MEF:从类型获取GetExportedValue吗? [英] MEF: GetExportedValue from Type?

问题描述

使用MEF，我可以创建和加载这样的类型:

Using MEF I can create and load a type like this:

var view = Container.GetExportedValue<MyView>();

现在我要做的是:

Type t = typeof(MyView);
var view = Container.GetExportedValue<t>();

(当然，该类型可能包含与MyView不同的内容).

(of course the type might contain something different than MyView).

使用泛型GetExportedValue不可能做到这一点-还有其他方法可以实现这一点吗?

This is not possible using the generics GetExportedValue<> - is there some other way to achieve this?

推荐答案

您可以使用反射.
这是一个示例:

You can use reflection.
Here is an example:

using System;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.Linq;
using System.Reflection;

namespace WindowsFormsApplication1
{
    static class Program
    {
        [STAThread]
        static void Main()
        {
            AggregateCatalog catalog = new AggregateCatalog();
            catalog.Catalogs.Add(new AssemblyCatalog(typeof(IMessage).Assembly));
            CompositionContainer container = new CompositionContainer(catalog);

            Type t = typeof(IMessage);
            var m = container.GetExportedValue(t);
        }
    }

    public static class CompositionContainerExtension
    {
        public static object GetExportedValue(this ExportProvider container, Type type)
        {
            // get a reference to the GetExportedValue<T> method
            MethodInfo methodInfo = container.GetType().GetMethods()
                                      .Where(d => d.Name == "GetExportedValue"
                                                  && d.GetParameters().Length == 0).First();

            // create an array of the generic types that the GetExportedValue<T> method expects
            Type[] genericTypeArray = new Type[] { type };

            // add the generic types to the method
            methodInfo = methodInfo.MakeGenericMethod(genericTypeArray);

            // invoke GetExportedValue<type>()
            return methodInfo.Invoke(container, null);
        }
    }

    public interface IMessage
    {
        string Message { get; }
    }

    [Export(typeof(IMessage))]
    public class MyMessage : IMessage
    {
        public string Message
        {
            get { return "test"; }
        }
    }
}

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