mvc源码解析(6)-获取ControllerType

   为什么要讲ControllerType？其实刚开始的时候并没有讲这个ControllerType的打算，但是在看mvc源码的时候，心里老是有个疙瘩，一直在琢磨ControllerType的含义，随着研究的深入才慢慢发现它的真正含义。ControllerType是出现在MvcHandler创建控制器的时候用到的：

controller = factory.CreateController(RequestContext, controllerName);

factory就是默认的DefaultControllerFactory的对象，我们可来看看CreateController的定义：

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");             }             Type controllerType = GetControllerType(requestContext, controllerName);             IController controller = GetControllerInstance(requestContext, controllerType);             return controller;         }

在创建controller之前，会根据当前的请求上下文和控制器的名称来获取controllerType，controllerType里面包含命名空间在内的Controller的具体信息。获取的ControllerType最终返回的是GetControllerTypeWithinNamespaces方法返回的值，具体实现如下：

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);                  }         }

 看到红色的代码我们可以猜到是在由ControllerTypeCache建立的缓存中直接将匹配的matchingTypes取出来，我们直接看里面的方法实现吧：

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;         }

 在这句代码中我也要注意一点:我们请求的controller所在的命名空间存储HashSet<String>中，而我们每次请求一次Action的时候，会将当前Action所在的Controller的名称和Controller所在的命名空间缓存在 ILookup<string, Type>中。我们来看红色代码IsNamespaceMatch方法，判断请求的controller所在的命名空间与目标命名空间是否一致，具体的方法实现如下：

internal static bool IsNamespaceMatch(string requestedNamespace, string targetNamespace) {                           // degenerate cases                          if (requestedNamespace == null) {return false;}                          else if (requestedNamespace.Length == 0) {return true;}             if (!requestedNamespace.EndsWith(".*", StringComparison.OrdinalIgnoreCase)) {                    // looking for exact namespace match                                   return String.Equals(requestedNamespace, targetNamespace, StringComparison.OrdinalIgnoreCase);}                         else {                    // looking for exact or sub-namespace match                                    requestedNamespace = requestedNamespace.Substring(0, requestedNamespace.Length - ".*".Length);                                    if (!targetNamespace.StartsWith(requestedNamespace, StringComparison.OrdinalIgnoreCase)) {return false;}                    if (requestedNamespace.Length == targetNamespace.Length)                        {                               // exact match                                 return true;                                        }                                      else if (targetNamespace[requestedNamespace.Length] == '.') {                                    // good prefix match, e.g. requestedNamespace = "Foo.Bar" and targetNamespace = "Foo.Bar.Baz"                                                         return true;                                           }                                      else {                                                      // bad prefix match, e.g. requestedNamespace = "Foo.Bar" and targetNamespace = "Foo.Bar2"                                                      return false;                                             }                                 }                       }

判断的具体逻辑我们不做详解,我们回到这么一句：

ICollection<Type> matchingTypes = ControllerTypeCache.GetControllerTypes(controllerName, namespaces);

 获取到ControllerType之后，判断集合matchingTypes中找到的ControllerType的数量，如有一个则直接返回，如有多个匹配的项,则抛出异常。很显然，在同一个命名空间下不能有相同名称的Controller。这样我们就获取到了具体的ControllerType对象。