白话ASP.NET MVC之二：Controller激活系统的概览

前文简介：我们抽象类路由规则的对象，RouteBase是路由对象的抽象基类，ASP.NET 的路由系统中有唯一一个从RouteBase继承的路由对象，那就是Route类型了。我们注册了路由对象Route，UrlRoutingModule截获请求，把当前请求的Url地址和RouteTable路由表中注册的路由对象一个一个的比较，如果没有找到就返回Null，请求就到此终止了。如果有匹配的路由对象，选择第一个匹配的Route对象，并且根据该Route对象，生成了路由数据RouteData对象，本对象是为了封装成RequestContext对象，RequestContext对象封装了RouteData和HttpContext对象。

其实RequestContext对象也是作为参数使用的，我们根据Route对象获得了RouteData，该对象有一个RouteHandler属性，这个属性的值在ASP.NET MVC中是MvcRouteHandler。RouteHandler主要的作用是提供用于处理最终请求的HttpHandler对象，代码如下：

IHttpHandler=RouteData.RouteHandler.GetHttpHandler(requestContext);
HttpContext.Remap(IHttpHandler);

上文中我们获取到的RequestContext，将此作为参数调用RouteHandler的GetHttpHandler方法，我们获得了IHttpHandler对象，我们需要把请求交给这个HttpHandler来处理，通过HttpContext.Remap(Handler)实现请求的交接，这个Handler在ASP.NET MVC中就是MvcHandler，我们既然获得了HttpHandler对象，也实现了请求的交接，下一步该做什么呢？

一、概览

我们获得了用于处理请求HttpHandler对象，下一步最重要的任务是把Controller对象找到，RouteData对象的Values属性的Controller键和Action键的值只是一个字符串的结果，我们要通过这个名称找到具体的Controller类型实例，才能执行Action方法，给客户想要的应答。这篇文章就是Controller的激活方法的详解。

ASP.NET MVC系统真的很庞大，也很复杂，如果我们一上来就瀑布式的说，就像流水账一样，估计也不太容易说明白。为了便于理解，我们人为的把ASP.NET MVC这么庞大的系统拆分成相互独立，又有一定联系的多个子系统，然后我们各个击破，理解起来也就简单了，最后在把各个部分整合在一起，理解就全面了。今天我们要说的这一部分暂时叫做Controller激活系统吧，激活系统有两个含义，一是我们要找到我们需要的Controller对象，并实例化；二是我们药缓存他，并要执行它。

我们先来看看MvcHandler的源码吧，有助于我们的理解，代码如下：

         /// <summary>Selects the controller that will handle an HTTP request.</summary>
     public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
     {
         private struct ProcessRequestState
         {
             internal IAsyncController AsyncController;

             internal IControllerFactory Factory;

             internal RequestContext RequestContext;

             internal void ReleaseController()
             {
                 this.Factory.ReleaseController(this.AsyncController);
             }
         }

         private static readonly object _processRequestTag = new object();

         internal static readonly string MvcVersion = MvcHandler.GetMvcVersionString();

         /// <summary>Contains the header name of the ASP.NET MVC version.</summary>
         public static readonly string MvcVersionHeaderName = "X-AspNetMvc-Version";

         private ControllerBuilder _controllerBuilder;

         internal ControllerBuilder ControllerBuilder
         {
             get
             {
                 if (this._controllerBuilder == null)
                 {
                     this._controllerBuilder = ControllerBuilder.Current;
                 }
                 return this._controllerBuilder;
             }
             set
             {
                 this._controllerBuilder = value;
             }
         }

         /// <summary>Gets or sets a value that indicates whether the MVC response header is disabled.</summary>
         /// <returns>true if the MVC response header is disabled; otherwise, false.</returns>
         public static bool DisableMvcResponseHeader
         {
             get;
             set;
         }

         /// <summary>Gets a value that indicates whether another request can use the <see cref="T:System.Web.IHttpHandler" /> instance.</summary>
         /// <returns>true if the <see cref="T:System.Web.IHttpHandler" /> instance is reusable; otherwise, false.</returns>
         protected virtual bool IsReusable
         {
             get
             {
                 return false;
             }
         }

         /// <summary>Gets the request context.</summary>
         /// <returns>The request context.</returns>
         public RequestContext RequestContext
         {
             get;
             private set;
         }

         /// <summary>Gets a value that indicates whether another request can use the <see cref="T:System.Web.IHttpHandler" /> instance.</summary>
         /// <returns>true if the <see cref="T:System.Web.IHttpHandler" /> instance is reusable; otherwise, false.</returns>
         bool IHttpHandler.IsReusable
         {
             get
             {
                 return this.IsReusable;
             }
         }

         /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.MvcHandler" /> class.</summary>
         /// <param name="requestContext">The request context.</param>
         /// <exception cref="T:System.ArgumentNullException">The <paramref name="requestContext" /> parameter is null.</exception>
         public MvcHandler(RequestContext requestContext)
         {
             if (requestContext == null)
             {
                 throw new ArgumentNullException("requestContext");
             }
             this.RequestContext = requestContext;
         }

         /// <summary>Adds the version header by using the specified HTTP context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected internal virtual void AddVersionHeader(HttpContextBase httpContext)
         {
             if (!MvcHandler.DisableMvcResponseHeader)
             {
                 httpContext.Response.AppendHeader(MvcHandler.MvcVersionHeaderName, MvcHandler.MvcVersion);
             }
         }

         /// <summary>Called by ASP.NET to begin asynchronous request processing.</summary>
         /// <returns>The status of the asynchronous call.</returns>
         /// <param name="httpContext">The HTTP context.</param>
         /// <param name="callback">The asynchronous callback method.</param>
         /// <param name="state">The state of the asynchronous object.</param>
         protected virtual IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state)
         {
             HttpContextBase httpContext2 = new HttpContextWrapper(httpContext);
             return this.BeginProcessRequest(httpContext2, callback, state);
         }

         /// <summary>Called by ASP.NET to begin asynchronous request processing using the base HTTP context.</summary>
         /// <returns>The status of the asynchronous call.</returns>
         /// <param name="httpContext">The HTTP context.</param>
         /// <param name="callback">The asynchronous callback method.</param>
         /// <param name="state">The state of the asynchronous object.</param>
         protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state)
         {
             IController controller;
             IControllerFactory factory;
             this.ProcessRequestInit(httpContext, out controller, out factory);
             IAsyncController asyncController = controller as IAsyncController;
             if (asyncController != null)
             {
                 BeginInvokeDelegate<MvcHandler.ProcessRequestState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, MvcHandler.ProcessRequestState innerState)
                 {
                     IAsyncResult result;
                     try
                     {
                         result = innerState.AsyncController.BeginExecute(innerState.RequestContext, asyncCallback, asyncState);
                     }
                     catch
                     {
                         innerState.ReleaseController();
                         throw;
                     }
                     return result;
                 };
                 EndInvokeVoidDelegate<MvcHandler.ProcessRequestState> endDelegate = delegate(IAsyncResult asyncResult, MvcHandler.ProcessRequestState innerState)
                 {
                     try
                     {
                         innerState.AsyncController.EndExecute(asyncResult);
                     }
                     finally
                     {
                         innerState.ReleaseController();
                     }
                 };
                 MvcHandler.ProcessRequestState invokeState = new MvcHandler.ProcessRequestState
                 {
                     AsyncController = asyncController,
                     Factory = factory,
                     RequestContext = this.RequestContext
                 };
                 SynchronizationContext synchronizationContext = SynchronizationContextUtil.GetSynchronizationContext();
                 return AsyncResultWrapper.Begin<MvcHandler.ProcessRequestState>(callback, state, beginDelegate, endDelegate, invokeState, MvcHandler._processRequestTag, -, synchronizationContext);
             }
             Action action = delegate
             {
                 try
                 {
                     controller.Execute(this.RequestContext);
                 }
                 finally
                 {
                     factory.ReleaseController(controller);
                 }
             };
             return AsyncResultWrapper.BeginSynchronous(callback, state, action, MvcHandler._processRequestTag);
         }

         /// <summary>Called by ASP.NET when asynchronous request processing has ended.</summary>
         /// <param name="asyncResult">The asynchronous result.</param>
         protected internal virtual void EndProcessRequest(IAsyncResult asyncResult)
         {
             AsyncResultWrapper.End(asyncResult, MvcHandler._processRequestTag);
         }

         private static string GetMvcVersionString()
         {
             return new AssemblyName(typeof(MvcHandler).Assembly.FullName).Version.ToString();
         }

         /// <summary>Processes the request by using the specified HTTP request context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected virtual void ProcessRequest(HttpContext httpContext)
         {
             HttpContextBase httpContext2 = new HttpContextWrapper(httpContext);
             this.ProcessRequest(httpContext2);
         }

         /// <summary>Processes the request by using the specified base HTTP request context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected internal virtual void ProcessRequest(HttpContextBase httpContext)
         {
             IController controller;
             IControllerFactory controllerFactory;
             this.ProcessRequestInit(httpContext, out controller, out controllerFactory);
             try
             {
                 controller.Execute(this.RequestContext);
             }
             finally
             {
                 controllerFactory.ReleaseController(controller);
             }
         }

         private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
         {
             HttpContext current = HttpContext.Current;
             if (current != null && ValidationUtility.IsValidationEnabled(current) == true)
             {
                 ValidationUtility.EnableDynamicValidation(current);
             }
             this.AddVersionHeader(httpContext);
             this.RemoveOptionalRoutingParameters();
             string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");
             factory = this.ControllerBuilder.GetControllerFactory();
             controller = factory.CreateController(this.RequestContext, requiredString);
             if (controller == null)
             {
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_FactoryReturnedNull, new object[]
                 {
                     factory.GetType(),
                     requiredString
                 }));
             }
         }

         private void RemoveOptionalRoutingParameters()
         {
             RouteValueDictionary values = this.RequestContext.RouteData.Values;
             values.RemoveFromDictionary((KeyValuePair<string, object> entry) => entry.Value == UrlParameter.Optional);
         }

         /// <summary>Enables processing of HTTP Web requests by a custom HTTP handler that implements the <see cref="T:System.Web.IHttpHandler" /> interface.</summary>
         /// <param name="httpContext">An <see cref="T:System.Web.HttpContext" /> object that provides references to the intrinsic server objects (for example, Request, Response, Session, and Server) that are used to service HTTP requests.</param>
         void IHttpHandler.ProcessRequest(HttpContext httpContext)
         {
             this.ProcessRequest(httpContext);
         }

         /// <summary>Called by ASP.NET to begin asynchronous request processing using the base HTTP context.</summary>
         /// <returns>The status of the asynchronous call.</returns>
         /// <param name="context">The HTTP context.</param>
         /// <param name="cb">The asynchronous callback method.</param>
         /// <param name="extraData">The data.</param>
         IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
         {
             return this.BeginProcessRequest(context, cb, extraData);
         }

         /// <summary>Called by ASP.NET when asynchronous request processing has ended.</summary>
         /// <param name="result">The asynchronous result.</param>
         void IHttpAsyncHandler.EndProcessRequest(IAsyncResult result)
         {
             this.EndProcessRequest(result);
         }
     }

MvcHandler里面这个两个方法定义了Controller激活系统实现的骨架：

         /// <summary>Processes the request by using the specified base HTTP request context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected internal virtual void ProcessRequest(HttpContextBase httpContext)
         {
             IController controller;
             IControllerFactory controllerFactory;
             this.ProcessRequestInit(httpContext, out controller, out controllerFactory);
             try
             {
                 controller.Execute(this.RequestContext);
             }
             finally
             {
                 controllerFactory.ReleaseController(controller);
             }
         }

         private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
         {
             HttpContext current = HttpContext.Current;
             if (current != null && ValidationUtility.IsValidationEnabled(current) == true)
             {
                 ValidationUtility.EnableDynamicValidation(current);
             }
             this.AddVersionHeader(httpContext);
             this.RemoveOptionalRoutingParameters();
             string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");
             factory = this.ControllerBuilder.GetControllerFactory();
             controller = factory.CreateController(this.RequestContext, requiredString);
             if (controller == null)
             {
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_FactoryReturnedNull, new object[]
                 {
                     factory.GetType(),
                     requiredString
                 }));
             }
         }

代码不是很难，大家一看就能看懂，下一节好好的介绍一些Controller激活系统中所涉及到的各个对象，具体的解析规则要到下一篇文章了，否则文章就太长了。

二、Controller对象激活详述

ASP.NET MVC中，我们人为分解的当前系统叫：Controller激活系统，其实这个激活系统里面包含的对象也不是很多，主要有我们要实例化的Controller对象，管理Controller的ControllerFactory对象，管理ControllerFactory的ControllerBuilder对象，这三个主要对象构成了我们的激活系统。

1、我们先看看Controller类型的定义吧

我们所说的Controller其实是指实现了IController接口的某个类型实例。Controller是一个可以执行的对象，它的执行体现在对Execute方法上的调用。一说到执行我们是不是就会想到同步执行和异步执行呢，既然Controller是一个可以执行的对象，他会不会也具有同步和异步的执行呢，答案是肯定的，我们先来看看两个接口吧：

public interface IController
{
    /// <summary>Executes the specified request context.</summary>
    /// <param name="requestContext">The request context.</param>
    void Execute(RequestContext requestContext);
}

这个就是同步版的接口，该接口的命名空间是：System.Web.Mvc，当目标Controller对象被成功激活后，对请求的后续处理和最终响应都通过执行者Execute方法来实现。我们再看看异步版的接口定义吧：

 public interface IAsyncController : IController
 {
     /// <summary>Executes the specified request context.</summary>
     /// <returns>The status of the asynchronous operation.</returns>
     /// <param name="requestContext">The request context.</param>
     /// <param name="callback">The asynchronous callback method.</param>
     /// <param name="state">The state.</param>
     IAsyncResult BeginExecute(RequestContext requestContext, AsyncCallback callback, object state);

     /// <summary>Ends the asynchronous operation.</summary>
     /// <param name="asyncResult">The asynchronous result.</param>
     void EndExecute(IAsyncResult asyncResult);
 }

异步版接口定义的命名空间是：System.Web.Mvc.Async，我们看到IAsyncController是实现了IController的接口，Controller的异步执行是通过调用BeginExecute和EndExecute方法来实现的。我们通过Visual Studio创建的ASP.NET MVC项目，我们自定义的Controller实现的基类是Controller类型，不是直接实现以上接口的。我们看看Controller类型的定义吧：

public abstract class Controller : ControllerBase, IActionFilter, IAuthenticationFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IController, IAsyncManagerContainer
{
//代码省略
}

Controller是抽象类型，实现了很多接口，因为该类的代码太多，所以省略了部分内部代码，这个里面牵扯到另外一个类，就是ControllerBase，

 /// <summary>Represents the base class for all MVC controllers.</summary>
 public abstract class ControllerBase : IController
 {
     private readonly SingleEntryGate _executeWasCalledGate = new SingleEntryGate();

     private DynamicViewDataDictionary _dynamicViewDataDictionary;

     private TempDataDictionary _tempDataDictionary;

     private bool _validateRequest = true;

     private IValueProvider _valueProvider;

     private ViewDataDictionary _viewDataDictionary;

     /// <summary>Gets or sets the controller context.</summary>
     /// <returns>The controller context.</returns>
     public ControllerContext ControllerContext
     {
         get;
         set;
     }

     /// <summary>Gets or sets the dictionary for temporary data.</summary>
     /// <returns>The dictionary for temporary data.</returns>
     public TempDataDictionary TempData
     {
         get
         {
             if (this.ControllerContext != null && this.ControllerContext.IsChildAction)
             {
                 return this.ControllerContext.ParentActionViewContext.TempData;
             }
             if (this._tempDataDictionary == null)
             {
                 this._tempDataDictionary = new TempDataDictionary();
             }
             return this._tempDataDictionary;
             }
         set
         {
             this._tempDataDictionary = value;
         }
     }

     /// <summary>Gets or sets a value that indicates whether request validation is enabled for this request.</summary>
     /// <returns>true if request validation is enabled for this request; otherwise, false. The default is true.</returns>
     public bool ValidateRequest
     {
         get
         {
             return this._validateRequest;
         }
         set
         {
             this._validateRequest = value;
         }
     }

     /// <summary>Gets or sets the value provider for the controller.</summary>
     /// <returns>The value provider for the controller.</returns>
     public IValueProvider ValueProvider
     {
         get
         {
             if (this._valueProvider == null)
             {
                 this._valueProvider = ValueProviderFactories.Factories.GetValueProvider(this.ControllerContext);
             }
             return this._valueProvider;
         }
         set
         {
             this._valueProvider = value;
         }
     }

     /// <summary>Gets the dynamic view data dictionary.</summary>
     /// <returns>The dynamic view data dictionary.</returns>
     [Dynamic]
     public dynamic ViewBag
     {
         [return: Dynamic]
         get
         {
             if (this._dynamicViewDataDictionary == null)
             {
                 this._dynamicViewDataDictionary = new DynamicViewDataDictionary(() => this.ViewData);
             }
             return this._dynamicViewDataDictionary;
         }
     }

     /// <summary>Gets or sets the dictionary for view data.</summary>
     /// <returns>The dictionary for the view data.</returns>
     public ViewDataDictionary ViewData
     {
         get
         {
             if (this._viewDataDictionary == null)
             {
                 this._viewDataDictionary = new ViewDtaDictionary();
             }
             return this._viewDataDictionary;
         }
         set
         {
             this._viewDataDictionary = value;
         }
     }
     /// <summary>Executes the specified request context.</summary>
     /// <param name="requestContext">The request context.</param>
     /// <exception cref="T:System.ArgumentNullException">The <paramref name="requestContext" /> parameter is null.</exception>
     protected virtual void Execute(RequestContext requestContext)
     {
         if (requestContext == null)
         {
             throw new ArgumentNullException("requestContext");
         }
         if (requestContext.HttpContext == null)
         {
             throw new ArgumentException(MvcResources.ControllerBase_CannotExecuteWithNullHttpContext, "requestContext");
         }
         this.VerifyExecuteCalledOnce();
         this.Initialize(requestContext);
         using (ScopeStorage.CreateTransientScope())
         {
             this.ExecuteCore();
         }
     }

     /// <summary>Executes the request.</summary>
     protected abstract void ExecuteCore();

     /// <summary>Initializes the specified request context.</summary>
     /// <param name="requestContext">The request context.</param>
     protected virtual void Initialize(RequestContext requestContext)
     {
         this.ControllerContext = new ControllerContext(requestContext, this);
     }

     internal void VerifyExecuteCalledOnce()
     {
         if (!this._executeWasCalledGate.TryEnter())
         {
             string message = string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBase_CannotHandleMultipleRequests, new object[]
             {
                 base.GetType()
             });
             throw new InvalidOperationException(message);
         }
     }

     /// <summary>Executes the specified request context.</summary>
     /// <param name="requestContext">The request context.</param>
     void IController.Execute(RequestContext requestContext)
     {
         this.Execute(requestContext);
     }
 }

ControllerBase实现了IController接口，但是没有实现IAsyncController接口，说明ControllerBase是一个同步的基类，之所以单独又增加ControllerBase，个人认为它定义了方法调用的扩展点。ControllerBase是一个抽象类，通过显示的实现了IController的Execute方法，在这个显示实现的方法IController.Execute方法里面又调用了受保护的虚方法Execute，这个受保护的虚方法Execute又在内部调用了抽象方法ExecuteCore，作为ControllerBase的继承者，必须通过实现对抽象方法ExecuteCore来完成对Controller的执行。这个过程就是方法调用的扩展点，而且ControllerBase也抽象所有Controller中都会用到的一些共同的属性，如TempData，ControllerContext，ValueProvider，ViewBag，ViewData等，大家可以细细研究，这里就不细说了，都很简单。

在ControllerBase里面有一个初始化的方法，这个方法的作用是根据当前Controller对象和当前请求上下文RequestContext创建ControllerContext对象，在请求后续处理的时候很多地方会用到ControllerContext。

/// <summary>Initializes the specified request context.</summary>
/// <param name="requestContext">The request context.</param>
protected virtual void Initialize(RequestContext requestContext)
{
    this.ControllerContext = new ControllerContext(requestContext, this);
}

此方法是虚方法，我们可以扩展他，这个方法的调用点在受保护的虚方法Exuecute中，在调用ExecuteCore之前调用了该方法。

我们说了接口IController，IAsyncController，也说了抽象类ControllerBase，我们最后对我们要经常使用的基类做一下简述，我们真正在项目中使用的Controller的基类型是Controller类型，Controller实现了IController接口和IAsyncController接口，说明我们自己的Controller是可以同步执行，也可以异步执行的，同时实现了IDisposable接口，说明Controller类型是需要释放的，谁来释放激活的Controller的类型呢，那就是我们接下来要说的一个对象ControllerFactory，这里不多说，下面会解释清楚的。

最后我们需要说明的，虽然Controller可以同步执行，也可以异步执行，但是是同步还是异步是靠DisableAsyncSupport属性控制的，返回的是布尔值，默认情况是false，意思是指支持异步执行，以下代码说明实际情况。当BeginExecute方法执行的时候，它会根据该属性的值决定调用Execute同步执行Controller，还是调用BeginExecuteCore/EndExecuteCore方法异步执行Controller，换句话说，如果总是希望Controller同步执行，那就要把DisableAsyncSupport属性设置为true。

 protected virtual IAsyncResult BeginExecute(RequestContext requestContext, AsyncCallback callback, object state)
 {
             if (this.DisableAsyncSupport)
             {
                 Action action = delegate
                 {
                     this.Execute(requestContext);
                 };
                 return AsyncResultWrapper.BeginSynchronous(callback, state, action, Controller._executeTag);
             }
             if (requestContext == null)
             {
                 throw new ArgumentNullException("requestContext");
             }
                          this.Initialize(requestContext);
             BeginInvokeDelegate<Controller> beginDelegate = (AsyncCallback asyncCallback, object callbackState, Controller controller) => controller.BeginExecuteCore(asyncCallback, callbackState);
             EndInvokeVoidDelegate<Controller> endDelegate = delegate(IAsyncResult asyncResult, Controller controller)
             {
                 controller.EndExecuteCore(asyncResult);
             };
             return AsyncResultWrapper.Begin<Controller>(callback, state, beginDelegate, endDelegate, this, Controller._executeTag, -, null);
 }

2、ControllerContext

在ASP.NET MVC中我们会遇到很多上下文（Context）的类型，比如：RequestContext，它是对HttpContext和RouteData的封装，今天我们看看ControllerContext，就是指Controller的上下文，再说明白一点就是Controller在执行过程中对需要用到的一些数据的封装对象，它类似一个Facade，里面包含了一些在Controller执行时所要用的一些对象，必须表示请求的HttpContextBase对象。这个类型没什么可说的，很简单，我把反编译的代码也都贴出来了，大家可以自己看。

 /// <summary>Encapsulates information about an HTTP request that matches specified <see cref="T:System.Web.Routing.RouteBase" /> and <see cref="T:System.Web.Mvc.ControllerBase" /> instances.</summary>
 public class ControllerContext
 {
     private sealed class EmptyHttpContext : HttpContextBase
     {
     }

     internal const string ParentActionViewContextToken = "ParentActionViewContext";

     private HttpContextBase _httpContext;

     private RequestContext _requestContext;

     private RouteData _routeData;

     /// <summary>Gets or sets the controller.</summary>
     /// <returns>The controller.</returns>
     public virtual ControllerBase Controller
     {
         get;
         set;
     }

     /// <summary>Gets the display mode.</summary>
     /// <returns>The display mode.</returns>
     public IDisplayMode DisplayMode
     {
         get
         {
             return DisplayModeProvider.GetDisplayMode(this.HttpContext);
         }
         set
         {
             DisplayModeProvider.SetDisplayMode(this.HttpContext, value);
         }
     }

     /// <summary>Gets or sets the HTTP context.</summary>
     /// <returns>The HTTP context.</returns>
     public virtual HttpContextBase HttpContext
     {
         get
         {
             if (this._httpContext == null)
             {
                 this._httpContext = ((this._requestContext != null) ? this._requestContext.HttpContext : new ControllerContext.EmptyHttpContext());
             }
             return this._httpContext;
         }
         set
         {
             this._httpContext = value;
         }
     }

     /// <summary>Gets a value that indicates whether the associated action method is a child action.</summary>
     /// <returns>true if the associated action method is a child action; otherwise, false.</returns>
     public virtual bool IsChildAction
     {
         get
         {
             RouteData routeData = this.RouteData;
             return routeData != null && routeData.DataTokens.ContainsKey("ParentActionViewContext");
         }
     }

     /// <summary>Gets an object that contains the view context information for the parent action method.</summary>
     /// <returns>An object that contains the view context information for the parent action method.</returns>
     public ViewContext ParentActionViewContext
     {
         get
         {
             return this.RouteData.DataTokens["ParentActionViewContext"] as ViewContext;
         }
     }

     /// <summary>Gets or sets the request context.</summary>
     /// <returns>The request context.</returns>
     public RequestContext RequestContext
     {
         get
         {
             if (this._requestContext == null)
             {
                 HttpContextBase httpContext = this.HttpContext ?? new ControllerContext.EmptyHttpContext();
                 RouteData routeData = this.RouteData ?? new RouteData();
                 this._requestContext = new RequestContext(httpContext, routeData);
             }
             return this._requestContext;
         }
         set
         {
             this._requestContext = value;
         }
     }

     /// <summary>Gets or sets the URL route data.</summary>
     /// <returns>The URL route data.</returns>
     public virtual RouteData RouteData
     {
         get
         {
             if (this._routeData == null)
             {
                 this._routeData = ((this._requestContext != null) ? this._requestContext.RouteData : new RouteData());
             }
             return this._routeData;
         }
         set
         {
             this._routeData = value;
         }
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.ControllerContext" /> class.</summary>
     public ControllerContext()
     {
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.ControllerContext" /> class by using the specified controller context.</summary>
     /// <param name="controllerContext">The controller context.</param>
     /// <exception cref="T:System.ArgumentNullException">The <paramref name="controllerContext" /> parameter is null.</exception>
     protected ControllerContext(ControllerContext controllerContext)
     {
         if (controllerContext == null)
         {
             throw new ArgumentNullException("controllerContext");
         }
         this.Controller = controllerContext.Controller;
         this.RequestContext = controllerContext.RequestContext;
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.ControllerContext" /> class by using the specified HTTP context, URL route data, and controller.</summary>
     /// <param name="httpContext">The HTTP context.</param>
     /// <param name="routeData">The route data.</param>
     /// <param name="controller">The controller.</param>
     public ControllerContext(HttpContextBase httpContext, RouteData routeData, ControllerBase controller) : this(new RequestContext(httpContext, routeData), controller)
     {
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.ControllerContext" /> class by using the specified request context and controller.</summary>
     /// <param name="requestContext">The request context.</param>
     /// <param name="controller">The controller.</param>
     /// <exception cref="T:System.ArgumentNullException">One or both parameters are null.</exception>
     public ControllerContext(RequestContext requestContext, ControllerBase controller)
     {
         if (requestContext == null)
         {
             throw new ArgumentNullException("requestContext");
         }
         if (controller == null)
         {
             throw new ArgumentNullException("controller");
         }
         this.RequestContext = requestContext;
         this.Controller = controller;
     }
 }

3、ControllerFactory

我们的Controller对象有了，为了解耦和可扩展性，ASP.NET MVC 框架中不可能直接new一个Controller的实例对象吧，我们在MvcHandler的代码中也看到了是基于接口编程的，所以需要提供一种机制，来提供我们要得到的Controller对象。既然不能直接new一个Controller出来，那我们就封装new的过程，用工厂来代替吧。对了，就是工厂，这个工厂就是ControllerFactory，从名字上可以看出它的意思，创建Controller对象的工厂。ASP.NET MVC是可以扩展的，可以自定义的，我们的ControllerFactory工厂也不例外，所以我们就产生了ControllerFactory工厂的接口，接口的名字是IControllerFactory，所有的ControllerFactory都必须实现该接口。接口定义如下：

       /// <summary>Defines the methods that are required for a controller factory.</summary>
     public interface IControllerFactory
     {
         /// <summary>Creates the specified controller by using the specified request context.</summary>
         /// <returns>The controller.</returns>
         /// <param name="requestContext">The request context.</param>
         /// <param name="controllerName">The name of the controller.</param>
         IController CreateController(RequestContext requestContext, string controllerName);

         /// <summary>Gets the controller's session behavior.</summary>
         /// <returns>The controller's session behavior.</returns>
         /// <param name="requestContext">The request context.</param>
         /// <param name="controllerName">The name of the controller whose session behavior you want to get.</param>
         SessionStateBehavior GetControllerSessionBehavior(RequestContext requestContext, string controllerName);

         /// <summary>Releases the specified controller.</summary>
         /// <param name="controller">The controller.</param>
         void ReleaseController(IController controller);
     }

IControllerFactory接口是对管理Controller对象的工厂的抽象，怎么管理呢，无非就是我要创建一个Controller就能创建一个Controller。我们创建好了Controller，不使用的情况就要能销毁它，能创建和能销毁就构成了IControllerFactory的主要功能，CreateController用于创建Controller对象实例，ReleaseController方法用于销毁不用的Controller对象，因为我们的Controller实现了IDisposable接口。想起来了吗？因为我们自定义的Controller都继承了抽象基类Controller类型，该抽象Controller基类实现了IDisposable接口。

IControllerFactory接口还有一个方法GetControllerSessionBehavior，用于管理Controller的会话状态，返回的类型为SessionStateBehavior枚举值，它有四个枚举值：Default（使用默认的ASP.NET逻辑来确定请求的会话行为），Required（为请求启用完全的读和写会话状态的行为），ReadOnly（为请求启用只读的会话状态），Disabled（禁用会话状态）。说起来话长，在System.Web.SessionState命名空间下有两个接口定义，分别是IRequiresSessionState（实现本接口，HttpHandler采用Required会话模式）和IReadOnlySessionState（实现本接口，HttpHandler采用ReadOnly会话模式）类型，这个两个接口是标记接口，没有定义具体的方法。我们在看看我们的MvcHandler类型的定义吧，代码如下：

public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState

具体采用何种会话状态行为取决于当前Http请求上下文（HttpContext的静态属性Current表示的对象），对于ASP.NET 3.0及其以前的版本，我们不能对当前的Http上下文的会话状态行为模式进行修改，在ASP.NET 4.0中为HttpContext对象定义了一个SetSessionStateBehavior方法，此方法也在HttpContextBase定义了，HttpContextBase的子类HttpContextWrapper重写了这个方法，在内部调用HttpContext的同名方法来设置当前请求的会话状态模式。

4、ControllerBuilder

我们有了Controller，可以通过IController，IAsyncController，ControllerBase或者Controller抽象基类来自定义我们自己的Controller基类型，我们也有了IControllerFactory接口，可以管理Controller对象，也可以定义我们自己的ControllerFactory来取代系统的默认实现。问题来了，我们自定义了ControllerFactory对象，但是如何把我们自定义的ControllerFactory放到ASP.NET MVC框架中呢，那就需要我们这个类型了，它的名字就是ControllerBuilder。

代码最有说服力，我们先上代码吧，源码如下：

      /// <summary>Represents a class that is responsible for dynamically building a controller.</summary>
     public class ControllerBuilder
     {
         private static ControllerBuilder _instance = new ControllerBuilder();

         private Func<IControllerFactory> _factoryThunk = () => null;

         private HashSet<string> _namespaces = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

         private IResolver<IControllerFactory> _serviceResolver;

         /// <summary>Gets the current controller builder object.</summary>
         /// <returns>The current controller builder.</returns>
         public static ControllerBuilder Current
         {
             get
             {
                 return ControllerBuilder._instance;
             }
         }

         /// <summary>Gets the default namespaces.</summary>
         /// <returns>The default namespaces.</returns>
         public HashSet<string> DefaultNamespaces
         {
             get
             {
                 return this._namespaces;
             }
         }

         /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.ControllerBuilder" /> class.</summary>
         public ControllerBuilder() : this(null)
         {
         }

         internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver)
         {
             IResolver<IControllerFactory> arg_6A_1 = serviceResolver;
             if (serviceResolver == null)
             {
                 arg_6A_1 = new SingleServiceResolver<IControllerFactory>(() => this._factoryThunk(), new DefaultControllerFactory
                 {
                     ControllerBuilder = this
                 }, "ControllerBuilder.GetControllerFactory");
             }
             this._serviceResolver = arg_6A_1;
         }

         /// <summary>Gets the associated controller factory.</summary>
         /// <returns>The controller factory.</returns>
         public IControllerFactory GetControllerFactory()
         {
             return this._serviceResolver.Current;
         }

         /// <summary>Sets the specified controller factory.</summary>
         /// <param name="controllerFactory">The controller factory.</param>
         /// <exception cref="T:System.ArgumentNullException">The <paramref name="controllerFactory" /> parameter is null.</exception>
         public void SetControllerFactory(IControllerFactory controllerFactory)
         {
             if (controllerFactory == null)
             {
                 throw new ArgumentNullException("controllerFactory");
             }
             this._factoryThunk = (() => controllerFactory);
         }

         /// <summary>Sets the controller factory by using the specified type.</summary>
         /// <param name="controllerFactoryType">The type of the controller factory.</param>
         /// <exception cref="T:System.ArgumentNullException">The <paramref name="controllerFactoryType" /> parameter is null.</exception>
         /// <exception cref="T:System.ArgumentException">The controller factory cannot be assigned from the type in the <paramref name="controllerFactoryType" /> parameter.</exception>
         /// <exception cref="T:System.InvalidOperationException">An error occurred while the controller factory was being set.</exception>
         public void SetControllerFactory(Type controllerFactoryType)
         {
             if (controllerFactoryType == null)
             {
                 throw new ArgumentNullException("controllerFactoryType");
             }
             if (!typeof(IControllerFactory).IsAssignableFrom(controllerFactoryType))
             {
                 throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_MissingIControllerFactory, new object[]
                 {
                     controllerFactoryType
                 }), "controllerFactoryType");
             }
             this._factoryThunk = delegate
             {
                 IControllerFactory result;
                 try
                 {
                     result = (IControllerFactory)Activator.CreateInstance(controllerFactoryType);
                 }
                 catch (Exception innerException)
                 {
                     throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_ErrorCreatingControllerFactory, new object[]
                     {
                         controllerFactoryType
                     }), innerException);
                 }
                 return result;
             };
         }
     }

源码不是很多，我贴出了完整的代码。

ControllerBuilder定义了一个静态只读属性Current，返回当前使用的ControllerBuilder对象。该类型有一个返回类型为IControllerFactory的方法GetControllerFactory，这个方法用于获取当前注册的ControllerFactory对象。ControllerBuilder类型还有两个重载的SetControllerFactory方法，这两个方法的主要作用是把我们自定义的ControllerFactory注册到ASP.NET MVC框架中去。但是这两个方法有些不同，参数类型为IControllerFactory的SetControllerFactory方法直接注册ControllerFactory实例对象，而参数类型为Type的SetControllerFactory方法注册的ControllerFactory的类型。

如果我们注册的是ControllerFactory类型的话，那么GetControllerFactory方法在获取ControllerFactory对象的时候都要通过反射来获得，也就是说针对GetControllerFactory方法的每次调用都会伴随着ControllerFactory的实例化，ASP.NET MVC框架不会对实例化的ControllerFactory进行缓存。如果我们注册的是ControllerFactory对象实例，针对GetControllerFactory方法来说是直接返回注册的对象，就性能而言，注册ControllerFactory对象比较好。

命名空间

       如果在多个命名空间下定义了多个同名的Controller类型，如果只是按着名称来匹配就会导致激活系统无法确定具体的Controller的类型而抛出异常。为了解决这个问题，我们必须为定义了同名的Controller类型的命名空间设置不同的优先级。

ASP.NET MVC的Controller的激活系统为我们提供了两种提升命名空间优先级的方法。第一种方法就是通过调用RouteCollectionExtensions的扩展方法MapRoute的时候提供命名空间列表。此种方式指定的命名空间列表会保存在Route路由对象的DataTokens属性中，对应的Key是Namespaces。第二种方式就是把命名空间列表添加到当前的ControllerBuilder类型的默认命名空间列表中。这些命名空间列表存放在返回类型为HashSet<string>的DefaultNamespaces属性中。这两种方法的优先级第一种方法更高。

对于Area的命名空间来说，如果我们在调用AreaRegistrationContext对象的MapRoute方法时提供了命名空间，该命名空间会作为Route对象的命名空间，如果没有提供，则AreaRegistration类型所在的命名空间，再加上“.*”作为Route对象的命名空间。当我们调用AreaRegistrationContext的MapRoute方法的时候，会在Route对象的DataTokens属性里增加一个Key为UseNamespaceFallback的变量，它表示是否采用后备的命名空间来解析Controller类型。如果Route对象有命名空间，该值就是False，否则就是true。

解析过程是，ASP.NET MVC会先使用RouteData包含的命名空间，如果解析失败，它会从RouteData对象的DataTokens属性中取出Key为UseNamespaceFallback的值，如果该值为true或者不存在，就使用ControllerBuidler的默认命名空列表来解析。如果UseNamespaceFallback的值为false，就不实用后备的命名空间，如果没找到就会抛出异常。

三、激活Controller类型的缓存和释放

一个比较大的系统里面，可能所涉及到的Controller类型成千上万，如果每次都要通过反射的方式及时获取，那对性能的影响是很客观的，ASP.NET MVC框架组想到了这一点，针对Controller和AreaRegistration都实现了彻底的缓存，这个缓存是把所有解析出来的类型持久化到物理文件中，两个物理文件的名称分别是：MVC-ControllerTypeCache.xml和MVC-AreaRegistrationTypeCache.xml，具体的目录在%windir%\Microsoft.Net\Framework\v{version}\Temporary ASP.NET Files\root\..\..\UserCache\。

当接收到web应用被启动后的第一个请求的时候，Controller激活系统会读取这些文件，通过反序列化生成List<Type>对象。

MVC-ControllerTypeCache.xml代码如下：

<?xml version="1.0" encoding="UTF-8"?>

<!--This file is automatically generated. Please do not modify the contents of this file.-->

-<typeCache mvcVersionId="cc73190b-ab9d-435c-8315-10ff295c572a" lastModified="2017/6/23 18:34:17">

-<assembly name="MVCTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">

-<module versionId="1949a001-c30a-4d56-ac65-d1714f608b76">

<type>MVCTest.Controllers.AccountController</type>

<type>MVCTest.Controllers.HomeController</type>

<type>MVCTest.Controllers.ManageController</type>

</module>

</assembly>

</typeCache>

Controller的释放很简单，直接上代码吧。

/// <summary>Releases the specified controller.</summary>
/// <param name="controller">The controller to release.</param>
public virtual void ReleaseController(IController controller)
{
    IDisposable disposable = controller as IDisposable;
    if (disposable != null)
    {
        disposable.Dispose();
    }
}

由于所有的Controller类型都实现了IDisposable接口，所以我们可以直接调用当前Controller对象的Dispose方法即可。

四、小结

   好了，这篇文章就先写到这里吧，Controller的激活系统还没有完，今天只是从总体上来讲一下，内容很多，很难在一片文章里把所有东西都写到。这个概览先给大家一个整体上的感觉吧，下一篇文章就具体写一下Controller的激活解析过程。

写一写很不错，把自己的理解写出来，现在更清晰了，也希望高手来指正和赐教。