System.Web.Mvc 類型的Unity ResolutionFailedException

Question

我的 WebApp 是 WebForms 頁面和 MVC 4 頁面的組合。

使用 Unity，我收到以下異常。

異常類型：

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

留言：

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 ：

留言：

The type ModelMetadataProvider does not have an accessible constructor.

堆棧跟蹤：

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)  

對於以下類型，我始終得到相同的解析異常：

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，我正在設置 IoC：

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

...其中GetContainer返回所有已注冊的類型，而UnityDependencyResolver是一個IDependencyResolver

任何想法是什么導致了這個問題？

謝謝，
——埃德

Answer 1

我不確定UnityConfigurator.GetContainer()返回的容器實例的行為如何，但我認為它ModelMetadataProvider在需要時嘗試單獨解析ModelMetadataProvider 。 這個ModelMetadataProvider有一些你的容器不知道的依賴項，只有初始 MVC 解析器可以解析。 通過“初始MVC解析器”我的意思的結果DependencyResolver.Current打電話之前DependencyResolver.SetResolver(...) 因此，您需要在自己的容器上實現代理，並將初始 MVC 解析器用作后備。

代理的實現方式的快速示例：

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()您使用此代理的實例覆蓋 MVC 解析器，如下所示：

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