我们重点来看看这个InvokeInnerFilterAsync。
protected override async Task InvokeInnerFilterAsync() ???????{ ???????????var next = State.ActionBegin; ???????????var scope = Scope.Invoker; ???????????var state = (object)null; ???????????var isCompleted = false; ???????????while (!isCompleted) ???????????{ ???????????????await Next(ref next, ref scope, ref state, ref isCompleted); ???????????} ???????}似曾相识，它与ResourceInvoker的InvokeFilterPipelineAsync几乎是一模一样的。并且也有一个Next方法，里面也是一个大的switch语句，然后是很多case。
case State.ActionBegin: ???????????????????{ ???????????????????????var controllerContext = _controllerContext; ???????????????????????_cursor.Reset(); ???????????????????????_instance = _cacheEntry.ControllerFactory(controllerContext); ???????????????????????_arguments = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); ???????????????????????var task = BindArgumentsAsync(); ???????????????????????if (task.Status != TaskStatus.RanToCompletion) ???????????????????????{ ???????????????????????????next = State.ActionNext; ???????????????????????????return task; ???????????????????????} ???????????????????????goto case State.ActionNext; ???????????????????} ???????????????case State.ActionNext: ???????????????????{ ???????????????????????var current = _cursor.GetNextFilter<IActionFilter, IAsyncActionFilter>(); ???????????????????????if (current.FilterAsync != null) ???????????????????????{ ???????????????????????????if (_actionExecutingContext == null) ???????????????????????????{ ???????????????????????????????_actionExecutingContext = new ActionExecutingContext(_controllerContext, _filters, _arguments, _instance); ???????????????????????????} ???????????????????????????state = current.FilterAsync; ???????????????????????????goto case State.ActionAsyncBegin; ???????????????????????} ???????????????????????else if (current.Filter != null) ???????????????????????{ ???????????????????????????if (_actionExecutingContext == null) ???????????????????????????{ ???????????????????????????????_actionExecutingContext = new ActionExecutingContext(_controllerContext, _filters, _arguments, _instance); ???????????????????????????} ???????????????????????????state = current.Filter; ???????????????????????????goto case State.ActionSyncBegin; ???????????????????????} ???????????????????????else ???????????????????????{ ???????????????????????????goto case State.ActionInside; ???????????????????????} ???????????????????} ???????????????case State.ActionAsyncBegin: ???????????????????{ ???????????????????????Debug.Assert(state != null); ???????????????????????Debug.Assert(_actionExecutingContext != null); ???????????????????????var filter = (IAsyncActionFilter)state; ???????????????????????var actionExecutingContext = _actionExecutingContext; ???????????????????????_diagnosticSource.BeforeOnActionExecution(actionExecutingContext, filter); ???????????????????????var task = filter.OnActionExecutionAsync(actionExecutingContext, InvokeNextActionFilterAwaitedAsync); ???????????????????????if (task.Status != TaskStatus.RanToCompletion) ???????????????????????{ ???????????????????????????next = State.ActionAsyncEnd; ???????????????????????????return task; ???????????????????????} ???????????????????????goto case State.ActionAsyncEnd; ???????????????????} ???????????????case State.ActionAsyncEnd: ???????????????????{ ???????????????????????Debug.Assert(state != null); ???????????????????????Debug.Assert(_actionExecutingContext != null); ???????????????????????var filter = (IAsyncActionFilter)state; ???????????????????????if (_actionExecutedContext == null) ???????????????????????{ ???????????????????????????// If we get here then the filter didn‘t call ‘next‘ indicating a short circuit. ???????????????????????????_logger.ActionFilterShortCircuited(filter); ???????????????????????????_actionExecutedContext = new ActionExecutedContext( ???????????????????????????????_controllerContext, ???????????????????????????????_filters, ???????????????????????????????_instance) ???????????????????????????{ ???????????????????????????????Canceled = true, ???????????????????????????????Result = _actionExecutingContext.Result, ???????????????????????????}; ???????????????????????} ???????????????????????_diagnosticSource.AfterOnActionExecution(_actionExecutedContext, filter); ???????????????????????goto case State.ActionEnd; ???????????????????} ???????????????case State.ActionSyncBegin: ???????????????????{ ???????????????????????Debug.Assert(state != null); ???????????????????????Debug.Assert(_actionExecutingContext != null); ???????????????????????var filter = (IActionFilter)state; ???????????????????????var actionExecutingContext = _actionExecutingContext; ???????????????????????_diagnosticSource.BeforeOnActionExecuting(actionExecutingContext, filter); ???????????????????????filter.OnActionExecuting(actionExecutingContext); ???????????????????????_diagnosticSource.AfterOnActionExecuting(actionExecutingContext, filter); ???????????????????????if (actionExecutingContext.Result != null) ???????????????????????{ ???????????????????????????// Short-circuited by setting a result. ???????????????????????????_logger.ActionFilterShortCircuited(filter); ???????????????????????????_actionExecutedContext = new ActionExecutedContext( ???????????????????????????????_actionExecutingContext, ???????????????????????????????_filters, ???????????????????????????????_instance) ???????????????????????????{ ???????????????????????????????Canceled = true, ???????????????????????????????Result = _actionExecutingContext.Result, ???????????????????????????}; ???????????????????????????goto case State.ActionEnd; ???????????????????????} ???????????????????????var task = InvokeNextActionFilterAsync(); ???????????????????????if (task.Status != TaskStatus.RanToCompletion) ???????????????????????{ ???????????????????????????next = State.ActionSyncEnd; ???????????????????????????return task; ???????????????????????} ???????????????????????goto case State.ActionSyncEnd; ???????????????????} ???????????????case State.ActionSyncEnd: ???????????????????{ ???????????????????????Debug.Assert(state != null); ???????????????????????Debug.Assert(_actionExecutingContext != null); ???????????????????????Debug.Assert(_actionExecutedContext != null); ???????????????????????var filter = (IActionFilter)state; ???????????????????????var actionExecutedContext = _actionExecutedContext; ???????????????????????_diagnosticSource.BeforeOnActionExecuted(actionExecutedContext, filter); ???????????????????????filter.OnActionExecuted(actionExecutedContext); ???????????????????????_diagnosticSource.AfterOnActionExecuted(actionExecutedContext, filter); ???????????????????????goto case State.ActionEnd; ???????????????????}如果我们查看之前的部分，就会发现。在ResourceInvoker中的动作过滤器部分并没有真正的执行，而是调用了抽象方法InvokeInnerFilterAsync。
???case State.ActionBegin: ???????????????????????{ ???????????????????????????var task = InvokeInnerFilterAsync(); ???????????????????????????if (task.Status != TaskStatus.RanToCompletion) ???????????????????????????{ ???????????????????????????????next = State.ActionEnd; ???????????????????????????????return task; ???????????????????????????} ???????????????????????????????goto case State.ActionEnd; ???????????????????????} ???????????????????????case State.ActionEnd: ???????????????????????{ ???????????????????????????if (scope == Scope.Exception) ???????????????????????????{ ???????????????????????????????// If we‘re inside an exception filter, let‘s allow those filters to ‘unwind‘ before ???????????????????????????????// the result. ???????????????????????????????isCompleted = true; ???????????????????????????????return Task.CompletedTask; ???????????????????????????} ???????????????????????????????Debug.Assert(scope == Scope.Invoker || scope == Scope.Resource); ???????????????????????????goto case State.ResultBegin; ???????????????????????}也就是说，所有的ActionFilter终归到底是在ControlerActionInvoker中执行的。接着我们来看Next方法的后面部分。
case State.ActionInside: ???????????????????{ ?????????????????????????//关键在这里 ???????????????????????var task = InvokeActionMethodAsync(); ???????????????????????if (task.Status != TaskStatus.RanToCompletion) ???????????????????????{ ???????????????????????????next = State.ActionEnd; ???????????????????????????return task; ???????????????????????} ???????????????????????goto case State.ActionEnd; ???????????????????} ???????????????case State.ActionEnd: ???????????????????{ ???????????????????????if (scope == Scope.Action) ???????????????????????{ ???????????????????????????if (_actionExecutedContext == null) ???????????????????????????{ ???????????????????????????????_actionExecutedContext = new ActionExecutedContext(_controllerContext, _filters, _instance) ???????????????????????????????{ ???????????????????????????????????Result = _result, ???????????????????????????????}; ???????????????????????????} ???????????????????????????isCompleted = true; ???????????????????????????return Task.CompletedTask; ???????????????????????} ???????????????????????var actionExecutedContext = _actionExecutedContext; ???????????????????????Rethrow(actionExecutedContext); ???????????????????????if (actionExecutedContext != null) ???????????????????????{ ???????????????????????????_result = actionExecutedContext.Result; ???????????????????????} ???????????????????????isCompleted = true; ???????????????????????return Task.CompletedTask; ???????????????????} ???????????????default: ???????????????????throw new InvalidOperationException();关键应该是那个InvokeActionMethodAsync方法。
private async Task InvokeActionMethodAsync() ???????{ ???????????var controllerContext = _controllerContext; ???????????var executor = _cacheEntry.ActionMethodExecutor; ???????????var controller = _instance; ???????????var arguments = _arguments; ???????????var orderedArguments = PrepareArguments(arguments, executor); ???????????var diagnosticSource = _diagnosticSource; ???????????var logger = _logger; ???????????IActionResult result = null; ???????????try ???????????{ ???????????????diagnosticSource.BeforeActionMethod( ???????????????????controllerContext, ???????????????????arguments, ???????????????????controller); ???????????????logger.ActionMethodExecuting(controllerContext, orderedArguments); ?????????????????//关键从这开始 ???????????????var returnType = executor.MethodReturnType; ???????????????if (returnType == typeof(void)) ???????????????{ ???????????????????// Sync method returning void ???????????????????executor.Execute(controller, orderedArguments); ???????????????????result = new EmptyResult(); ???????????????} ???????????????else if (returnType == typeof(Task)) ???????????????{ ???????????????????// Async method returning Task ???????????????????// Avoid extra allocations by calling Execute rather than ExecuteAsync and casting to Task. ???????????????????await (Task)executor.Execute(controller, orderedArguments); ???????????????????result = new EmptyResult(); ???????????????} ???????????????else if (returnType == typeof(Task<IActionResult>)) ???????????????{ ???????????????????// Async method returning Task<IActionResult> ???????????????????// Avoid extra allocations by calling Execute rather than ExecuteAsync and casting to Task<IActionResult>. ???????????????????result = await (Task<IActionResult>)executor.Execute(controller, orderedArguments); ???????????????????if (result == null) ???????????????????{ ???????????????????????throw new InvalidOperationException( ???????????????????????????Resources.FormatActionResult_ActionReturnValueCannotBeNull(typeof(IActionResult))); ???????????????????} ???????????????} ???????????????else if (IsResultIActionResult(executor)) ???????????????{ ???????????????????if (executor.IsMethodAsync) ???????????????????{ ???????????????????????// Async method returning awaitable-of-IActionResult (e.g., Task<ViewResult>) ???????????????????????// We have to use ExecuteAsync because we don‘t know the awaitable‘s type at compile time. ???????????????????????result = (IActionResult)await executor.ExecuteAsync(controller, orderedArguments); ???????????????????} ???????????????????else ???????????????????{ ???????????????????????// Sync method returning IActionResult (e.g., ViewResult) ???????????????????????result = (IActionResult)executor.Execute(controller, orderedArguments); ???????????????????} ???????????????????if (result == null) ???????????????????{ ???????????????????????throw new InvalidOperationException( ???????????????????????????Resources.FormatActionResult_ActionReturnValueCannotBeNull(executor.AsyncResultType ?? returnType)); ???????????????????} ???????????????} ???????????????else if (!executor.IsMethodAsync) ???????????????{ ???????????????????// Sync method returning arbitrary object ???????????????????var resultAsObject = executor.Execute(controller, orderedArguments); ???????????????????result = resultAsObject as IActionResult ?? new ObjectResult(resultAsObject) ???????????????????{ ???????????????????????DeclaredType = returnType, ???????????????????}; ???????????????} ???????????????else if (executor.AsyncResultType == typeof(void)) ???????????????{ ???????????????????// Async method returning awaitable-of-void ???????????????????await executor.ExecuteAsync(controller, orderedArguments); ???????????????????result = new EmptyResult(); ???????????????} ???????????????else ???????????????{ ???????????????????// Async method returning awaitable-of-nonvoid ???????????????????var resultAsObject = await executor.ExecuteAsync(controller, orderedArguments); ???????????????????result = resultAsObject as IActionResult ?? new ObjectResult(resultAsObject) ???????????????????{ ???????????????????????DeclaredType = executor.AsyncResultType, ???????????????????}; ???????????????} ???????????????_result = result; ???????????????logger.ActionMethodExecuted(controllerContext, result); ???????????} ???????????finally ???????????{ ???????????????diagnosticSource.AfterActionMethod( ???????????????????controllerContext, ???????????????????arguments, ???????????????????controllerContext, ???????????????????result); ???????????} ???????}上面的方法在于不断判断returnType的类型，根据不同的类型执行不同的操作。不难发现，这些returnType正是我们所写的Action的返回类型。换句话说，executor.Execute执行的正是我们的Action方法。那么，executor又是什么呢？它是一个ObjectMethodExecutor类型的变量。从它构造函数可以看出，它实质上是对一个方法的包装。
private ObjectMethodExecutor(MethodInfo methodInfo, TypeInfo targetTypeInfo, object[] parameterDefaultValues) ???????{ ???????????if (methodInfo == null) ???????????{ ???????????????throw new ArgumentNullException(nameof(methodInfo)); ???????????} ???????????MethodInfo = methodInfo; ???????????MethodParameters = methodInfo.GetParameters(); ???????????TargetTypeInfo = targetTypeInfo; ???????????MethodReturnType = methodInfo.ReturnType; ???????????var isAwaitable = CoercedAwaitableInfo.IsTypeAwaitable(MethodReturnType, out var coercedAwaitableInfo); ???????????IsMethodAsync = isAwaitable; ???????????AsyncResultType = isAwaitable ? coercedAwaitableInfo.AwaitableInfo.ResultType : null; ???????????// Upstream code may prefer to use the sync-executor even for async methods, because if it knows ???????????// that the result is a specific Task<T> where T is known, then it can directly cast to that type ???????????// and await it without the extra heap allocations involved in the _executorAsync code path. ?????????????//看这里 ???????????_executor = GetExecutor(methodInfo, targetTypeInfo); ???????????if (IsMethodAsync) ???????????{ ???????????????_executorAsync = GetExecutorAsync(methodInfo, targetTypeInfo, coercedAwaitableInfo); ???????????} ???????????_parameterDefaultValues = parameterDefaultValues; ???????}public object Execute(object target, object[] parameters) ???????{ ???????????return _executor(target, parameters); ???????} Execute方法也只是委托_executor去执行了。而_executor又是在构造函数中赋值的，下面是GetExecutor方法。
private static MethodExecutor GetExecutor(MethodInfo methodInfo, TypeInfo targetTypeInfo) ???????{ ???????????// Parameters to executor ???????????var targetParameter = Expression.Parameter(typeof(object), "target"); ???????????var parametersParameter = Expression.Parameter(typeof(object[]), "parameters"); ???????????// Build parameter list ???????????var parameters = new List<Expression>(); ???????????var paramInfos = methodInfo.GetParameters(); ???????????for (int i = 0; i < paramInfos.Length; i++) ???????????{ ???????????????var paramInfo = paramInfos[i]; ???????????????var valueObj = Expression.ArrayIndex(parametersParameter, Expression.Constant(i)); ???????????????var valueCast = Expression.Convert(valueObj, paramInfo.ParameterType); ???????????????// valueCast is "(Ti) parameters[i]" ???????????????parameters.Add(valueCast); ???????????} ???????????// Call method ???????????var instanceCast = Expression.Convert(targetParameter, targetTypeInfo.AsType()); ???????????var methodCall = Expression.Call(instanceCast, methodInfo, parameters); ???????????// methodCall is "((Ttarget) target) method((T0) parameters[0], (T1) parameters[1], ...)" ???????????// Create function ???????????if (methodCall.Type == typeof(void)) ???????????{ ???????????????var lambda = Expression.Lambda<VoidMethodExecutor>(methodCall, targetParameter, parametersParameter); ???????????????var voidExecutor = lambda.Compile(); ???????????????return WrapVoidMethod(voidExecutor); ???????????} ???????????else ???????????{ ???????????????// must coerce methodCall to match ActionExecutor signature ???????????????var castMethodCall = Expression.Convert(methodCall, typeof(object)); ???????????????var lambda = Expression.Lambda<MethodExecutor>(castMethodCall, targetParameter, parametersParameter); ???????????????return lambda.Compile(); ???????????} ???????}可以看到，上面利用表达式类编译成了委托，并且区分有无返回值的情况。至此，我们已经过了整个MVC框架的流程。现在，让我们再重新梳理一遍。
? Internet=>Application=>Middleware=>IRourer=>MvcRouterHandler=>ControllerActionInvoker=》ActionFilter
? 网络和应用程序之间，通过HTTP协议交互信息。而在应用程序内部，又有由一系列中间件编译成的委托链。然后是整个MVC的入口点，即路由中间件。其中使用了IRouter的RouteAsync方法匹配路由。而在IRouter的默认实现MvcRouterHandler中又调用了IActionInvoker的InvokeAsync方法。IActionInvoker的默认实现ControllerActionInvoker又继承了ResourceInvoker。在ResourceInvoker中，执行了整个过滤器管道的流程。而动作过滤器和真正的动作方法则是在ControllerActionInvoker中执行的。
ASP.NET Core学习总结(3)
原文地址：https://www.cnblogs.com/xsddxz/p/9059736.html