将MEF与抽象基类一起使用 [英] Using MEF with abstract base class

问题描述

我正在构建数据库导入应用程序，而不是我希望它具有可扩展性(可以根据需要添加自定义数据库模型).我的基本组件具有扩展类型必须实现的方法:MapData&保存数据.

I'm building a database import app than I want to be extensible (custom db models can be added as needed). My base component has methods that extended types have to implement: MapData & SaveData.

我将基类定义为抽象类，并且当扩展类型位于相同的名称空间中时，所有方法都可以正常工作.但是，我想在运行时使用MEF在其他名称空间中导入扩展类型，但是我不知道该怎么做.

I defined the base as an abstract class, and everything works when the extended types are in the same namespace. However, I want to use MEF to import extended types in a different namespace at runtime, but I can't figure out how to do that.

基类:

namespace Program
{
   public abstract class Component
   {
      public abstract string TypeName { get; }
      public abstract DataSet MapData( DataSet db );
      public abstract bool SaveData();
   }
}

扩展类(在单独的项目中):

Extended class (in a separate project):

using Program.Component;
namespace ExtendedType
{
   [Export( typeof( Component )]
   class Type1 : Component
   {
       public override string TypeName { get { return "Type1" } }
       public override DataSet MapData( DataSet db )
       {
          // create various object models from db here 
          return db;
       }
       public override bool SaveData()
       {
          // save object models 
          return true;
       }
   }
}

程序用于导入所有扩展类型:

Program to import all extended types:

namespace Program
{
   [ImportMany( typeof( Component ) )]
   public IEnumerable<Component> componentTypes;

   public Program()
   {
        var catalog = new AggregateCatalog();
        catalog.Catalogs.Add( new AssemblyCatalog( typeof( Component ).Assembly ) );
        container = new CompositionContainer( catalog );
        this.container.ComposeParts( this );
   }
}

根据我所读的内容，IEnumerable上的[ImportMany]属性应在运行时填充该属性，但它始终为空. CompositionContainer也始终为空.

According to what I've read, the [ImportMany] attribute on IEnumerable should fill that at runtime but it's always empty. The CompositionContainer is always empty as well.

我设置不正确是什么?如何获得扩展组件类型的列表?

What did I set up incorrectly? How can I get a list of the extended Component types?

推荐答案

我最终创建了一个供MEF组件使用的扩展目录，并在App.Config中设置了一个变量，并将其他项目的Build目录设置为指向那里.感谢@JaredPar的帮助.

I ended up creating an Extensions directory for the MEF components to live in and setting a variable in App.Config as well as the Build directory of the other projects to point there. Thanks to @JaredPar for the help.

 var extensionFolder = ConfigurationManager.AppSettings["ExtensionPath"];
 var solutionPath = Directory.GetParent( System.IO.Directory.GetCurrentDirectory() ).Parent.FullName;
 var catalog = new AggregateCatalog();
 catalog.Catalogs.Add( new DirectoryCatalog( solutionPath + extensionFolder ) );
 var container = new CompositionContainer( catalog );
 container.ComposeParts( this );

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