MVC Controller

先回顾下之前的MVC执行过程：

一个HttpRequest是如何被ASP.NET和ASP.NET MVC框架执行的：经过IIS和ASP.NET处理后，Core Routing会首先根据URL匹配物理路径上的文件，如果不能匹配则由核心路由模块执行路由，路由被匹配后，MvcRouteHandler会将这个请求“带入”MVC框架，执行Controller和Action。

 

Controller是如何被创建以及执行的呢？

我们看一下MVCRouteHander的源码：

namespace System.Web.Mvc
{
    public class MvcRouteHandler : IRouteHandler
    {
        private IControllerFactory _controllerFactory;

        public MvcRouteHandler()
        {
        }

        public MvcRouteHandler(IControllerFactory controllerFactory)
        {
            _controllerFactory = controllerFactory;
        }

        protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext)
        {
            requestContext.HttpContext.SetSessionStateBehavior(GetSessionStateBehavior(requestContext));
            return new MvcHandler(requestContext);
        }

        protected virtual SessionStateBehavior GetSessionStateBehavior(RequestContext requestContext)
        {
            string controllerName = (string)requestContext.RouteData.Values["controller"];
            if (String.IsNullOrWhiteSpace(controllerName))
            {
                throw new InvalidOperationException(MvcResources.MvcRouteHandler_RouteValuesHasNoController);
            }

            IControllerFactory controllerFactory = _controllerFactory ?? ControllerBuilder.Current.GetControllerFactory();
            return controllerFactory.GetControllerSessionBehavior(requestContext, controllerName);
        }

        #region IRouteHandler Members

        IHttpHandler IRouteHandler.GetHttpHandler(RequestContext requestContext)
        {
            return GetHttpHandler(requestContext);
        }

        #endregion
    }
}

MvcRouteHandler的实现仅仅是通过GetHttpHandler方法返回一个MvcHandler实例。

再来看一下MvcHandler的实现：

 

 

核心方法依然是ProcessRequest（异步版BeginProceessRequest）。

protected internal virtual void ProcessRequest(HttpContextBase httpContext)
        {
            IController controller;
            IControllerFactory factory;
            ProcessRequestInit(httpContext, out controller, out factory);

            try
            {
                controller.Execute(RequestContext);
            }
            finally
            {
                factory.ReleaseController(controller);
            }
        }

ProcessRequestInit方法实现了Controller的创建

private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
        {
            // If request validation has already been enabled, make it lazy. This allows attributes like [HttpPost] (which looks
            // at Request.Form) to work correctly without triggering full validation.
            // Tolerate null HttpContext for testing.
            HttpContext currentContext = HttpContext.Current;
            if (currentContext != null)
            {
                bool? isRequestValidationEnabled = ValidationUtility.IsValidationEnabled(currentContext);
                if (isRequestValidationEnabled == true)
                {
                    ValidationUtility.EnableDynamicValidation(currentContext);
                }
            }

            AddVersionHeader(httpContext);
            RemoveOptionalRoutingParameters();

            // Get the controller type
            string controllerName = RequestContext.RouteData.GetRequiredString("controller");

            // Instantiate the controller and call Execute
            factory = ControllerBuilder.GetControllerFactory();
            controller = factory.CreateController(RequestContext, controllerName);
            if (controller == null)
            {
                throw new InvalidOperationException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.ControllerBuilder_FactoryReturnedNull,
                        factory.GetType(),
                        controllerName));
            }
        }

MvcHandler从RouteData中获得controller名字负责创建一个ControllerBuilder的实例，并通过ControllerBuilder的GetControllerFactory返回一个IControllerFactory的实例，这个实例就是DefaultControllerFactory，它的 CreateController方法负责创建需要的Controller实例

 

// Get the controller type
string controllerName = RequestContext.RouteData.GetRequiredString("controller");
// Instantiate the controller and call Execute
factory = ControllerBuilder.GetControllerFactory();
controller = factory.CreateController(RequestContext, controllerName);

 

Controller的执行：

Controller继承自ControllerBase，而Controller又继承自IController，而IController的定义非常简单：

namespace System.Web.Mvc
{
    public interface IController
    {
        void Execute(RequestContext requestContext);
    }
}

只有一个Execute（）接口。从接口定义可以看出，当Controller被“调用”的时候，应该负责完成Execute方法，参数RequestContext封装了HttpContext。

打开Controller源文件并没有发现Execute（）方法的实现，那么它应该在ControllerBase中，查看ControllerBase发现，在，Execute在内部调用ExecuteCore，ExecuteCore作为一个抽象方法，延迟到Controller中实现。ControllerBase只提供了诸如TempData、ViewData等，Controller的ExecuteCore方法真正invoke了action机制，是action的入口。下面的代码是ExecuteCore的实现：

 

 protected override void ExecuteCore()
        {
            // If code in this method needs to be updated, please also check the BeginExecuteCore() and
            // EndExecuteCore() methods of AsyncController to see if that code also must be updated.

            PossiblyLoadTempData();
            try
            {
                string actionName = RouteData.GetRequiredString("action");
                if (!ActionInvoker.InvokeAction(ControllerContext, actionName))
                {
                    HandleUnknownAction(actionName);
                }
            }
            finally
            {
                PossiblySaveTempData();
            }
        }

 

可以看到RouteData在这里又提供了action参数，可以想象InvokeAction方法依靠这个action的名字调用action，并实现诸多验证机制