在上篇 mvc源码分析-Controllerl篇 TempData数据存储我们讲到了ActionInvoker.InvokeAction(ControllerContext, actionName) 这句，当时跳过了，现在我们首先来看看ActionInvoker属性的定义吧：
public IActionInvoker ActionInvoker {
get {
if (_actionInvoker == null) {
_actionInvoker = CreateActionInvoker();
}
return _actionInvoker;
}
set {
_actionInvoker = value;
}
}
protected virtual IActionInvoker CreateActionInvoker() {
return new ControllerActionInvoker();
}
和TempDataProvider属性定义一样，大家一定要习惯这些代码啊。
而ControllerActionInvoker的定义也很简单，但是这个类却不简单啊。
让我们来看看你InvokeAction的定义吧：
public virtual bool InvokeAction(ControllerContext controllerContext, string actionName) {if (controllerContext == null) {throw new ArgumentNullException("controllerContext");}if (String.IsNullOrEmpty(actionName)) {throw new ArgumentException(mon_NullOrEmpty, "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 requestInvokeActionResult(controllerContext, authContext.Result);}else {if (controllerContext.Controller.ValidateRequest) {ValidateRequest(controllerContext);}IDictionary<string, object> parameters = GetParameterValues(controllerContext, actionDescriptor);ActionExecutedContext postActionContext = InvokeActionMethodWithFilters(controllerContext, filterInfo.ActionFilters, actionDescriptor, parameters);InvokeActionResultWithFilters(controllerContext, filterInfo.ResultFilters, postActionContext.Result);}}catch (ThreadAbortException) {// This type of exception occurs as a result of Response.Redirect(), but we special-case so that// the filters don't see this as an error.throw;}catch (Exception ex) {// something blew up, so execute the exception filtersExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex);if (!exceptionContext.ExceptionHandled) {throw;}InvokeActionResult(controllerContext, exceptionContext.Result);}return true;}// notify controller that no method matchedreturn false;}
这个方法里面的内容不可能一次讲完的，我们看看 ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext);很明显ControllerDescriptor是Controller实例的一个包装类。 protected virtual ControllerDescriptor GetControllerDescriptor(ControllerContext controllerContext) {
Type controllerType = controllerContext.Controller.GetType();
ControllerDescriptor controllerDescriptor = DescriptorCache.GetDescriptor(controllerType, () => new ReflectedControllerDescriptor(controllerType));
return controllerDescriptor;
}
从这个方法中，我们可以知道实际返回的是一个ReflectedControllerDescriptor实例，它是ControllerDescriptor的子类，DescriptorCache.GetDescriptor（...）好像是从缓存中获取的啊，让我们证实一下吧，先来看看ControllerDescriptorCache的GetDescriptor方法：
internal sealed class ControllerDescriptorCache : ReaderWriterCache<Type, ControllerDescriptor> {
public ControllerDescriptor GetDescriptor(Type controllerType, Func<ControllerDescriptor> creator) {
return FetchOrCreateItem(controllerType, creator);
}
}
FetchOrCreateItem方法很简单，从缓存中获取ControllerDescriptor ，如果没有就创建并加入缓存然后在返回，缓存实现方式其实就是一个字典Dictionary<TKey, TValue>。
现在看看ReflectedControllerDescriptor的够着函数是否有什么特别之处：
_controllerType = controllerType;
_selector = new ActionMethodSelector(_controllerType);
怎么又有ActionMethodSelector这个东东啊，其构造函数如下
public ActionMethodSelector(Type controllerType) {
ControllerType = controllerType;
PopulateLookupTables();
}
private void PopulateLookupTables() {
MethodInfo[] allMethods = ControllerType.GetMethods(BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public);
MethodInfo[] actionMethods = Array.FindAll(allMethods, IsValidActionMethod);
AliasedMethods = Array.FindAll(actionMethods, IsMethodDecoratedWithAliasingAttribute);
NonAliasedMethods = actionMethods.Except(AliasedMethods).ToLookup(method => method.Name, StringComparer.OrdinalIgnoreCase);
}
这个方法很简单，找出ControllerType的所有实例、共有方法，然后在过滤调不是Action的，最后吧这些Action方法分成两部分，一部分有别名，一部分没有别名。
现在我们已经得到了ControllerDescriptor实例，下面应该来看看ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName);这句代码了；同样我们可以确认ActionDescriptor实际上一个Action的包装类。
protected virtual ActionDescriptor FindAction(ControllerContext controllerContext, ControllerDescriptor controllerDescriptor, string actionName)这个方法实际上就是调用
ControllerDescriptor类FindAction方法，让我们看看你ReflectedControllerDescriptor的FindAction方法，该方法很简单，组要就2句代码：
MethodInfo matched = _selector.FindActionMethod(controllerContext, actionName);
return new ReflectedActionDescriptor(matched, actionName, this);
_selector.FindActionMethod(controllerContext, actionName);这句就是找到我们需要Action对应的MethodInfo。
public MethodInfo FindActionMethod(ControllerContext controllerContext, string actionName) {List<MethodInfo> methodsMatchingName = GetMatchingAliasedMethods(controllerContext, actionName);methodsMatchingName.AddRange(NonAliasedMethods[actionName]);List<MethodInfo> finalMethods = RunSelectionFilters(controllerContext, methodsMatchingName);switch (finalMethods.Count) {case 0:return null;case 1:return finalMethods[0];default:throw CreateAmbiguousMatchException(finalMethods, actionName);}}
默认情况下，我们的Action是没有别名的List<MethodInfo> methodsMatchingName = GetMatchingAliasedMethods(controllerContext, actionName);这句执行后是没有什么结果的，而RunSelectionFilters的实现比较特别
private static List<MethodInfo> RunSelectionFilters(ControllerContext controllerContext, List<MethodInfo> methodInfos) {// remove all methods which are opting out of this request// to opt out, at least one attribute defined on the method must return falseList<MethodInfo> matchesWithSelectionAttributes = new List<MethodInfo>();List<MethodInfo> matchesWithoutSelectionAttributes = new List<MethodInfo>();foreach (MethodInfo methodInfo in methodInfos) {ICollection<ActionMethodSelectorAttribute> attrs = ReflectedAttributeCache.GetActionMethodSelectorAttributes(methodInfo);if (attrs.Count == 0) {matchesWithoutSelectionAttributes.Add(methodInfo);}else if (attrs.All(attr => attr.IsValidForRequest(controllerContext, methodInfo))) {matchesWithSelectionAttributes.Add(methodInfo);}}// if a matching action method had a selection attribute, consider it more specific than a matching action method// without a selection attributereturn (matchesWithSelectionAttributes.Count > 0) ? matchesWithSelectionAttributes : matchesWithoutSelectionAttributes;}
循环每个MethodInfo，查找它们的自定义的ActionMethodSelectorAttribute特性，如果有只返回验证通过的特性。看到ReflectedAttributeCache.GetActionMethodSelectorAttributes(methodInfo)这样的代码感觉由于缓存有关，
private static ReadOnlyCollection<TAttribute> GetAttributes<TMemberInfo, TAttribute>(ConcurrentDictionary<TMemberInfo, ReadOnlyCollection<TAttribute>> lookup, TMemberInfo memberInfo)
where TAttribute : Attribute
where TMemberInfo : MemberInfo {
return lookup.GetOrAdd(memberInfo, mi => new ReadOnlyCollection<TAttribute>((TAttribute[])memberInfo.GetCustomAttributes(typeof(TAttribute), inherit: true)));
}
ReflectedAttributeCache这个类有几个缓存字典：
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<ActionMethodSelectorAttribute>>
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<ActionNameSelectorAttribute>>
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<FilterAttribute>>
ConcurrentDictionary<Type, ReadOnlyCollection<FilterAttribute>>
默认实现ActionMethodSelectorAttribute类主要有以下几个
AcceptVerbsAttribute
HttpDeleteAttribute
HttpGetAttribute
HttpPostAttribute
HttpPutAttribute
NonActionAttribute
AcceptVerbsAttribute
剩下的就是直接实例一个ReflectedActionDescriptor对象了，这个也没什么特殊，只是里面有一个验证方法
if (validateMethod) {
string failedMessage = VerifyActionMethodIsCallable(methodInfo);
if (failedMessage != null) {
throw new ArgumentException(failedMessage, "methodInfo");
}
}
用来验证该方法是否可以执行，以下几种情况经不会通过，（1）方法是静态方法（2）方法的实例类型不是ControllerBase（3）是否包含泛型参数如public ActionResult Index<T>()是非法的，但public ActionResult Index(List<string> aa)是合法（4）参数中不能含有Ref和out。
这篇文章说的很散，我们需要注意一点微软在mvc里面缓存做的很好了，在前面个将获取ControllerTyper时它是有缓存的，一次读取当前程序集所有的ControllerType，在这里提到了一个DescriptorCache 缓存每次调用的ControllerType->ReflectedControllerDescriptor，而ReflectedControllerDescriptor实例会一次去读该Controller的所有Action方法；这里还有一个ReflectedAttributeCache，缓存每次调用MethodInfo的所有特性（ActionMethodSelectorAttribute、ActionNameSelectorAttribute、FilterAttribute），当然FilterAttribute特性还可以在类上面。
