C# 两次导入类型会导致MEF失败

我试图用MEF编写一个小模块系统，因此我有一个基本模块，如下所示：

public abstract class Module : IModule
{
    [Import]
    private IShell _shell;

    protected IShell Shell
    {
        get { return _shell; }
    }
}

还有一些类似的模块：

[Export(typeof(IModule))]
public class TodoListModule : Module
{

}

如您所见，基本模块依赖于IShell。我有一个这样的实现：

[Export(typeof(IShell))]
public class ShellViewModel : IShell
{
    [ImportMany]
    private IEnumerable<IModule> _modules;

    .... and later...

    private void InitializeModules()
    {
        foreach (var module in _modules)
        {
            // init modules.
        }
    }
}

因此，原因是我们有两个实现通过基类获得IShell。为什么会这样

这是我的容器配置：

        // Add all assemblies to AssemblySource (using a temporary DirectoryCatalog).
        var directoryCatalog = new DirectoryCatalog(@"./");
        AssemblySource.Instance.AddRange(
            directoryCatalog.Parts
                .Select(part => ReflectionModelServices.GetPartType(part).Value.Assembly)
                .Where(assembly => !AssemblySource.Instance.Contains(assembly)));

        // Prioritise the executable assembly. This allows the client project to override exports, including IShell.
        // The client project can override SelectAssemblies to choose which assemblies are prioritised.
        var priorityAssemblies = SelectAssemblies().ToList();
        var priorityCatalog = new AggregateCatalog(priorityAssemblies.Select(x => new AssemblyCatalog(x)));
        var priorityProvider = new CatalogExportProvider(priorityCatalog);

        // Now get all other assemblies (excluding the priority assemblies).
        var mainCatalog = new AggregateCatalog(
            AssemblySource.Instance
                .Where(assembly => !priorityAssemblies.Contains(assembly))
                .Select(x => new AssemblyCatalog(x)));
        var mainProvider = new CatalogExportProvider(mainCatalog);

        container = new CompositionContainer(priorityProvider, mainProvider);
        priorityProvider.SourceProvider = container;
        mainProvider.SourceProvider = container;

        var batch = new CompositionBatch();

        BindServices(batch);
        batch.AddExportedValue(mainCatalog);

        container.Compose(batch);

---

当任何其他类导入IShell时也会发生这种情况

为什么需要编写？当您处理尝试引用模块的未知对象时，此功能非常好。也许这能帮你。在这里，我描述了批量导入是如何工作的，您可以下载一个能够编写的工作解决方案，IShell是否可能从IModule中导入？如果是这样的话，您可能会在尝试撰写时陷入循环依赖，因为ShellViewModel@JPVensonIShell不继承IModule。配置代码是我为Caliburn.Micro找到的一些引导代码的一部分。我已经有了一个可行的解决方案，但我无法找出有什么不同的做法，因为配置代码就在那里。

        // Add all assemblies to AssemblySource (using a temporary DirectoryCatalog).
        var directoryCatalog = new DirectoryCatalog(@"./");
        AssemblySource.Instance.AddRange(
            directoryCatalog.Parts
                .Select(part => ReflectionModelServices.GetPartType(part).Value.Assembly)
                .Where(assembly => !AssemblySource.Instance.Contains(assembly)));

        // Prioritise the executable assembly. This allows the client project to override exports, including IShell.
        // The client project can override SelectAssemblies to choose which assemblies are prioritised.
        var priorityAssemblies = SelectAssemblies().ToList();
        var priorityCatalog = new AggregateCatalog(priorityAssemblies.Select(x => new AssemblyCatalog(x)));
        var priorityProvider = new CatalogExportProvider(priorityCatalog);

        // Now get all other assemblies (excluding the priority assemblies).
        var mainCatalog = new AggregateCatalog(
            AssemblySource.Instance
                .Where(assembly => !priorityAssemblies.Contains(assembly))
                .Select(x => new AssemblyCatalog(x)));
        var mainProvider = new CatalogExportProvider(mainCatalog);

        container = new CompositionContainer(priorityProvider, mainProvider);
        priorityProvider.SourceProvider = container;
        mainProvider.SourceProvider = container;

        var batch = new CompositionBatch();

        BindServices(batch);
        batch.AddExportedValue(mainCatalog);

        container.Compose(batch);