ASP.NET MVC学习笔记-MVC运行机制之源码剖析

 学习ASP.NET MVC已经有段时间了，以前都是断断续续的了解了下， 对于ASP.NET MVC路由及运行机制一直不是很了解, 在网络上找了好多资料无非都是讲解了下如何添加ASP.NET MVC路由及创建自定义视图引挚等. 因此最近这几天, 下载了ASP.NET MVC源码好好研究了一翻, 将其运行机制记录下来, 一来整理下自己的理解思路, 加强自己的理解, 二来也希望对学习ASP.NET的后来者有所帮助, 文中都是自我理解, 有错误之处望高手能帮忙纠正之!!

我们都知道ASP.NET首先是从Global.aspx中开始运行的, 在Application_Start()中添加路由映射后, 就由URLRouting组件创建IRouteHandler并执行, 在ASP.NET MVC默认情况下是MvcRouteHandler(关于自定义RouteHandler, 请参考其他的相关文章), 我们先看看MvcRouteHandler的源码:

public class MvcRouteHandler : IRouteHandler { protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext) { return new MvcHandler(requestContext); } #region IRouteHandler Members IHttpHandler IRouteHandler.GetHttpHandler(RequestContext requestContext) { return GetHttpHandler(requestContext); } #endregion }

 

从源码里我们可以看出,MvcRouteHandler返回了MvcHandler实例并传递RequestContext参数,  然后转到MvcHandler的ProcessRequest(HttpContext httpContext)方法中, 并在这个方法里根据httpContext创建了HttpContextWrapper(继承于HttpContextBase)实例, 源码如下:

protected internal virtual void ProcessRequest(HttpContextBase httpContext) { AddVersionHeader(httpContext); // Get the controller type string controllerName = RequestContext.RouteData.GetRequiredString("controller"); // Instantiate the controller and call Execute IControllerFactory factory = ControllerBuilder.GetControllerFactory(); IController controller = factory.CreateController(RequestContext, controllerName); if (controller == null) { throw new InvalidOperationException( String.Format( CultureInfo.CurrentUICulture, MvcResources.ControllerBuilder_FactoryReturnedNull, factory.GetType(), controllerName)); } try { controller.Execute(RequestContext); } finally { factory.ReleaseController(controller); } }

 

Controller解析执行就是从这里开始的了,是ASP.NET MVC处理请求的关键部分, 我们现在逐条分析代码,根据执行顺序一步一步揭开它神秘的面纱, 首先看看ControllerBuilder类部分代码:

public class ControllerBuilder { private Func<IControllerFactory> _factoryThunk; private static ControllerBuilder _instance = new ControllerBuilder(); private HashSet<string> _namespaces = new HashSet<string>(StringComparer.OrdinalIgnoreCase); public ControllerBuilder() { SetControllerFactory(new DefaultControllerFactory() { ControllerBuilder = this }); } public static ControllerBuilder Current { get { return _instance; } } [SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate", Justification = "Calling method multiple times might return different objects.")] public IControllerFactory GetControllerFactory() { IControllerFactory controllerFactoryInstance = _factoryThunk(); return controllerFactoryInstance; } public void SetControllerFactory(IControllerFactory controllerFactory) { if (controllerFactory == null) { throw new ArgumentNullException("controllerFactory"); } _factoryThunk = () => controllerFactory; } }

 

默认情况下ControllerBuilder.GetControllerFactory()是返回的DefaultControllerFactory实例,接着再往下看:
 IController controller = factory.CreateController(RequestContext, controllerName);
它是如何创建controller的呢?　看看的DefaultControllerFactory源码就知道了.
public virtual IController CreateController(RequestContext requestContext, string controllerName) { if (requestContext == null) { throw new ArgumentNullException("requestContext"); } if (String.IsNullOrEmpty(controllerName)) { throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName"); } RequestContext = requestContext; Type controllerType = GetControllerType(controllerName); IController controller = GetControllerInstance(controllerType); return controller; }

 

这里调用了GetControllerType()和GetControllerInstance()方法来创建controller,在GetControllerType方法中主要是一行代码:return GetControllerTypeWithinNamespaces(controllerName, null /* namespaces */);那我们也看看它做了些什么动作.
private Type GetControllerTypeWithinNamespaces(string controllerName, HashSet<string> namespaces) { // Once the master list of controllers has been created we can quickly index into it ControllerTypeCache.EnsureInitialized(BuildManager); IList<Type> matchingTypes = ControllerTypeCache.GetControllerTypes(controllerName, namespaces); ... }

 

它主要是调用了ControllerTypeCache中的两个方法,在EnsureInitialized方法中调用了GetAllControllerTypes(BuildManager)方法从BuildManager中获取所有程序集中public, not abstract并且以"Controller"结尾的Type放入列表中进行缓存,ControllerTypeCache.GetControllerTypes(controllerName, namespaces)主要是从缓存的字典中读取对应的Controller.
接着在GetControllerInstance方法中调用Activator.CreateInstance静态方法创建Controller, 然后执行Controller的Execute方法,Execute方法是IController接口中定义的方法, ControllerBase类实现了此方法并提供了TempData和ViewData属性, Execute实现如下:
protected virtual void Execute(RequestContext requestContext) { if (requestContext == null) { throw new ArgumentNullException("requestContext"); } Initialize(requestContext); ExecuteCore(); }

 

Initialize方法根据RequestContext创建了ControllerContext对象, ControllerContext有4个属性:
        public virtual ControllerBase Controller;                //初始化时传入
        public virtual HttpContextBase HttpContext;            //默认为RequestContext.HttpContext或EmptyHttpContext
        public RequestContext RequestContext ;                //初始化时传入
        public virtual RouteData RouteData;                //默认为RequestContext.RouteData
ExecuteCore()是ControllerBase的抽象方法,Controller类实现了此方法,实现如下:

protected override void ExecuteCore() { TempData.Load(ControllerContext, TempDataProvider); try { string actionName = RouteData.GetRequiredString("action"); if (!ActionInvoker.InvokeAction(ControllerContext, actionName)) { HandleUnknownAction(actionName); } } finally { TempData.Save(ControllerContext, TempDataProvider); } }

 

在ExecuteCore()中实现了TempData的Load和Save, 所以TempData才可以在其他的View中有效,而ViewData只能在对应的View中有效. ActionInvoker是Controller中的属性, 其默认为ControllerActionInvoker实例, 我们接着再看看ActionInvoker.InvokeAction(ControllerContext, actionName)又是怎么找到Action的呢? 还是从源码入手:
public virtual bool InvokeAction(ControllerContext controllerContext, string actionName) { ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext); ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName); if (actionDescriptor != null) { FilterInfo filterInfo = GetFilters(controllerContext, actionDescriptor); try { AuthorizationContext authContext = InvokeAuthorizationFilters(controllerContext, filterInfo.AuthorizationFilters, actionDescriptor); if (authContext.Result != null) { // the auth filter signaled that we should let it short-circuit the request InvokeActionResult(controllerContext, authContext.Result); } else { if (controllerContext.Controller.ValidateRequest) { ValidateRequest(controllerContext.HttpContext.Request); } IDictionary<string, object> parameters = GetParameterValues(controllerContext, actionDescriptor); ActionExecutedContext postActionContext = InvokeActionMethodWithFilters(controllerContext, filterInfo.ActionFilters, actionDescriptor, parameters); InvokeActionResultWithFilters(controllerContext, filterInfo.ResultFilters, postActionContext.Result); } } return true; } // notify controller that no method matched return false; }

 

GetControllerDescriptor(controllerContext)方法调用DescriptorCache.GetDescriptor()并返回了ReflectedControllerDescriptor(继承于ControllerDescriptor)实例,并在其Cache属性中保存了ReflectedControllerDescriptor实例. ReflectedControllerDescriptor类中有一个ActionMethodSelector类型的私用变量_selector, 在ActionMethodSelector构造方法中调用ControllerType.GetMethods方法得到了Controller中的所有方法并过滤出Action方法存储到AliasedMethods和NonAliasedMethods属性中, 用于查询Action.而FindAction(controllerContext, controllerDescriptor, actionName)最终也是调用了ControllerDescriptor中的FindAction(),而这里的ControllerDescriptor始终是ReflectedControllerDescriptor, 所以我们找到ReflectedControllerDescriptor的FindAction方法:
public override ActionDescriptor FindAction(ControllerContext controllerContext, string actionName) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } if (String.IsNullOrEmpty(actionName)) { throw new ArgumentException(MvcResources.Common_NullOrEmpty, "actionName"); } MethodInfo matched = _selector.FindActionMethod(controllerContext, actionName); if (matched == null) { return null; } return new ReflectedActionDescriptor(matched, actionName, this); }

 

可以看出, 它是调用ActionMethodSelector的FindActionMethod然后构造新的ReflectActionDescriptor返回的,在ActionMethodSelector的FindActionMethod方法里就用到了刚才提到了AliasedMethods和NonAliasedMethods属性找出相匹配的方法, 再回到InvokeAction继续往下看执行的是GetFilters将controller添加到4个基本Filter列表中去:
protected virtual FilterInfo GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor) { FilterInfo filters = actionDescriptor.GetFilters(); // if the current controller implements one of the filter interfaces, it should be added to the list at position 0 ControllerBase controller = controllerContext.Controller; AddControllerToFilterList(controller, filters.ActionFilters); AddControllerToFilterList(controller, filters.ResultFilters); AddControllerToFilterList(controller, filters.AuthorizationFilters); AddControllerToFilterList(controller, filters.ExceptionFilters); return filters; }

 

FilterInfo类只有四个List属性, 分别是:
        public IList<IActionFilter> ActionFilters;
        public IList<IAuthorizationFilter> AuthorizationFilters;
        public IList<IExceptionFilter> ExceptionFilters;
        public IList<IResultFilter> ResultFilters;

再接着执行GetParameterValues(controllerContext, actionDescriptor), 在这个方法里获取Action参数并实现Model绑定,GetParameterValue代码如下:
protected virtual object GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) { // collect all of the necessary binding properties Type parameterType = parameterDescriptor.ParameterType; IModelBinder binder = GetModelBinder(parameterDescriptor); IDictionary<string, ValueProviderResult> valueProvider = controllerContext.Controller.ValueProvider; string parameterName = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName; Predicate<string> propertyFilter = GetPropertyFilter(parameterDescriptor); // finally, call into the binder ModelBindingContext bindingContext = new ModelBindingContext() { FallbackToEmptyPrefix = (parameterDescriptor.BindingInfo.Prefix == null), // only fall back if prefix not specified ModelName = parameterName, ModelState = controllerContext.Controller.ViewData.ModelState, ModelType = parameterType, PropertyFilter = propertyFilter, ValueProvider = valueProvider }; object result = binder.BindModel(controllerContext, bindingContext); return result; }

 

接着由InvokeActionMethodWithFilters转到InvokeActionMethodFilter执行filter.OnActionExecuting(即controller),然后从InvokeActionMethodf中执行ActionDescriptor的抽象方法Execute()并创建ActionResult返回.
在Execute方法中会创建ActionMethodDispatcher对象, 在ActionMethodDispatcher构造函数中传入Aciton方法, 再调用ActionMethodDispatcher的Execute进入具体的Action方法(即Controller的Action方法), 现由Controller的View方法创建ViewResult对象返回:
protected internal virtual ViewResult View(string viewName, string masterName, object model) { if (model != null) { ViewData.Model = model; } return new ViewResult { ViewName = viewName, MasterName = masterName, ViewData = ViewData, TempData = TempData }; }

 

到此Action执行结束, 执OnActionExecuted()方法,再回到InvokeAction执行InvokeActionResultWithFilters, 这时OnResultExecuting()就开始运行了,OnResultExecuting执行完了后, 就执行ActionResult.ExecuteResult, 从上面代码可以知道View方法返回的是ViewResult,ExecuteResult是在ActionResult类中定义的抽象方法, ViewResultBase实现了此方法查找ViewEngine及对View调用Render.
public override void ExecuteResult(ControllerContext context) { if (context == null) { throw new ArgumentNullException("context"); } if (String.IsNullOrEmpty(ViewName)) { ViewName = context.RouteData.GetRequiredString("action"); } ViewEngineResult result = null; if (View == null) { result = FindView(context); View = result.View; } ViewContext viewContext = new ViewContext(context, View, ViewData, TempData); View.Render(viewContext, context.HttpContext.Response.Output); if (result != null) { result.ViewEngine.ReleaseView(context, View); } }

 

FindView是ViewResultBase中定义的抽象方法,在ViewResult中的实现如下:    

protected override ViewEngineResult FindView(ControllerContext context) { ViewEngineResult result = ViewEngineCollection.FindView(context, ViewName, MasterName); if (result.View != null) { return result; } // we need to generate an exception containing all the locations we searched StringBuilder locationsText = new StringBuilder(); foreach (string location in result.SearchedLocations) { locationsText.AppendLine(); locationsText.Append(location); } throw new InvalidOperationException(String.Format(CultureInfo.CurrentUICulture, MvcResources.Common_ViewNotFound, ViewName, locationsText)); }

 

调用了ViewEngineCollection.FindView, ViewEngineCollection是ViewResultBase中的属性:

public ViewEngineCollection ViewEngineCollection { get { return _viewEngineCollection ?? ViewEngines.Engines; } set { _viewEngineCollection = value; } }

 

默认情况下是ViewEngines的静态属性Engines, 所以在自定义视图引挚时, 我们一般都会在Globol.cs中的Application_Start()中将自己定义的视图引挚添加到ViewEngines.Engines中去, ASP.NET MVC默认情况下就有new WebFormViewEngine().

public static class ViewEngines { private readonly static ViewEngineCollection _engines = new ViewEngineCollection { new WebFormViewEngine() }; public static ViewEngineCollection Engines { get { return _engines; } } }

 

WebFromViewEngine继承于VirtualPathProviderViewEngine, 而VirtualPathProviderViewEngine继承了IViewEngine, 并实现了IViewEngine的FindView,FindPartialView及ReleaseView, 还提供了MasterLocaltionFormats,PartialViewLocationFormats和ViewLocationFormats属性, 通常我们自定义的视图引挚可以继承于VirtualPathProviderViewEngine, ViewEngineCollection.FindView遍历所有的ViewEngine, 并调用ViewEngine.FindView根据返回的字符串数组创建ViewEngineResult对象返回, 默认情况下ViewEngineCollection只有一个ViewEngine(WebFromViewEngine), 所以我们找到VirtualPathProviderViewEngine的FindView实现:
public virtual ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache) { string[] viewLocationsSearched; string[] masterLocationsSearched; string controllerName = controllerContext.RouteData.GetRequiredString("controller"); string viewPath = GetPath(controllerContext, ViewLocationFormats, "ViewLocationFormats", viewName, controllerName, _cacheKeyPrefix_View, useCache, out viewLocationsSearched); string masterPath = GetPath(controllerContext, MasterLocationFormats, "MasterLocationFormats", masterName, controllerName, _cacheKeyPrefix_Master, useCache, out masterLocationsSearched); if (String.IsNullOrEmpty(viewPath) || (String.IsNullOrEmpty(masterPath) && !String.IsNullOrEmpty(masterName))) { return new ViewEngineResult(viewLocationsSearched.Union(masterLocationsSearched)); } return new ViewEngineResult(CreateView(controllerContext, viewPath, masterPath), this); }

 

GetPath根据ViewLocationFormats数据顺序查找到第一个符合条件的就返回, CreateView是VirtualPathProviderViewEngine提供的抽象函数, 需要在自定义的ViewEngine中实现, WebFormViewEngine实现如下:
protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath) { return new WebFormView(viewPath, masterPath); }

 

ViewEngineResult类中只包含了三个属性:
        public IEnumerable<string> SearchedLocations;
        public IView View;
        public IViewEngine ViewEngine;

FindView后返回到ExecuteResult方法中执行View.Render方法并传入了ViewContext(ControllerContext, View, ViewData, TempData),在WebFormView.Render中创建ViewPage对象并输出,关键代码如下:
public virtual void Render(ViewContext viewContext, TextWriter writer) { object viewInstance = BuildManager.CreateInstanceFromVirtualPath(ViewPath, typeof(object)); ViewPage viewPage = viewInstance as ViewPage; if (viewPage != null) { RenderViewPage(viewContext, viewPage); return; } ViewUserControl viewUserControl = viewInstance as ViewUserControl; if (viewUserControl != null) { RenderViewUserControl(viewContext, viewUserControl); return; } throw new InvalidOperationException( String.Format( CultureInfo.CurrentUICulture, MvcResources.WebFormViewEngine_WrongViewBase, ViewPath)); } RenderViewPage(viewContext, viewPage)方法: private void RenderViewPage(ViewContext context, ViewPage page) { if (!String.IsNullOrEmpty(MasterPath)) { page.MasterLocation = MasterPath; } page.ViewData = context.ViewData; page.RenderView(context); }

 

代码page.ViewData = context.ViewData就将Controller的ViewData传递到ViewPage中了, 因此我们可以在aspx页面使用Controller中的ViewData,TempData属性实质返回的是ViewPage中的ViewContext.TempData. 在ViewPage.RenderView对HtmlHelper,AjaxHelper和UrlHelper进行初始化后,就调用ProcessRequest开始进行页面处理,如OnPreInit, OnPreRender事件等, 最后再执OnResultExecuted,整个ASP.NET MVC调用流程到此就结束了.