IServiceCollection.AddHostedService <>(); 不解决

Question

我在一个全新的.net core 2 web应用程序中发生了一件奇怪的事情.这是Visual Studio中内置模板的标准Web api.VS 2017,所有的爵士乐.这是整个startup.cs:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using VerySimpleAPI.Helpers;

namespace VerySimpleAPI
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddHostedService<MainLoop>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseMvc(routes => {
                routes.MapRoute(
                    name: "Default",
                    template: "{controller}/{action}/{id?}",
                    defaults: new { controller = "Home", action = "Index"}
                    );
            });
        }
    }
}

MainLoop实施IHostedService和IDisposable.

该services.AddHostedService<MainLoop>();不能解决,产生错误"'IServiceCollection’不包含'AddHostedService’,没有扩展方法的定义......"所有的爵士乐.我检查了Microsoft.Extensions.DependencyInjection源代码,我清楚地看到了定义public static IServiceCollection AddHostedService<THostedService>(this IServiceCollection services)

没有托管服务引用,项目编译就好了.有什么我想念的吗？

Answer 1

AddHostedService是的一部分Microsoft.Extensions.Hosting.Abstractions.

虽然它是在定义的Microsoft.Extensions.DependencyInjection命名空间,它属于 Microsoft.Extensions.Hosting.Abstractions在ServiceCollectionHostedServiceExtensions类

using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.Extensions.Hosting;

namespace Microsoft.Extensions.DependencyInjection
{
    public static class ServiceCollectionHostedServiceExtensions
    {
        /// <summary>
        /// Add an <see cref="IHostedService"/> registration for the given type.
        /// </summary>
        /// <typeparam name="THostedService">An <see cref="IHostedService"/> to register.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to register with.</param>
        /// <returns>The original <see cref="IServiceCollection"/>.</returns>
        public static IServiceCollection AddHostedService<THostedService>(this IServiceCollection services)
            where THostedService : class, IHostedService
        {
            services.TryAddEnumerable(ServiceDescriptor.Singleton<IHostedService, THostedService>());

            return services;
        }
    }
}

并确保安装和引用相关软件包以访问扩展方法