看mvc的源码我们知道，它是在 ControllerActionInvoker 类中执行 InvokeAction 方法来实现过滤器和action方法执行的。 

通过查看源码我们知道，他是通过调用 InvokeActionMethodWithFilters 方法来实现IActionFilter过滤器和action方法执行的，如图 

点进去这个方法我们可以看到 

protected virtual ActionExecutedContext InvokeActionMethodWithFilters(ControllerContext controllerContext, IList<IActionFilter> filters, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters)
{
    ActionExecutingContext preContext = new ActionExecutingContext(controllerContext, actionDescriptor, parameters);
    Func<ActionExecutedContext> seed = () => new ActionExecutedContext(controllerContext, actionDescriptor, false, null)
    {
        Result = this.InvokeActionMethod(controllerContext, actionDescriptor, parameters)
    };
    return filters.Reverse<IActionFilter>().Aggregate(seed, (Func<ActionExecutedContext> next, IActionFilter filter) => () => ControllerActionInvoker.InvokeActionMethodFilter(filter, preContext, next))();
}

看到这里我直接懵逼了，由于它委托中嵌套了委托而且还简写，还调用了扩展方法Aggregate累加器，所以很难直接看懂，这到底是怎么执行代码的呐？我来把代码整理如下 

   public class Class1
    {

        protected virtual ActionExecutedContext InvokeActionMethodWithFilters(ControllerContext controllerContext, IList<IActionFilter> filters, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters)
        {
            ActionExecutingContext preContext = new ActionExecutingContext(controllerContext, actionDescriptor, parameters);

            Func<ActionExecutedContext> seed = () => new ActionExecutedContext(controllerContext, actionDescriptor, false, null)
            {
                Result = this.InvokeActionMethod(controllerContext, actionDescriptor, parameters)
            };

            Func<Func<ActionExecutedContext>, IActionFilter, Func<ActionExecutedContext>> secondParam =
                (Func<ActionExecutedContext> next, IActionFilter filter) =>
                {
                    Func<ActionExecutedContext> returnFunc = () =>
                    {
                        return Class1.InvokeActionMethodFilter(filter, preContext, next);
                    };

                    return returnFunc;

                    //这个是简写
                    //return () => Class1.InvokeActionMethodFilter(filter, preContext, next);                    
                };

            return filters.Reverse<IActionFilter>().Aggregate(seed,
                //(Func<ActionExecutedContext> next, IActionFilter filter) => () => Class1.InvokeActionMethodFilter(filter, preContext, next)
                secondParam
                )
                .Invoke();
        }

        internal static ActionExecutedContext InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func<ActionExecutedContext> continuation)
        {
            filter.OnActionExecuting(preContext);
            if (preContext.Result != null)
            {
                return new ActionExecutedContext(preContext, preContext.ActionDescriptor, true, null)
                {
                    Result = preContext.Result
                };
            }
            bool flag = false;
            ActionExecutedContext actionExecutedContext = null;
            try
            {
                actionExecutedContext = continuation();
            }
            catch (ThreadAbortException)
            {
                actionExecutedContext = new ActionExecutedContext(preContext, preContext.ActionDescriptor, false, null);
                filter.OnActionExecuted(