MEF在WebApi中应用

1.MEF在MVC中和在WebApi中的初始化，是用区别的，他们分别实现的接口如下：

//WebApi需要实现的接口
System.Web.Http.Dependencies.IDependencyResolver
//MVC需要实现的接口
System.Web.Mvc.IDependencyResolver

2.MEF的代码如下：

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.ComponentModel.Composition.Primitives;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using System.Web.Http.Dependencies;

namespace Test.Domain.Infrastructure.Ioc
{
    public class MefDependencySolver : System.Web.Http.Dependencies.IDependencyResolver, System.Web.Mvc.IDependencyResolver//: IDependencyResolver
    {
        private readonly ComposablePartCatalog _catalog;
        private const string MefContainerKey = "MefContainerKey";

        public MefDependencySolver(ComposablePartCatalog catalog)
        {
            _catalog = catalog;
        }

        public CompositionContainer Container
        {
            get
            {
                if (!HttpContext.Current.Items.Contains(MefContainerKey))
                {
                    HttpContext.Current.Items.Add(MefContainerKey, new CompositionContainer(_catalog));
                }
                CompositionContainer container = (CompositionContainer)HttpContext.Current.Items[MefContainerKey];
                HttpContext.Current.Application["Container"] = container;
                return container;
            }
        }

        #region IDependencyResolver Members

        public object GetService(Type serviceType)
        {
           string contractName = AttributedModelServices.GetContractName(serviceType);
            return Container.GetExportedValueOrDefault<object>(contractName);
        }

        public IEnumerable<object> GetServices(Type serviceType)
        {
            return Container.GetExportedValues<object>(serviceType.FullName);
        }

        #endregion

        /// <summary>
        /// BeginScope
        /// </summary>
        /// <returns></returns>
        public IDependencyScope BeginScope()
        {
            return new MefDependencySolver(_catalog);
        }

        public void Dispose()
        {
            //ToDo
        }

    }
}

3.在WebApiConfig.cs文件中，设置MEF的初始化，代码如下：

//初始化MEF配置
DirectoryCatalog catalog = new DirectoryCatalog(AppDomain.CurrentDomain.SetupInformation.PrivateBinPath);
MefDependencySolver solver = new MefDependencySolver(catalog);
config.DependencyResolver = solver;

转自：https://blog.csdn.net/allenwdj/article/details/50509340?t=1484492702237