c# - 导出“XYZ.IMessageCenterBL(ContractName =“XYZ.IMessageCenterBL”)”不可分配为类型“System.Web.Mvc.JsonResult”

与出口问题不是特定类型的其他问题不同，这一问题是完全不同的。

类型XYZ.IMessageCenterBL和System.Web.Mvc.JsonResult完全不同-我们无法混淆它们。

而且，如果我尝试使用System.Web.Mvc.JsonResult而不是XYZ.IMessageCenterBL，则代码将无法编译。

现在，将XYZ.IMessageCenterBL注入到属性中：

[Import]
public IMessageCenterBL MessageCenterBL { get; set; }

请注意，没有任何混乱的地方-此JsonResult业务来自何处？

另外，如果我将依赖项从属性移到构造函数中（即IMessageCenterBL被注入到构造函数中，并且从那里显式设置了属性），它将开始起作用！

这是整个MEF异常输出：

Unhandled Exception at url: http://localhost:51000/u/2s4xYN1VikulrQAi44nvWg/Framework/XmlForm/GetTemplate
System.InvalidOperationException: An error occurred when trying to create a controller of type 'DF.Web.Framework.Controllers.XmlForms.XmlFormController`1[DF.Data.WorkFlow.WF_Employee]'. Make sure that the controller has a parameterless public constructor. ---> System.ComponentModel.Composition.CompositionException: The composition produced a single composition error. The root cause is provided below. Review the CompositionException.Errors property for more detailed information.

1) The export 'DF.Web.Framework.Business.IMessageCenterBL (ContractName="DF.Web.Framework.Business.IMessageCenterBL")' is not assignable to type 'System.Web.Mvc.JsonResult'.

Resulting in: Cannot set import 'DF.Web.Platform.DFController.Data (ContractName="DF.Web.Framework.Business.IMessageCenterBL")' on part 'DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee)'.
Element: DF.Web.Platform.DFController.Data (ContractName="DF.Web.Framework.Business.IMessageCenterBL") -->  DF.Web.Framework.Controllers.XmlForms.XmlFormController({0}) -->  AssemblyCatalog (Assembly="DF.Web.Framework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b3dac0a0872f0a93")

Resulting in: Cannot get export 'DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee) (ContractName="DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee)")' from part 'DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee)'.
Element: DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee) (ContractName="DF.Web.Framework.Controllers.XmlForms.XmlFormController(DF.Data.WorkFlow.WF_Employee)") -->  DF.Web.Framework.Controllers.XmlForms.XmlFormController({0}) -->  AssemblyCatalog (Assembly="DF.Web.Framework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b3dac0a0872f0a93")

   at System.ComponentModel.Composition.Hosting.CompositionServices.GetExportedValueFromComposedPart(ImportEngine engine, ComposablePart part, ExportDefinition definition)
   at System.ComponentModel.Composition.Hosting.CatalogExportProvider.GetExportedValue(CatalogPart part, ExportDefinition export, Boolean isSharedPart)
   at System.ComponentModel.Composition.Hosting.CatalogExportProvider.CatalogExport.GetExportedValueCore()
   at System.ComponentModel.Composition.Primitives.Export.get_Value()
   at System.ComponentModel.Composition.ExportServices.GetCastedExportedValue[T](Export export)
   at System.ComponentModel.Composition.ReflectionModel.ExportFactoryCreator.LifetimeContext.GetExportLifetimeContextFromExport[T](Export export)
   at System.ComponentModel.Composition.ReflectionModel.ExportFactoryCreator.<>c__DisplayClass4`1.<CreateStronglyTypedExportFactoryOfT>b__3()
   at System.ComponentModel.Composition.ExportFactory`1.CreateExport()
   at DF.Web.Platform.MefDependencyResolver.CacheItem`1.GetService(CompositionContainer compositionContainer) in c:\DF\SharpTop\UI\Platform\MefDependencyResolver.cs:line 41
   at DF.Web.Platform.MefDependencyResolver.System.Web.Mvc.IDependencyResolver.GetService(Type serviceType) in c:\DF\SharpTop\UI\Platform\MefDependencyResolver.cs:line 100
   at System.Web.Mvc.DefaultControllerFactory.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType)
   --- End of inner exception stack trace ---
   at System.Web.Mvc.DefaultControllerFactory.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType)
   at System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType)
   at System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName)
   at System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory)
   at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state)
   at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state)
   at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

MEF如何混淆这两种类型？

最佳答案

我现在重新测试了整个问题，一切正常。知道它是由两个独立的开发人员在两台计算机上复制的，所以我无法解释这种奇怪的行为...

关于c# - 导出“XYZ.IMessageCenterBL(ContractName =“XYZ.IMessageCenterBL”)”不可分配为类型“System.Web.Mvc.JsonResult”，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/31329914/