asp.net-mvc - DefaultControllerFactory 的 GetControllerInstance 方法中的 RequestContext 参数是干什么用的？

Question

我偶然发现了这种方法

protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType)
    {
        if (controllerType == null)
        {
            throw new HttpException(404,
                                    String.Format(
                                        CultureInfo.CurrentCulture,
                                        MvcResources.DefaultControllerFactory_NoControllerFound,
                                        requestContext.HttpContext.Request.Path));
        }
        if (!typeof(IController).IsAssignableFrom(controllerType))
        {
            throw new ArgumentException(
                String.Format(
                    CultureInfo.CurrentCulture,
                    MvcResources.DefaultControllerFactory_TypeDoesNotSubclassControllerBase,
                    controllerType),
                "controllerType");
        }
        return ControllerActivator.Create(requestContext, controllerType);
    }

我想知道 requestContext 参数的用途是什么，因为它似乎从未使用过。它被传递给 ControllerActivator.Create 但它也从未真正在那里使用过：

public IController Create(RequestContext requestContext, Type controllerType)
        {
            try
            {
                return (IController)(_resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType));
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.DefaultControllerFactory_ErrorCreatingController,
                        controllerType),
                    ex);
            }
        }

Answer 1

的目的是按需ControllerFactory创建实例。Controller为了能够确定适当的Controller类型，它可能需要 RequestContext 数据。

现在，DefaultControllerFactory（这是默认工厂）确实使用RequestContextonly 来抛出Http 404 Not Found异常（在需要时），但其他控制器工厂（必须实现IControllerFactory）可能会使用它。

例如，UnityControllerFactory（来源）：

public class UnityControllerFactory : DefaultControllerFactory
    {
        public override IController CreateController(RequestContext context, string controllerName)
        {
            Type type = GetControllerType(context, controllerName);

            if (type == null)
            {
                throw new InvalidOperationException(string.Format("Could not find a controller with the name {0}", controllerName));
            }

            IUnityContainer container = GetContainer(context);
            return (IController)container.Resolve(type);
        }

        protected virtual IUnityContainer GetContainer(RequestContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException("context");
            }

            var unityContainerAccessor = context.HttpContext.ApplicationInstance as IUnityContainerAccessor;
            if (unityContainerAccessor == null)
            {
                throw new InvalidOperationException(
                    "You must extend the HttpApplication in your web project and implement the IContainerAccessor to properly expose your container instance");
            }

            IUnityContainer container = unityContainerAccessor.Container;
            if (container == null)
            {
                throw new InvalidOperationException("The container seems to be unavailable in your HttpApplication subclass");
            }

            return container;
        }