如何调试MEF异常？

Question

我们目前使用的是MEF (托管扩展框架，http://mef.codeplex.com/ )，它抛出了异常，但信息有限。

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);

Answer 1

I feel your pain。当我被卡住时，我通常会转储MEF合成信息，以获得有关合成失败原因的更多信息。有关如何执行此操作的说明，请参阅MEF编程指南中的Diagnosing Composition Problems或MSDN上的Debugging MEF主题。

在Codeplex4.5(或目前在.NET上可用的MEF2预览版4版本)中，有一个更简单的选项:您可以通过在传递给容器构造函数的CompositionOptions中禁用静默拒绝来提高错误消息的有用性。

编辑：啊，你得到了一个ReflectionTypeLoadException。这是另一个问题: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assembly.GetTypes()重现问题，而不涉及MEF。

Answer 2

Daniel Plaisted写了一篇相当深入的关于诊断MEF问题的blog article。

你能告诉我们抛出了什么异常吗？