Autofac MEF集成中的错误：仅在查询元数据时实例化组件

Question

在与MEF集成时，Autofac如何处理服务实例化似乎存在错误

以下测试表明MEF在必须之前不会实例化服务。 （在这种情况下，我只是查询元数据）

[TestMethod]
public void Mef_DoesNotInstantiateService_WhenOnlyQueryingForMetadata()
{
    var aggregateCatalog = CreateMefCatalog();
    var container = new CompositionContainer(aggregateCatalog, true);

    var serviceConsumer = container.GetExportedValue<ServiceConsumer>();

    serviceConsumer.Services.Any(x => x.Metadata.Name == "Service1").Should().BeTrue();
}

以下测试失败，因为Autfac正在尝试创建Service1的实例 - 它在构造函数中抛出异常。

[TestMethod]
public void Autofac_DoesNotInstantiateService_WhenOnlyQueryingForMetadata()
{
    var aggregateCatalog = CreateMefCatalog();

    var builder = new ContainerBuilder();
    builder.RegisterComposablePartCatalog(aggregateCatalog);
    var container = builder.Build();

    //Next line will throw an exception. (Autofac is instantiating the service, but should not)
    var serviceConsumer = container.Resolve<ServiceConsumer>();

    //Note: This test will never get here..
    serviceConsumer.Services.Any(x => x.Metadata.Name == "Service1").Should().BeTrue();
}

测试所需的其他代码

static AggregateCatalog CreateMefCatalog()
{
    return new AggregateCatalog(new List<ComposablePartCatalog>
    {
        new AssemblyCatalog(Assembly.GetExecutingAssembly())
    });
}

[Export]
class ServiceConsumer
{
    [ImportMany]
    public IEnumerable<Lazy<IService, INameMetadata>> Services { get; set; }
}


public interface IService { }

[Export(typeof (IService))]
[ExportMetadata("Name", "Service1")]
public class Service1 : IService
{
    public Service1()
    {
        throw new Exception("This service should never be created");
    }
}

public interface INameMetadata
{
    string Name { get; }
}

BTW：我使用的是目前稳定版本：Autofac 3.5.2和Autofac.Mef 3.0.3