asp.net mvc源码分析Controllerl篇 如何创建Controller实例

在上一篇文章asp.net mvc源码分析-路由篇 如何找到 IHttpHandler中最后提到了MvcHandler，来上我们看看它的定义

 public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState

它有几个比较重要的属性：

internal ControllerBuilder ControllerBuilder  ，ControllerBuilder 类主要负责创建IControllerFactory

public RequestContext RequestContext，RequestContext是对这次请求的HttpContext（httpContext类）和RouteData的包装

而它的BeginProcessRequest方法中有几句比较重要的代码：

IControllerFactory factory;
ProcessRequestInit(httpContext, out controller, out factory);
IAsyncController asyncController = controller as IAsyncController;
if (asyncController != null) {
}
else
{
  Action action = delegate {
                        try {
                            controller.Execute(RequestContext);
                        }
                        finally {
                            factory.ReleaseController(controller);
                        }
 return AsyncResultWrapper.BeginSynchronous(callback, state, action, _processRequestTag);
}

在这篇文章中我们主要关心ProcessRequestInit(httpContext, out controller, out factory);    如何创建controller

ProcessRequestInit方法大致如下：

  private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) {
            string controllerName = RequestContext.RouteData.GetRequiredString("controller");
            factory = ControllerBuilder.GetControllerFactory();
            controller = factory.CreateController(RequestContext, controllerName);
  }

         string controllerName = RequestContext.RouteData.GetRequiredString("controller");这句很简单获取Controller的名称，RouteData是当前路由数据，里面的key包括我们注册是的url格式  "{controller}/{action}/{id}",  和默认的defaults=new { controller = "Home", action = "Index", id = UrlParameter.Optional } 

现在大家知道为什么了我上一篇文章提到{controller}/{action}是必须得了吧。

现在让我们来看看ControllerBuilder的主要代码：

 public ControllerBuilder()
            : this(null) {
        }

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

        public static ControllerBuilder Current {
            get {
                return _instance;
            }
        }  
public IControllerFactory GetControllerFactory() {
            return _serviceResolver.Current;
        }

        public void SetControllerFactory(IControllerFactory controllerFactory) {
            if (controllerFactory == null) {
                throw new ArgumentNullException("controllerFactory");
            }

            _factoryThunk = () => controllerFactory;
        }

        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,
                        controllerFactoryType),
                    "controllerFactoryType");
            }

            _factoryThunk = delegate() {
                try {
                    return (IControllerFactory)Activator.CreateInstance(controllerFactoryType);
                }
                catch (Exception ex) {
                    throw new InvalidOperationException(
                        String.Format(
                            CultureInfo.CurrentCulture,
                            MvcResources.ControllerBuilder_ErrorCreatingControllerFactory,
                            controllerFactoryType),
                        ex);
                }
            };
        }

　　由以上代码我们可以知道如果没有调用ControllerBuilder的SetControllerFactory方法那我们就用默认的DefaultControllerFactory，如果设置了我们就可以用我们自己ControllerFactory。如果项目有需要实现自己的ControllerFactory，那么我们可以Global.asax.cs的 protected void Application_Start()方法调用 ControllerBuilder.Current.SetControllerFactory(xxx); 

让我们来看看DefaultControllerFactory是怎么创建的：

  internal DefaultControllerFactory(IControllerActivator controllerActivator, IResolver<IControllerActivator> activatorResolver, IDependencyResolver dependencyResolver) {
            if (controllerActivator != null) {
                _controllerActivator = controllerActivator;
            }
            else {
                _activatorResolver = activatorResolver ?? new SingleServiceResolver<IControllerActivator>(
                    () => null,
                    new DefaultControllerActivator(dependencyResolver),
                    "DefaultControllerFactory contstructor"
                );
            }
        }

这里我们涉及到一个IControllerActivator接口，默认情况下用的是DefaultControllerActivator类，

现在我们已经得到了ControllerFactory，再看看它是怎么创建Controller的，说白了就是DefaultControllerFactory的CreateController方法

 public virtual IController CreateController(RequestContext requestContext, string controllerName) {
    。。
            Type controllerType = GetControllerType(requestContext, controllerName);
            IController controller = GetControllerInstance(requestContext, controllerType);
            return controller;
        }

默认我们是没有namespaces，而GetControllerType(requestContext, controllerName)主要是调用 GetControllerTypeWithinNamespaces(requestContext.RouteData.Route, controllerName, null /* namespaces */)

  private Type GetControllerTypeWithinNamespaces(RouteBase route, string controllerName, HashSet<string> namespaces) {
            // Once the master list of controllers has been created we can quickly index into it
            ControllerTypeCache.EnsureInitialized(BuildManager);

            ICollection<Type> matchingTypes = ControllerTypeCache.GetControllerTypes(controllerName, namespaces);
            switch (matchingTypes.Count) {
                case 0:
                    // no matching types
                    return null;

                case 1:
                    // single matching type
                    return matchingTypes.First();

                default:
                    // multiple matching types
                    throw CreateAmbiguousControllerException(route, controllerName, matchingTypes);
            }
        }

这里面主要涉及到一个ControllerTypeCache，它负责缓存当前程序中所有的Controller。

让我们看看ControllerTypeCache的主要方法吧

public void EnsureInitialized(IBuildManager buildManager) {
            if (_cache == null) {
                lock (_lockObj) {
                    if (_cache == null) {
                        List<Type> controllerTypes = TypeCacheUtil.GetFilteredTypesFromAssemblies(_typeCacheName, IsControllerType, buildManager);
                        var groupedByName = controllerTypes.GroupBy(
                            t => t.Name.Substring(0, t.Name.Length - "Controller".Length),
                            StringComparer.OrdinalIgnoreCase);
                        _cache = groupedByName.ToDictionary(
                            g => g.Key,
                            g => g.ToLookup(t => t.Namespace ?? String.Empty, StringComparer.OrdinalIgnoreCase),
                            StringComparer.OrdinalIgnoreCase);
                    }
                }
            }
        }
  internal static bool IsControllerType(Type t) {
            return
                t != null &&
                t.IsPublic &&
                t.Name.EndsWith("Controller", StringComparison.OrdinalIgnoreCase) &&
                !t.IsAbstract &&
                typeof(IController).IsAssignableFrom(t);
        }
 public ICollection<Type> GetControllerTypes(string controllerName, HashSet<string> namespaces) {
            HashSet<Type> matchingTypes = new HashSet<Type>();
            ILookup<string, Type> nsLookup;
            if (_cache.TryGetValue(controllerName, out nsLookup)) {
                // this friendly name was located in the cache, now cycle through namespaces
                if (namespaces != null) {
                    foreach (string requestedNamespace in namespaces) {
                        foreach (var targetNamespaceGrouping in nsLookup) {
                            if (IsNamespaceMatch(requestedNamespace, targetNamespaceGrouping.Key)) {
                                matchingTypes.UnionWith(targetNamespaceGrouping);
                            }
                        }
                    }
                }
                else {
                    // if the namespaces parameter is null, search *every* namespace
                    foreach (var nsGroup in nsLookup) {
                        matchingTypes.UnionWith(nsGroup);
                    }
                }
            }
            return matchingTypes;
        }

 List<Type> controllerTypes = TypeCacheUtil.GetFilteredTypesFromAssemblies(_typeCacheName, IsControllerType, buildManager);这句代码就是用来查询当前程序的类，这个类必须通过IsControllerType方法的验证（类是共有非抽象继承于IController且类名Controller结尾），而这个_cache是个Dictionary<string, ILookup<string, Type>>类型的数据。
现在我们已经得到了ControllerType，来看看 IController controller = GetControllerInstance(requestContext, controllerType);吧里面主要就一句
 ControllerActivator.Create(requestContext, controllerType);而ControllerActivator就是先前的DefaultControllerActivator，DefaultControllerActivator的代码如下：

private class DefaultControllerActivator : IControllerActivator {
            Func<IDependencyResolver> _resolverThunk;
            public DefaultControllerActivator()
                : this(null) {
            }
            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);
                }
            }
        }

　这里的_resolverThunk()来源于DependencyResolver.Current，
private static DependencyResolver _instance = new DependencyResolver();
        public static IDependencyResolver Current {
            get {
                return _instance.InnerCurrent;
            }
        }
 private IDependencyResolver _current = new DefaultDependencyResolver();
        public IDependencyResolver InnerCurrent {
            get {
                return _current;
            }
        }
所以真正创建controller是在DefaultDependencyResolver的GetService方法，核心代码   return Activator.CreateInstance(serviceType);
这篇文件扯得比较远，可见创建Controller是多么的麻烦啊。阅读源代码主要是让我们理解其逻辑，同时也让我们学习其开发的思想。
本文讲的这么多，在项目中最常用的就是ControllerBuilder.Current.SetControllerFactory(xxx);  只要大家理解了它就可以了。