统一ResolutionFailedException用于System.Web.Mvc类型

Question

我的WebApp是WebForms页面和MVC 4页面的组合。

使用联合，我将得到以下异常。

异常类型：

Microsoft.Practices.Unity.ResolutionFailedException, Microsoft.Practices.Unity, Version=2.1.505.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35

消息：

Resolution of the dependency failed, type = "System.Web.Mvc.ModelMetadataProvider", name = "(none)".  Exception occurred while: while resolving.  Exception is: InvalidOperationException - The type ModelMetadataProvider does not have an accessible constructor.  At the time of the exception, the container was:
Resolving System.Web.Mvc.ModelMetadataProvider,(none)

Inner Exception为：

消息：

The type ModelMetadataProvider does not have an accessible constructor.

堆栈跟踪

at Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.ThrowForNullExistingObje ct(IBuilderContext context)  
at BuildUp_System.Web.Mvc.ModelMetadataProvider(IBuilderContext )  
at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)  
at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)  
at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)  
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides)  

对于以下类型，我始终得到相同的解析异常：

System.Web.Mvc.ITempDataProvide  
System.Web.Mvc.Async.IAsyncActionInvoker  
System.Web.Mvc.IActionInvoker  
System.Web.Mvc.ModelMetadataProvider  
System.Web.Mvc.IViewPageActivator

在Application_Start中，我使用以下方法设置IoC：

DependencyResolver.SetResolver(new UnityDependencyResolver(UnityConfigurator.GetContainer()));

...where GetContainer返回所有已注册类型，UnityDependencyResolver is-a IDependencyResolver

有什么原因造成这个问题吗？

谢谢,

--教育

Answer 1

我不确定UnityConfigurator.GetContainer()返回的容器实例的行为如何，但我假设它在需要时试图单独解决ModelMetadataProvider问题。这个ModelMetadataProvider有一些依赖项，您的容器不知道只有初始的MVC解析器才能解决。所谓“初始MVC解析器”，我指的是调用DependencyResolver.Current之前的DependencyResolver.SetResolver(...)结果。因此，您需要在自己的容器上实现一个代理，并使用初始的MVC解析器作为后盾。

代理的实现应该是这样的一个快速示例：

public class MvcDependencyResolver:System.Web.Mvc.IDependencyResolver
{
    private readonly IDependencyResolver _resolver;

    private readonly System.Web.Mvc.IDependencyResolver _fallbackResolver;

    public MvcDependencyResolver(IDependencyResolver resolver, System.Web.Mvc.IDependencyResolver fallbackResolver)
    {
        this._resolver = resolver;
        this._fallbackResolver = fallbackResolver;
    }

    public object GetService(Type serviceType)
    {
        if ((this._resolver.IsRegistered(serviceType)) || (serviceType.IsClass))
        {
            try
            {
                return this._resolver.GetService(serviceType);
            }
            catch (ResolutionFailedException)
            {
            }
        }
        return this._fallbackResolver.GetService(serviceType);
    }

然后，在Application_Start()中，用代理的实例覆盖MVC解析器，如下所示：

var bootstrapper = new Bootstrapper();
var resolver = bootstrapper.Run();
DependencyResolver.SetResolver(new MvcDependencyResolver(resolver, DependencyResolver.Current));