.NET Core开发日志—

在叙述Controller一文中，有一处未做解释，即CreateControllerFactory方法中ControllerActionDescriptor参数是如何产生的。这是因为其与Action的关联性更大，所以放在本文中继续描述。

回到MvcRouteHandler或者MvcAttributeRouteHandler的方法中：

public Task RouteAsync(RouteContext context)

{

    ...

    var candidates = _actionSelector.SelectCandidates(context);

    if (candidates == null || candidates.Count == 0)

    {

        _logger.NoActionsMatched(context.RouteData.Values);

        return Task.CompletedTask;

    }

    var actionDescriptor = _actionSelector.SelectBestCandidate(context, candidates);

    if (actionDescriptor == null)

    {

        _logger.NoActionsMatched(context.RouteData.Values);

        return Task.CompletedTask;

    }

    context.Handler = (c) =>

    {

        var routeData = c.GetRouteData();

        var actionContext = new ActionContext(context.HttpContext, routeData, actionDescriptor);

        if (_actionContextAccessor != null)

        {

            _actionContextAccessor.ActionContext = actionContext;

        }

        var invoker = _actionInvokerFactory.CreateInvoker(actionContext);

        if (invoker == null)

        {

            throw new InvalidOperationException(

                Resources.FormatActionInvokerFactory_CouldNotCreateInvoker(

                    actionDescriptor.DisplayName));

        }

        return invoker.InvokeAsync();

    };

    ...

}

不难发现作为源头的ActionContext中传入了actionDescriptor，而这个参数的值是在ActionSelector中被筛选出来的。

public IReadOnlyList<ActionDescriptor> SelectCandidates(RouteContext context)

{

    ...

    var cache = Current;

    // The Cache works based on a string[] of the route values in a pre-calculated order. This code extracts

    // those values in the correct order.

    var keys = cache.RouteKeys;

    var values = new string[keys.Length];

    for (var i = 0; i < keys.Length; i++)

    {

        context.RouteData.Values.TryGetValue(keys[i], out object value);

        if (value != null)

        {

            values[i] = value as string ?? Convert.ToString(value);

        }

    }

    if (cache.OrdinalEntries.TryGetValue(values, out var matchingRouteValues) ||

        cache.OrdinalIgnoreCaseEntries.TryGetValue(values, out matchingRouteValues))

    {

        Debug.Assert(matchingRouteValues != null);

        return matchingRouteValues;

    }

    _logger.NoActionsMatched(context.RouteData.Values);

    return EmptyActions;

}

然后可供筛选的ActionDescriptors集合又是来自ActionDescriptorCollectionProvider类。

private Cache Current

{

    get

    {

        var actions = _actionDescriptorCollectionProvider.ActionDescriptors;

        var cache = Volatile.Read(ref _cache);

        if (cache != null && cache.Version == actions.Version)

        {

            return cache;

        }

        cache = new Cache(actions);

        Volatile.Write(ref _cache, cache);

        return cache;

    }

}

它的内部又再调用了ControllerActionDescriptorProvider类的OnProvidersExecuting方法。

public ActionDescriptorCollection ActionDescriptors

{

    get

    {

        if (_collection == null)

        {

            UpdateCollection();

        }

        return _collection;

    }

}

private void UpdateCollection()

{

    var context = new ActionDescriptorProviderContext();

    for (var i = 0; i < _actionDescriptorProviders.Length; i++)

    {

        _actionDescriptorProviders[i].OnProvidersExecuting(context);

    }

    for (var i = _actionDescriptorProviders.Length - 1; i >= 0; i--)

    {

        _actionDescriptorProviders[i].OnProvidersExecuted(context);

    }

    _collection = new ActionDescriptorCollection(

        new ReadOnlyCollection<ActionDescriptor>(context.Results),

        Interlocked.Increment(ref _version));

}

调用链继续深入到DefaultApplicationModelProvider之中。

public void OnProvidersExecuting(ActionDescriptorProviderContext context)

{

    if (context == null)

    {

        throw new ArgumentNullException(nameof(context));

    }

    foreach (var descriptor in GetDescriptors())

    {

        context.Results.Add(descriptor);

    }

}

protected internal IEnumerable<ControllerActionDescriptor> GetDescriptors()

{

    var applicationModel = BuildModel();

    ApplicationModelConventions.ApplyConventions(applicationModel, _conventions);

    return ControllerActionDescriptorBuilder.Build(applicationModel);

}

protected internal ApplicationModel BuildModel()

{

    var controllerTypes = GetControllerTypes();

    var context = new ApplicationModelProviderContext(controllerTypes);

    for (var i = 0; i < _applicationModelProviders.Length; i++)

    {

        _applicationModelProviders[i].OnProvidersExecuting(context);

    }

    for (var i = _applicationModelProviders.Length - 1; i >= 0; i--)

    {

        _applicationModelProviders[i].OnProvidersExecuted(context);

    }

    return context.Result;

}

private IEnumerable<TypeInfo> GetControllerTypes()

{

    var feature = new ControllerFeature();

    _partManager.PopulateFeature(feature);

    return feature.Controllers;

}

到了这里终于可以看到Action的影子，虽然现在还只是ActionModel。

public virtual void OnProvidersExecuting(ApplicationModelProviderContext context)

{

    ...

    foreach (var controllerType in context.ControllerTypes)

    {

        var controllerModel = CreateControllerModel(controllerType);

        if (controllerModel == null)

        {

            continue;

        }

        context.Result.Controllers.Add(controllerModel);

        controllerModel.Application = context.Result;

        ...

        foreach (var methodInfo in controllerType.AsType().GetMethods())

        {

            var actionModel = CreateActionModel(controllerType, methodInfo);

            if (actionModel == null)

            {

                continue;

            }

            actionModel.Controller = controllerModel;

            controllerModel.Actions.Add(actionModel);

            foreach (var parameterInfo in actionModel.ActionMethod.GetParameters())

            {

                var parameterModel = CreateParameterModel(parameterInfo);

                if (parameterModel != null)

                {

                    parameterModel.Action = actionModel;

                    actionModel.Parameters.Add(parameterModel);

                }

            }

        }

    }

}

利用ControllerActionDescriptorBuilder类的Build方法，可以得到预期的ControllerActionDescriptor。

public static IList<ControllerActionDescriptor> Build(ApplicationModel application)

{

    var actions = new List<ControllerActionDescriptor>();

    var methodInfoMap = new MethodToActionMap();

    var routeTemplateErrors = new List<string>();

    var attributeRoutingConfigurationErrors = new Dictionary<MethodInfo, string>();

    foreach (var controller in application.Controllers)

    {

        // Only add properties which are explicitly marked to bind.

        // The attribute check is required for ModelBinder attribute.

        var controllerPropertyDescriptors = controller.ControllerProperties

            .Where(p => p.BindingInfo != null)

            .Select(CreateParameterDescriptor)

            .ToList();

        foreach (var action in controller.Actions)

        {

            // Controllers with multiple [Route] attributes (or user defined implementation of

            // IRouteTemplateProvider) will generate one action descriptor per IRouteTemplateProvider

            // instance.

            // Actions with multiple [Http*] attributes or other (IRouteTemplateProvider implementations

            // have already been identified as different actions during action discovery.

            var actionDescriptors = CreateActionDescriptors(application, controller, action);

            foreach (var actionDescriptor in actionDescriptors)

            {

                actionDescriptor.ControllerName = controller.ControllerName;

                actionDescriptor.ControllerTypeInfo = controller.ControllerType;

                AddApiExplorerInfo(actionDescriptor, application, controller, action);

                AddRouteValues(actionDescriptor, controller, action);

                AddProperties(actionDescriptor, action, controller, application);

                actionDescriptor.BoundProperties = controllerPropertyDescriptors;

                if (IsAttributeRoutedAction(actionDescriptor))

                {

                    // Replaces tokens like [controller]/[action] in the route template with the actual values

                    // for this action.

                    ReplaceAttributeRouteTokens(actionDescriptor, routeTemplateErrors);

                }

            }

            methodInfoMap.AddToMethodInfo(action, actionDescriptors);

            actions.AddRange(actionDescriptors);

        }

    }

    ...

    return actions;

}

ControllerActionDescriptor包含了足以构建Controller与Action的属性。

public string ControllerName { get; set; }

public virtual string ActionName { get; set; }

public MethodInfo MethodInfo { get; set; }

public TypeInfo ControllerTypeInfo { get; set; }

public IList<ParameterDescriptor> Parameters { get; set; }

Controller的构建已经介绍过了，现在该谈谈关于Action的。

先找到创建ControllerActionInvokerCacheEntry对象的ControllerActionInvokerCache类的GetCachedResult方法。可以看到两个关键参数objectMethodExecutor与actionMethodExecutor的创建方式。

public (ControllerActionInvokerCacheEntry cacheEntry, IFilterMetadata[] filters) GetCachedResult(ControllerContext controllerContext)

{

    var cache = CurrentCache;

    var actionDescriptor = controllerContext.ActionDescriptor;

    IFilterMetadata[] filters;

    if (!cache.Entries.TryGetValue(actionDescriptor, out var cacheEntry))

    {

        ...

        var objectMethodExecutor = ObjectMethodExecutor.Create(

            actionDescriptor.MethodInfo,

            actionDescriptor.ControllerTypeInfo,

            parameterDefaultValues);

        ...

        var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);

        cacheEntry = new ControllerActionInvokerCacheEntry(

            filterFactoryResult.CacheableFilters,

            controllerFactory,

            controllerReleaser,

            propertyBinderFactory,

            objectMethodExecutor,

            actionMethodExecutor);

        cacheEntry = cache.Entries.GetOrAdd(actionDescriptor, cacheEntry);

    }

    ...

    return (cacheEntry, filters);

}

再到ControllerActionInvoker类的Next方法中跟踪到State.ActionInside环节：

case State.ActionInside:

    {

        var task = InvokeActionMethodAsync();

        if (task.Status != TaskStatus.RanToCompletion)

        {

            next = State.ActionEnd;

            return task;

        }

        goto case State.ActionEnd;

    }

终于可以找到创建Action的方法。

private async Task InvokeActionMethodAsync()

{

    var controllerContext = _controllerContext;

    var objectMethodExecutor = _cacheEntry.ObjectMethodExecutor;

    var controller = _instance;

    var arguments = _arguments;

    var actionMethodExecutor = _cacheEntry.ActionMethodExecutor;

    var orderedArguments = PrepareArguments(arguments, objectMethodExecutor);

    var diagnosticSource = _diagnosticSource;

    var logger = _logger;

    IActionResult result = null;

    try

    {

        diagnosticSource.BeforeActionMethod(

            controllerContext,

            arguments,

            controller);

        logger.ActionMethodExecuting(controllerContext, orderedArguments);

        var stopwatch = ValueStopwatch.StartNew();

        var actionResultValueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, orderedArguments);

        if (actionResultValueTask.IsCompletedSuccessfully)

        {

            result = actionResultValueTask.Result;

        }

        else

        {

            result = await actionResultValueTask;

        }

        _result = result;

        logger.ActionMethodExecuted(controllerContext, result, stopwatch.GetElapsedTime());

    }

    ...

}

核心的代码是这一句actionMethodExecutor.Execute(objectMethodExecutor, controller, orderedArguments)。

actionMethodExecutor与objectMethodExecutor即是之前生成ControllerActionInvokerCacheEntry对象时传入的两个参数，controller是在State.ActionBegin环节通过_instance = _cacheEntry.ControllerFactory(controllerContext);生成的。orderedArguments是Action方法所需的参数。

至于更详细的创建过程，可以到ActionMethodExecutor类与ObjectMethodExecutor类中探寻，主要是涉及反射相关的知识，这里就不做进一步解释了。

巴特西

.NET Core开发日志——Action

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