MEF2与.NET核心

Question

我一直在读到MEF还活着等等.

我还读到，我只需要替换void ConfigureServices(IServiceCollection services)，IServiceCollection ConfigureServices(IServiceCollection services)就可以提供我自己的容器(在我的例子中，MEF容器).

我的问题是我找不到正确的return。你看，CompositionHost没有实现IServiceCollection..。

有人能教我如何使用MEF2作为.NET核心webapi上的容器吗？

Answer 1

这似乎很旧，我希望不会太晚。

下面是你需要做的事情：

先决条件：Eml.MefBootstrapper

1. 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) { }
}

1. 创建扩展方法。示例：

//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;
        }
    }

1. 创建IServiceCollection扩展以在Startup.cs中使用

//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;
            });
        }
    }

1. 将这一行添加到Startup.cs中

public static IClassFactory ClassFactory { get; private set; }

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

}

参见示例实现这里

祝好运!