如何调试MEF异常？

我们目前正在使用 MEF（托管扩展性框架，http://mef.codeplex.com/）并且它会抛出异常，而可供继续处理的信息有限。

有没有办法调试 MEF 异常？

我的例外是这样的：

System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

   at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module)

   at System.Reflection.RuntimeModule.GetTypes()

   at System.Reflection.Assembly.GetTypes()

   at System.ComponentModel.Composition.Hosting.AssemblyCatalog.get_InnerCatalog()

   at System.ComponentModel.Composition.Hosting.AssemblyCatalog.GetExports(ImportDefinition definition)

   at System.ComponentModel.Composition.Hosting.AggregateCatalog.GetExports(ImportDefinition definition)

   at System.ComponentModel.Composition.Hosting.CatalogExportProvider.GetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ExportProvider.TryGetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition, IEnumerable`1& exports)

   at System.ComponentModel.Composition.Hosting.AggregateExportProvider.GetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ExportProvider.TryGetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition, IEnumerable`1& exports)

   at System.ComponentModel.Composition.Hosting.ExportProvider.TryGetExports(ImportDefinition definition, AtomicComposition atomicComposition, IEnumerable`1& exports)

   at System.ComponentModel.Composition.Hosting.CompositionContainer.GetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ExportProvider.TryGetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition, IEnumerable`1& exports)

   at System.ComponentModel.Composition.Hosting.ExportProvider.GetExports(ImportDefinition definition, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ImportEngine.TryGetExports(ExportProvider provider, ComposablePart part, ImportDefinition definition, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ImportEngine.TrySatisfyImportSubset(PartManager partManager, IEnumerable`1 imports, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ImportEngine.TryPreviewImportsStateMachine(PartManager partManager, ComposablePart part, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ImportEngine.PreviewImports(ComposablePart part, AtomicComposition atomicComposition)

   at System.ComponentModel.Composition.Hosting.ComposablePartExportProvider.Compose(CompositionBatch batch)

   at System.ComponentModel.Composition.Hosting.CompositionContainer.Compose(CompositionBatch batch)

   at System.ComponentModel.Composition.AttributedModelServices.ComposeParts(CompositionContainer container, Object[] attributedParts)

   at MyApp.Extension..ctor(Assembly assembly) in W:\MyApp\Source\\Extensions\Extension.cs:line 45

代码很简单：

var aggregateCatalog = new AggregateCatalog();
_assembly = assembly;
var assemblyCatalog = new AssemblyCatalog(assembly);
aggregateCatalog.Catalogs.Add(new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly()));
aggregateCatalog.Catalogs.Add(assemblyCatalog);
_compositionContainer = new CompositionContainer(aggregateCatalog);
_compositionContainer.ComposeParts(this);

I 感受你的痛苦。当我陷入困境时，我通常会转储 MEF 组合信息以获取有关组合失败原因的更多信息。有关如何执行此操作的说明，请参阅诊断构图问题在 MEF 编程指南或调试MEFMSDN 上的主题。

在 .NET 4.5（或 codeplex 上当前可用的 MEF 2 预览版 4 版本）中，有一个更简单的选项：您可以通过在构图选项您将其传递给容器构造函数。

edit: 啊，你得到了ReflectionTypeLoadException。那是另一回事：这意味着某些程序集中的类型无法成功加载，通常是因为它们引用了无法找到的其他类型。在您的代码示例中，您应该能够通过调用来重现问题assembly.GetTypes()，不涉及MEF。