获取错误未找到与约束匹配的有效导出 [英] Getting Error in No valid exports were found that match the constraint

问题描述

运行以下程序时，我得到

While running the following Program i am getting the

组合不变。由于以下错误，更改被拒绝：组合生成单个组合错误。根本原因如下。查看CompositionException.Errors属性以获取更详细的信息。

The composition remains unchanged. The changes were rejected because of the following error(s): The composition produced a single composition error. The root cause is provided below. Review the CompositionException.Errors property for more detailed information.

1）没有找到与约束匹配的有效导出（（exportDefinition.ContractName ==System.Collections。 （ExportDefinition.Metadata.gettainItem（ExportTypeIdentity））和AndAlso（ExportDefinition.Metadata.ContainsKey（ExportTypeIdentity）AndAlsoSystem.Collections.Generic.IEnumerable（MEF.IToolWindow） ））），无效的导出可能已被拒绝。

1) No valid exports were found that match the constraint '((exportDefinition.ContractName == "System.Collections.Generic.IEnumerable(MEF.IToolWindow)") AndAlso (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") AndAlso "System.Collections.Generic.IEnumerable(MEF.IToolWindow)".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))', invalid exports may have been rejected.

导致：无法设置import'MEF.Program + Application.ToolWindows（ContractName =System.Collections.Generic 。部分'MEF.Program + Application'上的.IEnumerable（MEF.IToolWindow））'。
元素：MEF.Program + Application.ToolWindows（ContractName =System.Collections.Generic.IEnumerable（MEF.IToolWindow）） - > MEF.Program + Application

Resulting in: Cannot set import 'MEF.Program+Application.ToolWindows (ContractName="System.Collections.Generic.IEnumerable(MEF.IToolWindow)")' on part 'MEF.Program+Application'. Element: MEF.Program+Application.ToolWindows (ContractName="System.Collections.Generic.IEnumerable(MEF.IToolWindow)") --> MEF.Program+Application

代码在此处

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Primitives;
using System.ComponentModel.Composition.Hosting;
using System.Collections;

//Without MEF
namespace MEF
{
    public interface IToolWindow
    {
        string Name { get; set; }
    }
    public interface IMenuService
    {
        IMenu GetMenu(string menuName);
    }

    public interface IMenuItem
    {
        string Name { get; set; }
        string Title { get; set; }
        Action Handler { get; set; }
    }

    public interface IMenu
    {
        string Name { get; set; }
        string Title { get; set; }
        string ToolWindow { get; set; }
        IEnumerable<IMenuItem> Items { get; set; }
        IMenuItem GetItem(string itemName);
    }

    //public interface IMenuItem<> :IMenuItem{}
class Program
{
    static void Main(string[] args)
    {
        var container = new CompositionContainer();
        var compositionBatch = new CompositionBatch();

        var someToolWindow = new SomeToolWindow();
        var application = new Application();
        var menuService = new MenuService();

        compositionBatch.AddPart(application);
        compositionBatch.AddPart(someToolWindow);
        compositionBatch.AddPart(menuService);


        container.Compose(compositionBatch);

        //application.ToolWindows = new List<IToolWindow>{someToolWindow};
        //someToolWindow.MenuService = menuService;


        foreach(var window in application.ToolWindows)
            Console.WriteLine(window.Name);
        Console.WriteLine(someToolWindow.MenuService);
        Console.ReadLine();
    }



    public class Application
    {
        [Import]
        public IEnumerable<IToolWindow> ToolWindows{get;set;}

        public IToolWindow GetWindow(string windowName)
        {
            return ToolWindows.Where(w =>w.Name == windowName).FirstOrDefault();
        }
    }

    [Export(typeof(IToolWindow))]
    public class SomeToolWindow : IToolWindow
    {
        [Import]
        public IMenuService MenuService { get; set; }
        public string Name { get; set; }
        public string Title { get; set; }

    }

    [Export(typeof(IMenuService))]
    public class MenuService:IMenuService
    {
        public IEnumerable<IMenu> Menus {get;set;}
        public IMenu  GetMenu(string menuName)
        {
            return Menus.Where(m => m.Name == menuName).FirstOrDefault();
        }
    }
}

}

任何人都有想法？

推荐答案

[ImportMany]如果要填充列表。我测试了下面的代码并且工作。

You need to change the [Import] to [ImportMany] if you want to populate a list. I tested the code below and it works.

   public class Application
   {
       [ImportMany]
       public IEnumerable<IToolWindow> ToolWindows { get; set; }

       public IToolWindow GetWindow(string windowName)
       {
           return ToolWindows.Where(w => w.Name == windowName).FirstOrDefault();
       }
   }

此外，您还需要为SomeToolWindow添加一个名称if你想要它打印它。

Also you will need to add a name to SomeToolWindow if you want it to print it.

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