c# - MEF2 和 .NET 核心

Question

我一直在阅读关于 MEF 还活着并且很好等等......
我也读到我只需要更换 void ConfigureServices(IServiceCollection services)为 IServiceCollection ConfigureServices(IServiceCollection services)提供我自己的容器(在我的情况下是 MEF 容器)...

我的问题是我无法找到正确的 return .你看，CompositionHost不实现 IServiceCollection ...

谁能教我如何在 .NET Core webapi 上使用 MEF2 作为我的容器？

Answer 1

这看起来很旧，我希望还为时不晚:D
您需要执行以下操作:
先决条件:Eml.MefBootstrapper

实现 IControllerActivator

//using System.Composition.Hosting;
//using Microsoft.AspNetCore.Mvc;
//using Microsoft.AspNetCore.Mvc.Controllers;
public class MefControllerActivator : IControllerActivator
{
       private readonly CompositionHost container;

       public MefControllerActivator(CompositionHost c) { container = c; }

       public object Create(ControllerContext c) => container.GetExport(c.ActionDescriptor.ControllerTypeInfo.AsType());

       public void Release(ControllerContext c, object controller) { }
}

创建您的扩展方法。 sample :

//using Eml.ClassFactory.Contracts;
//using Microsoft.AspNetCore.Hosting;
//using Microsoft.AspNetCore.Mvc.Controllers;
//using Microsoft.Extensions.DependencyInjection;
//using Microsoft.Extensions.Logging;
//using System;

    public static class MefService
    {
        /// <summary>
        /// Call this in Startup.ConfigureServices.
        /// Use Mef to resolve controllers. Hooks with ApplicationStopping for Mef disposal.
        /// Already have a reference to Eml.MefBootstrapper. Remove references to Eml.MefBootstrapper when using this to avoid version mismatch.
        /// </summary>
        /// <param name="serviceCollection"></param>
        /// <param name="bootstrapper"></param>
        public static IClassFactory AddMef(this IServiceCollection serviceCollection, Func<IClassFactory> bootstrapper)
        {
            var serviceProvider = serviceCollection.BuildServiceProvider();

            // Create Mef container
            var classFactory = bootstrapper();

            //Register MefControllerActivator
            serviceCollection.AddSingleton<IControllerActivator>(new MefControllerActivator(classFactory.Container));

            //Graceful exit
            var appLifetime = serviceProvider.GetService<IApplicationLifetime>();
            var loggerFactory = serviceProvider.GetService<ILoggerFactory>();

            appLifetime.ApplicationStopping.Register(() =>
            {
                var logger = loggerFactory.CreateLogger("Global logger");

                logger.LogDebug("Disposing Mef...");
                Eml.Mef.ClassFactory.Dispose(classFactory);
            });

            return classFactory;
        }
    }

创建要在 Startup.cs 中使用的 IServiceCollection 扩展

//using Eml.ClassFactory.Contracts;
//using Eml.Mef;
//using Microsoft.Extensions.DependencyInjection;
//using Microsoft.Extensions.Logging;
//using System;
//using System.Collections.Generic;
//using System.Composition.Hosting;
//using System.Composition.Hosting.Core;
//using Trackinator.Api.Helpers.Mef;
//using Trackinator.Infrastructure;

    public static class MefStartup
    {
        public static IClassFactory ConfigureMefService(this IServiceCollection services, ILoggerFactory loggerFactory)
        {
            return services.AddMef(() =>
            {
                // Register instances as shared.
                var instanceRegistrations = new List<Func<ContainerConfiguration, ExportDescriptorProvider>>
                {
                        r => r.WithInstance(loggerFactory)
                };

                // Create Mef container
                //return Bootstrapper.Init(Constants.ApplicationId, instanceRegistrations);
                var classFactory = Bootstrapper.Init(new List<string> { Constants.ApplicationId, "Microsoft.AspNetCore.SignalR." }, instanceRegistrations);
                
                return classFactory;
            });
        }
    }

将此行添加到 Startup.cs

public static IClassFactory ClassFactory { get; private set; }

public void ConfigureServices(IServiceCollection services)
{
    //..other codes
    ClassFactory = services.ConfigureMefService(LoggerFactory);

}

查看示例实现 here
祝你好运!