无法从外部 DLL 加载接口的实现

Question

这是我的 Compose 部分，我在 dir Catalog THE RIGHT NUMBER that should be loaded 以及 asmCatalog 中看到。

public void Compose()
{
    var aggrCatalog = new AggregateCatalog();
    //A directory catalog
    var dirCatalog = new DirectoryCatalog(Path.GetDirectoryName(
        Assembly.GetExecutingAssembly().Location) + "\\Extensions", "*.dll");
    //An assembly catalog
    var asmCatalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());

    aggrCatalog.Catalogs.Add(dirCatalog);
    aggrCatalog.Catalogs.Add(asmCatalog);

    //Create a container THE CONTAINER DOES CONTAIN 5 PARTS AND
    // LOOK PERFECTLY OK. The 5 parts consist of 3 from this assembly 
    // and two from the external assembly
    var container = new CompositionContainer(aggrCatalog);

    // IT DOES NOT COMPOISE THE 2 PARTS THAT WERE LOADED FROM THE EXTERNAM ASSY
    container.ComposeParts(this);
}

我正在使用这个接口和属性：

namespace Q95Interface
{
    public interface IQ95_EventHandler
    {
        void HandleQ95Event();
        void HandleQ95Event(string s);
    }

    public interface IUIExtensionDetails
    {
        string Event_Group_Name { get; }
        string Event_Name { get; }
    }

    [MetadataAttribute]
    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
    public class Q95_EventHandlerAttribute : ExportAttribute
    {
        public Q95_EventHandlerAttribute() : base(typeof(IQ95_EventHandler)) { }

        public string Event_Group_Name { get; set; }
        public string Event_Name { get; set; }
    }
}

我要导入的实现是（本地程序集中的实现看起来相同并且加载和工作完美）

namespace MefTest
{
    [Export(typeof(IQ95_EventHandler))]
    [ExportMetadata("EventType", "START_ORDER_EXTERNAL")]
    public class Q95_Event_Handler4 : IQ95_EventHandler
    {
        public void HandleQ95Event() 
        { 
            Console.WriteLine("HANDLE EVENT START_ORDER"); 
        }
        public void HandleQ95Event(string s) { Console.WriteLine(s); }
    }

    [Export(typeof(IQ95_EventHandler))]
    [ExportMetadata("EventType", "STOP_ORDER_EXTERNAL")]
    public class Q95_Event_Handler5 : IQ95_EventHandler
    {
        public void HandleQ95Event() 
        { 
            Console.WriteLine("\nHANDLE EVENT STOP_ORDER\n"); 
        }
        public void HandleQ95Event(string s) { Console.WriteLine(s); }
    }
}

我已经分别编译成dll的接口和属性定义

Answer 1

您的[Import] 定义为什么？我怀疑这可能是因为您的导出不导出元数据。事实上，您已经创建了一个自定义的导出属性，但您并没有使用它。

尝试更改您的导出：

[Q95_EventHandler(Event_Group_Name = "Something", Event_Name = "Something Else")]
public class Q95_Event_Handler5 : IQ95_EventHandler
{

}

并确保您相应地导入：

[ImportMany]
public IEnumerable<Lazy<IQ95_EventHandler, IUIExtensionDetails>> Handlers { get; set; }

值得一看 Daniel Plaisted 的博客文章 How to Debug and Diagnose MEF Failures 以了解您可能遇到问题的地方。