c# - MEF ImportingConstructor ImportMany 与元数据

Question

我正在使用 MEF 在构造函数中导入许多(带有元数据)。我已经按照视频教程尝试模仿它，但到目前为止它还不太奏效。简而言之，我重新命名了一些东西并进行了总结，但是:

AbstractImportMe.cs

[InheritedExport(typeof(AbstractImportMe))]
public abstract class AbstractImportMe{

}

ImportMe.cs

[SimpleMetadata("Name")]
class ImportMe : AbstractImportMe
{

}

SimpleMetadata.cs

[MetadataAttribute]
public class SimpleMetadata : Attribute,ISimpleMetadata
{
    public string Name { get; private set; }
    public SimpleMetadata(String Name)
    {
        this.Name = Name;
    }
}

ISimpleMetadata.cs

public interface ISimpleMetadata
{
    string Name { get; }
}

目录.cs

[Export]
public class Catalog
{

    public IEnumerable<Lazy<AbstractImportMe, ISimpleMetadata>> imports = null;

    [ImportingConstructor]
    /*this runs but the imports field has 0 parts*/
    public Catalog([ImportMany] IEnumerable<Lazy<AbstractImportMe, ISimpleMetadata>> imports)
    {
        this.imports = imports;
    }

    /* this code works, but it lacks metadata
    public IEnumerable<AbstractImportMe> imports= null;

    [ImportingConstructor]
    public Catalog([ImportMany] IEnumerable<AbstractImportMe> imports)
    {
        this.imports = imports;
    }
    */
}

然后我调用这段代码:

AggregateCatalog catalog = new AggregateCatalog(newAssemblyCatalog(Assembly.GetEntryAssembly().Location));
CompositionContainer container = new CompositionContainer(catalog);
Catalog catalog = container.GetExportedValue<Catalog>();

代码运行，但我没有得到任何 catalog.imports。当我查看目录时，会导出 1 个目录和一个 AbsractImportMe。

如前所述，当我从导入中排除元数据时，它工作正常。所以我认为我在元数据方面犯了一个错误。

Answer 1

我发现了问题，我需要向基类添加元数据标记以保持签名一致。由于导出是继承的，因此它保留了签名。

[InheritedExport(typeof(AbstractImportMe))] 
[SimpleMetadata("Abstract")]
public abstract class AbstractImportMe{

}