.NET Core开发日志—

在理清路由的工作流程后，接下来需要考虑的，是MVC框架如何生成Controller以及它的生成时机。

根据以前ASP.NET MVC的经验，Controller应该是由一个ControllerFactory构建的。查看ASP.NET Core MVC的源码，果然是有一个DefaultControllerFactory类，并且不出意外的，它拥有一个CreateController方法。

public virtual object CreateController(ControllerContext context)

{

    ...

    var controller = _controllerActivator.Create(context);

    foreach (var propertyActivator in _propertyActivators)

    {

        propertyActivator.Activate(context, controller);

    }

    return controller;

}

但细推其使用的场合，只出现在ControllerFactoryProvider的构造方法内部，且仅是用于判断所传入的controllerFactory类型是否是DefaultControllerFactory。

public ControllerFactoryProvider(

    IControllerActivatorProvider activatorProvider,

    IControllerFactory controllerFactory,

    IEnumerable<IControllerPropertyActivator> propertyActivators)

{

    ...

    _activatorProvider = activatorProvider;

    // Compat: Delegate to the IControllerFactory if it's not the default implementation.

    if (controllerFactory.GetType() != typeof(DefaultControllerFactory))

    {

        _factoryCreateController = controllerFactory.CreateController;

        _factoryReleaseController = controllerFactory.ReleaseController;

    }

    _propertyActivators = propertyActivators.ToArray();

}

再看ControllerFactoryProvider内部的CreateControllerFactory方法。这更像是一个真正创建Controller的工厂方法。

public Func<ControllerContext, object> CreateControllerFactory(ControllerActionDescriptor descriptor)

{

    ...

    if (_factoryCreateController != null)

    {

        return _factoryCreateController;

    }

    var controllerActivator = _activatorProvider.CreateActivator(descriptor);

    var propertyActivators = GetPropertiesToActivate(descriptor);

    object CreateController(ControllerContext controllerContext)

    {

        var controller = controllerActivator(controllerContext);

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

        {

            var propertyActivator = propertyActivators[i];

            propertyActivator(controllerContext, controller);

        }

        return controller;

    }

    return CreateController;

}

创建方式分为两种，一种是使用自定义的工厂方法，另一种是通过ControllerActivatorProvider的CreateActivator方法。

public Func<ControllerContext, object> CreateActivator(ControllerActionDescriptor descriptor)

{

    ...

    var controllerType = descriptor.ControllerTypeInfo?.AsType();

    ...

    if (_controllerActivatorCreate != null)

    {

        return _controllerActivatorCreate;

    }

    var typeActivator = ActivatorUtilities.CreateFactory(controllerType, Type.EmptyTypes);

    return controllerContext => typeActivator(controllerContext.HttpContext.RequestServices, arguments: null);

}

明白了如何创建Controller，下面开始调查创建Controller的时机。

ControllerFactoryProvider类的CreateControllerFactory方法是被ControllerActionInvokerCache类的GetCachedResult方法调用。

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 filterFactoryResult = FilterFactory.GetAllFilters(_filterProviders, controllerContext);

        filters = filterFactoryResult.Filters;

        var parameterDefaultValues = ParameterDefaultValues

            .GetParameterDefaultValues(actionDescriptor.MethodInfo);

        var objectMethodExecutor = ObjectMethodExecutor.Create(

            actionDescriptor.MethodInfo,

            actionDescriptor.ControllerTypeInfo,

            parameterDefaultValues);

        var controllerFactory = _controllerFactoryProvider.CreateControllerFactory(actionDescriptor);

        var controllerReleaser = _controllerFactoryProvider.CreateControllerReleaser(actionDescriptor);

        var propertyBinderFactory = ControllerBinderDelegateProvider.CreateBinderDelegate(

            _parameterBinder,

            _modelBinderFactory,

            _modelMetadataProvider,

            actionDescriptor);

        var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);

        cacheEntry = new ControllerActionInvokerCacheEntry(

            filterFactoryResult.CacheableFilters,

            controllerFactory,

            controllerReleaser,

            propertyBinderFactory,

            objectMethodExecutor,

            actionMethodExecutor);

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

    }

    else

    {

        // Filter instances from statically defined filter descriptors + from filter providers

        filters = FilterFactory.CreateUncachedFilters(_filterProviders, controllerContext, cacheEntry.CachedFilters);

    }

    return (cacheEntry, filters);

}

其值作为ControllerActionInvokerCacheEntry对象的一部分被方法返回。

GetCachedResult方法的上层调用者是ControllerActionInvokerProvider类的OnProvidersExecuting方法。

public void OnProvidersExecuting(ActionInvokerProviderContext context)

{

    ...

    if (context.ActionContext.ActionDescriptor is ControllerActionDescriptor)

    {

        var controllerContext = new ControllerContext(context.ActionContext);

        // PERF: These are rarely going to be changed, so let's go copy-on-write.

        controllerContext.ValueProviderFactories = new CopyOnWriteList<IValueProviderFactory>(_valueProviderFactories);

        controllerContext.ModelState.MaxAllowedErrors = _maxModelValidationErrors;

        var cacheResult = _controllerActionInvokerCache.GetCachedResult(controllerContext);

        var invoker = new ControllerActionInvoker(

            _logger,

            _diagnosticSource,

            controllerContext,

            cacheResult.cacheEntry,

            cacheResult.filters);

        context.Result = invoker;

    }

}

ControllerActionInvokerCacheEntry对象又被作为ControllerActionInvoker对象的一部分为ActionInvokerProviderContext的Result属性赋值。

再往上跟踪，到了ActionInvokerFactory类的CreateInvoker方法。

public IActionInvoker CreateInvoker(ActionContext actionContext)

{

    var context = new ActionInvokerProviderContext(actionContext);

    foreach (var provider in _actionInvokerProviders)

    {

        provider.OnProvidersExecuting(context);

    }

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

    {

        _actionInvokerProviders[i].OnProvidersExecuted(context);

    }

    return context.Result;

}

而它的调用者便是MvcRouteHandler或者MvcAttributeRouteHandler。

public Task RouteAsync(RouteContext context)

{

    ...

    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();

    };

    ...

}

到了这里创建Controller的工厂方法还没有被实际调用，此时Controller还是不存在的。所以还需要完成执行ControllerActionInvoker的InvokeAsync方法，或者更准确地说是其基类ResourceInvoker的InvokeAsync方法。

public virtual async Task InvokeAsync()

{

    try

    {

        ...

        using (_logger.ActionScope(_actionContext.ActionDescriptor))

        {

            ...

            try

            {

                await InvokeFilterPipelineAsync();

            }

            ...

        }

    }

    ...

}

从InvokeFilterPipelineAsync方法开始，一系列的处理流程将依据不同状态逐步展开。

private async Task InvokeFilterPipelineAsync()

{

    var next = State.InvokeBegin;

    var scope = Scope.Invoker;

    var state = (object)null;

    var isCompleted = false;

    while (!isCompleted)

    {

        await Next(ref next, ref scope, ref state, ref isCompleted);

    }

}

而到了State.ActionBegin这一步(ControllerActionInvoker类的Next方法)，终于能找到Controller工厂方法被执行的场合。

private Task Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted)

{

    switch (next)

    {

        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;

            }

        ...

        }

    }

}

最后以一张流程图总结上面的探寻过程。

巴特西

.NET Core开发日志——Controller

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