本篇主要讲述MVC处理请求时创建Controller和执行Action的完整过程。
创建Controller
先查看MvcHandler中处理请求的方法BeginProcessRequest：
protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state) { IController controller; IControllerFactory factory; ProcessRequestInit(httpContext, out controller, out factory); IAsyncController asyncController = controller as IAsyncController; if (asyncController != null) { …… } else { …… } }
再查看其中创建Controller的方法ProcessRequestInit
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) { HttpContext currentContext = HttpContext.Current; …… AddVersionHeader(httpContext); RemoveOptionalRoutingParameters(); string controllerName = RequestContext.RouteData.GetRequiredString("controller"); factory = ControllerBuilder.GetControllerFactory(); controller = factory.CreateController(RequestContext, controllerName); …… }
Controller通过ControllerBuilder属性的方法GetControllerFactory获取到ControllerFactory对象然后由ControllerFactory创建，ControllerBuilder属性定义如下。
internal ControllerBuilder ControllerBuilder { get { if (_controllerBuilder == null) { _controllerBuilder = ControllerBuilder.Current; } return _controllerBuilder; } set { _controllerBuilder = value; } }
可知ControllerBuilder默认使用ControllerBuilder.Current，查看ControllerBuilder类的代码：
public IControllerFactory GetControllerFactory() { return _serviceResolver.Current; } internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver) { _serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>( () => _factoryThunk(),new DefaultControllerFactory { ControllerBuilder = this }, "ControllerBuilder.GetControllerFactory"); }
可知默认返回的ControllerFactory为DefaultControllerFactory（当然我们也可以注册默认的自定义的ControllerFactory），这里我们可继续查看DefaultControllerFactory
internal DefaultControllerFactory(……) { …… _activatorResolver = activatorResolver ?? new SingleServiceResolver<IControllerActivator>( () => null, new DefaultControllerActivator(dependencyResolver), "DefaultControllerFactory constructor"); } } private IControllerActivator ControllerActivator { get { if (_controllerActivator != null) { return _controllerActivator; } _controllerActivator = _activatorResolver.Current; return _controllerActivator; } } public virtual IController CreateController(RequestContext requestContext, string controllerName) { …… Type controllerType = GetControllerType(requestContext, controllerName); IController controller = GetControllerInstance(requestContext, controllerType); return controller; } protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType) { …… return ControllerActivator.Create(requestContext, controllerType); }
可以看到最终Controller由DefaultControllerActivator来创建
public DefaultControllerActivator(IDependencyResolver resolver) { if (resolver == null) { _resolverThunk = () => DependencyResolver.Current; } else { _resolverThunk = () => resolver; } } public IController Create(RequestContext requestContext, Type controllerType) { try { return (IController)(_resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType)); } catch (Exception ex) { throw new InvalidOperationException( String.Format( CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, controllerType), ex); } }
到此为止Controller就被创建出来了，这里我们看到了DependencyResolver.Current，这是MVC的默认注入容器，如果设置了容器，Controller的创建就可以通过容器（GetService）来完成了，如果未实现DependencyResolver或DependencyResolver未注册该Controller则通过反射来创建（使用Activator.CreateInstance，必须存在无参构造函数）。
Controller注入
下面来看对框架的第一个扩展也是最基本的扩展：为框架提供Ioc容器并注册Controller。对于Ioc容器的起源和作用这里就不多讲了。目前Ioc的思想已经普遍地应用于各种开发实践当中了，特别是企业应用开发中，Spring已经是Java开发事实上的基础框架。Asp.net Mvc也深受影响，虽然框架本身没有提供Ioc容器的实现，但是提供了很方便的扩展方式，通过扩展我们不仅可以使用容器管理自定义的对象，甚至可以将对象注入到Mvc框架当中（简单的比如对Controller的注入）。因为Mvc框架默认首先通过容器来获取对象，然后才是框架提供的方式（一般是一种默认实现），在以后的分析中可以看到许多的源码都可以证实这一点。
下面我们通过添加Autofac来实现依赖注入。
首先通过nuget添加Autofac和Autofac.Mvc5的引用。
在App_Start目录下添加Autofac的初始化类如下：
public class AutofacConfig { public static IDependencyResolver GeResolver() { var builder = new ContainerBuilder(); Registers(builder); builder.RegisterControllers(Assembly.GetExecutingAssembly()); return new AutofacDependencyResolver(builder.Build()); } private static void Registers(ContainerBuilder builder) { } }
然后在Global.asax的Application_Start方法中添加代码如下：
DependencyResolver.SetResolver(AutofacConfig.GeResolver());
这样我们就完成了依赖注入（目前只是Controller的注入，当然以后可以AutofacConfig 的Registers方法中把我们需要注入的对象注入到Autofac容器中）。关于依赖注入需要注意的主要有两点：一个是ContainerBuilder的扩展方法RegisterControllers，其参数类型为params Assembly[]可以传入一个或多个Assembly然后注册这些Assembly里的Controller，这样我们就可以将Controller放到不同的工程里；另一个是DependencyResolver.SetResolver，这样会替换掉默认的DependencyResolver实现，我们正是通过这样把Autofac容器作为了Mvc的容器从而完成依赖注入。
下面通过一个简单的例子说明Ioc容器的应用。首先创建一个简单的接口及其实现的类
public interface IIocTest { string Say(); } public class IocTest: IIocTest { public string Say() { return "IocTest"; } }
然后再HomeController中添加一个该接口的字段，并创建一个构造函数用于注入（AutoFac默认只支持构造函数注入，但也可以开启属性注入）。
private IIocTest iocTestInsatnce; public HomeController(IIocTest iocTest) { iocTestInsatnce = iocTest; }
然后再一个Action中调用接口方法，然后通过ViewBag（或其它方法）将其传到页面并显示，页面显示有多种方法，这里直接加到标题中：
public ActionResult Index() { ViewBag.iocSays = iocTestInsatnce.Say(); return View(); }
@{ ViewBag.Title = "Home Page"+ ViewBag.iocSays; }
然后运行程序，查看相应页面的标题，验证注入是否成功。
执行Action
创建好Controller之后我们再来看Controller是如何执行请求的。
首先看ControllerBase，这是所有Controller的基类，查看它的处理方法BeginExecuteCore。
protected virtual IAsyncResult BeginExecuteCore(AsyncCallback callback, object state) { …… try { string actionName = GetActionName(RouteData); IActionInvoker invoker = ActionInvoker; IAsyncActionInvoker asyncInvoker = invoker as IAsyncActionInvoker; if (asyncInvoker != null) { BeginInvokeDelegate<ExecuteCoreState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, ExecuteCoreState innerState) { return innerState.AsyncInvoker.BeginInvokeAction(innerState.Controller.ControllerContext, innerState.ActionName, asyncCallback, asyncState); }; EndInvokeVoidDelegate<ExecuteCoreState> endDelegate = delegate(IAsyncResult asyncResult, ExecuteCoreState innerState) { if (!innerState.AsyncInvoker.EndInvokeAction(asyncResult)) { innerState.Controller.HandleUnknownAction(innerState.ActionName); } }; ExecuteCoreState executeState = new ExecuteCoreState() { Controller = this, AsyncInvoker = asyncInvoker, ActionName = actionName }; return AsyncResultWrapper.Begin(callback, state, beginDelegate, endDelegate, executeState, _executeCoreTag); } else { …… } } …… }
可以看到Action的执行通过ActionInvoker. BeginInvokeAction实现，ActionInvoker的获取方式如下：
protected virtual IActionInvoker CreateActionInvoker() { return Resolver.GetService<IAsyncActionInvoker>() ?? Resolver.GetService<IActionInvoker>() ?? new AsyncControllerActionInvoker(); }
这里也看到了Resolver即可以通过Ioc容器来提供IAsyncActionInvoker或IActionInvoker，如果未提供则使用默认的AsyncControllerActionInvoker，再查看默认的实现AsyncControllerActionInvoker的处理方法BeginInvokeAction。
public virtual IAsyncResult BeginInvokeAction(ControllerContext controllerContext, string actionName, AsyncCallback callback, object state) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } Contract.Assert(controllerContext.RouteData != null); if (String.IsNullOrEmpty(actionName) && !controllerContext.RouteData.HasDirectRouteMatch()) { throw Error.ParameterCannotBeNullOrEmpty("actionName"); } ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext); ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName); if (actionDescriptor != null) { FilterInfo filterInfo = GetFilters(controllerContext, actionDescriptor); Action continuation = null; BeginInvokeDelegate beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState) { try { AuthenticationContext authenticationContext = InvokeAuthenticationFilters(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor); if (authenticationContext.Result != null) { AuthenticationChallengeContext challengeContext = InvokeAuthenticationFiltersChallenge(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor, authenticationContext.Result); continuation = () => InvokeActionResult(controllerContext, challengeContext.Result ?? authenticationContext.Result); } else { AuthorizationContext authorizationContext = InvokeAuthorizationFilters(controllerContext, filterInfo.AuthorizationFilters, actionDescriptor); if (authorizationContext.Result != null) { AuthenticationChallengeContext challengeContext = InvokeAuthenticationFiltersChallenge(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor, authorizationContext.Result); continuation = () => InvokeActionResult(controllerContext, challengeContext.Result ?? authorizationContext.Result); } else { if (controllerContext.Controller.ValidateRequest) { ValidateRequest(controllerContext); } IDictionary<string, object> parameters = GetParameterValues(controllerContext, actionDescriptor); IAsyncResult asyncResult = BeginInvokeActionMethodWithFilters(controllerContext, filterInfo.ActionFilters, actionDescriptor, parameters, asyncCallback, asyncState); continuation = () => { ActionExecutedContext postActionContext = EndInvokeActionMethodWithFilters(asyncResult); AuthenticationChallengeContext challengeContext = InvokeAuthenticationFiltersChallenge(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor, postActionContext.Result); InvokeActionResultWithFilters(controllerContext, filterInfo.ResultFilters, challengeContext.Result ?? postActionContext.Result); }; return asyncResult; } } } catch (ThreadAbortException) { throw; } catch (Exception ex) { ExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex); if (!exceptionContext.ExceptionHandled) { throw; } continuation = () => InvokeActionResult(controllerContext, exceptionContext.Result); } return BeginInvokeAction_MakeSynchronousAsyncResult(asyncCallback, asyncState); }; EndInvokeDelegate<bool> endDelegate = delegate(IAsyncResult asyncResult) { try { continuation(); } catch (ThreadAbortException) { throw; } catch (Exception ex) { ExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex); if (!exceptionContext.ExceptionHandled) { throw; } InvokeActionResult(controllerContext, exceptionContext.Result); } return true; }; return AsyncResultWrapper.Begin(callback, state, beginDelegate, endDelegate, _invokeActionTag); } else { return BeginInvokeAction_ActionNotFound(callback, state); } }
这是一个非常重要的方法，也是我们后续分析的基础，它描述了我们主要的处理流程。此方法中关联了相当多的类，但是其主要处理流程是容易清晰明白的。大致是先获取ControllerDescriptor和ActionDescriptor，然后依次执行Action中的过滤器AuthenticationFilters、AuthorizationFilters来进行验证和授权检查，然后是页面安全检查、获取参数，然后执行ActionFilter和Action，整个过程中如果设置了Result会直接执行AuthenticationFilters的AuthenticationFiltersChallenge，然后执行ResultFilters对结果进行过滤，当然如果处理过程中抛出异常会调用ExceptionFilter进行处理。如果要理解处理的细节需要查看大量的源码，这里提供一点小小的参考ReflectedActionDescriptor、ReflectedControllerDescriptor为ActionDescriptor和ControllerDescriptor的默认实现，Action、过滤器等的查找实际都是通过反射类获取的。
下面为BeginInvokeAction的处理过程图
