2 {  3     public class NewsHelper:INewsHelper  4  {  5         public string GetNewInfo(int id)  6  {  7             return "newshelper";  8  }  9  } 10 }

     2.3 新建类SubjectHelper并继承INewsHelper

namespace test.Helper  2 {  3     public class SubjectHelper:INewsHelper  4  {  5         public string GetNewInfo(int id)  6  {  7             return "subjecthelper";  8  }  9  
 } 11 }　　

     2.4 在autofac中注册并映射

namespace test  2 {  3     // 注意: 有关启用 IIS6 或 IIS7 经典模式的说明，  4     // 请访问 http://go.microsoft.com/?LinkId=9394801
 
    public class MvcApplication : System.Web.HttpApplication  7  {  8         protected void Application_Start()  9  { 10             var builder = new ContainerBuilder(); 11             builder.RegisterType<CategoryHelper>().As<ICategoryHelper>().InstancePerHttpRequest(); 12  
            builder.RegisterType<NewsHelper>().Named<INewsHelper>("news"); 14             builder.RegisterType<SubjectHelper>().Named<INewsHelper>("subject"); 15  
 builder.RegisterControllers(Assembly.GetExecutingAssembly()); 17             var container = builder.Build(); 18             DependencyResolver.SetResolver(new AutofacDependencyResolver(container)); 19  
 
 AreaRegistration.RegisterAllAreas(); 22  WebApiConfig.Register(GlobalConfiguration.Configuration); 23  FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); 24  RouteConfig.RegisterRoutes(RouteTable.Routes); 25  BundleConfig.RegisterBundles(BundleTable.Bundles); 26  AuthConfig.RegisterAuth(); 27  } 28  } 29 }　

     3、新建ServiceGetter类及  IServiceGetter接口

     3.1

namespace test.Interface 2 { 3     public interface IServiceGetter 4  { 5          T GetByName<T>(string name); 6  } 7 }　　

     3.2

namespace test.Helper  2 {  3     public class ServiceGetter:IServiceGetter  4  {  5         public T GetByName<T>(string name)  6  {  7             return AutofacDependencyResolver.Current.RequestLifetimeScope.ResolveNamed<T>(name);  8  }  9  } 10 }

     3.3 增加注册

      builder.RegisterType<ServiceGetter>().As<IServiceGetter>();

      整个步骤3做了一件事，给中间件一个泛型的name,由中间件向autofac将相应的class的实例并返回，说白了就是干了下面这句代码的事：

     AutofacDependencyResolver.Current.RequestLifetimeScope.ResolveNamed<INewsHelper>("news");

      4、通过构造函数进行注入

namespace test.Controllers  2 {  3     public class HomeController : Controller  4  {  5          
        private IServiceGetter getter;  7  
        public HomeController(IServiceGetter getter)  9  { 10              
            this.getter = getter; 12  
 } 14  
        public ActionResult Index() 16  { 17              
            ViewBag.Message = getter.GetByName<INewsHelper>