【问题标题】：Dependency injection in ASP.NET Core 2 issueASP.NET Core 2 中的依赖注入问题
【发布时间】：2018-08-20 21:12:11
【问题描述】：

更新

我把启动改成：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Actio.Api.Handlers;
using Actio.Api.Repositories;
using Actio.Common.Auth;
using Actio.Common.Events;
using Actio.Common.Mongo;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Actio.Api
{
    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.AddJwt(Configuration);
            services.AddRabbitMq(Configuration);
            services.AddMongoDB(Configuration);
            services.AddScoped<IEventHandler<ActivityCreated>, ActivityCreatedHandler>();
            services.AddScoped<IActivityRepository, ActivityRepository>();

        }

        // 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.ApplicationServices.GetService<IDatabaseInitializer>().InitializeAsync();

            using (var serviceScope = app.ApplicationServices.CreateScope())
            {
                serviceScope.ServiceProvider.GetService<IDatabaseInitializer>().InitializeAsync();
            }
            app.UseAuthentication();
            app.UseMvc();
        }
    }
}

但现在我在 SubscribeToEvent 中遇到错误：无法解析范围服务

'Actio.Common.Events.IEventHandler`1[Actio.Common.Events.ActivityCreated]' from root provider.'

在我的 ServiceHost.cs 中。

ServiceHost.cs

using System;
using Actio.Common.Commands;
using Actio.Common.Events;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using RawRabbit;

namespace Actio.Common.Services
{
    public class ServiceHost : IServiceHost
    {
        private readonly IWebHost _webHost;

        public ServiceHost(IWebHost webHost)
        {
            _webHost = webHost;
        }

        public void Run() => _webHost.Run();

        public static HostBuilder Create<TStartup>(string[] args) where TStartup : class
        {
            Console.Title = typeof(TStartup).Namespace;
            var config = new ConfigurationBuilder()
                .AddEnvironmentVariables()
                .AddCommandLine(args)
                .Build();
            var webHostBuilder = WebHost.CreateDefaultBuilder(args)
                .UseConfiguration(config)
                .UseStartup<TStartup>();

            return new HostBuilder(webHostBuilder.Build());
        }

        public abstract class BuilderBase 
        {
            public abstract ServiceHost Build();
        }

        public class HostBuilder : BuilderBase
        {
            private readonly IWebHost _webHost;
            private IBusClient _bus;

            public HostBuilder(IWebHost webHost)
            {
                _webHost = webHost;
            }

            public BusBuilder UseRabbitMq()
            {
                _bus = (IBusClient)_webHost.Services.GetService(typeof(IBusClient));

                return new BusBuilder(_webHost, _bus);
            }

            public override ServiceHost Build()
            {
                return new ServiceHost(_webHost);
            }
        }

        public class BusBuilder : BuilderBase
        {
            private readonly IWebHost _webHost;
            private IBusClient _bus; 

            public BusBuilder(IWebHost webHost, IBusClient bus)
            {
                _webHost = webHost;
                _bus = bus;
            }

            public BusBuilder SubscribeToCommand<TCommand>() where TCommand : ICommand
            {
                var handler = (ICommandHandler<TCommand>)_webHost.Services
                    .GetService(typeof(ICommandHandler<TCommand>));
                _bus.WithCommandHandlerAsync(handler);

                return this;
            }

            public BusBuilder SubscribeToEvent<TEvent>() where TEvent : IEvent
            {
                var handler = (IEventHandler<TEvent>)_webHost.Services
                    .GetService(typeof(IEventHandler<TEvent>));
                _bus.WithEventHandlerAsync(handler);

                return this;
            }

            public override ServiceHost Build()
            {
                return new ServiceHost(_webHost);
            }
        }
    }
}

---------------------------------------------- -------------------------------------------

我最近开始使用 RabbitMQ 学习微服务。经过一番努力，我得到了一个代码示例，但我无法运行它，因为它给出了错误:"System.InvalidOperationException: 'Cannot resolve scoped service 'Actio.Common.Mongo.IDatabaseInitializer' from root provider.'"

我希望了解这段代码，以便更好地了解微服务。

代码启动.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Actio.Api.Handlers;
using Actio.Api.Repositories;
using Actio.Common.Auth;
using Actio.Common.Events;
using Actio.Common.Mongo;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Actio.Api
{
    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.AddJwt(Configuration);
            services.AddRabbitMq(Configuration);
            services.AddMongoDB(Configuration);
            services.AddScoped<IEventHandler<ActivityCreated>, ActivityCreatedHandler>();
            services.AddScoped<IActivityRepository, ActivityRepository>();
        }

        // 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();
            }
          //Giving Error in below line


app.ApplicationServices.GetService<IDatabaseInitializer>().InitializeAsync();
                app.UseAuthentication();
                app.UseMvc();
            }
        }
    }

谁能帮我调试一下，让我有更好的理解。

谢谢

【问题讨论】：

你是否在你的 DI 中设置了 IDatabaseInitializer？
是的。我有。 '使用 System.Threading.Tasks;命名空间 Actio.Common.Mongo { 公共接口 IDatabaseInitializer { 任务 InitializeAsync(); } }

标签： c# asp.net-core rabbitmq microservices

【解决方案1】：

以下错误试图告诉您您正在将IDatabaseInitializer 注册为范围服务，但尝试在范围之外访问它：

"System.InvalidOperationException: 'Cannot resolve scoped service 'Actio.Common.Mongo.IDatabaseInitializer' from root provider.'"

尝试创建一个范围，然后使用如下服务：

using (var serviceScope = app.ApplicationServices.CreateScope())
{
    serviceScope.ServiceProvider.GetService<IDatabaseInitializer>().InitializeAsync();
}

【讨论】：

谢谢。我改了，但 SubscribeToEvent 方法又出现了一些错误。任何帮助

【解决方案2】：

解决方案是禁用范围验证。

所以在文件 src\actio.common\services\servicehost.cs 的第 31-32 行之间添加以下内容：

.UseDefaultServiceProvider(options => options.ValidateScopes = false)

解决问题的另一种替代方法是在 program.cs 中将 services.AddScoped 更改为 services.AddSingleton，使用单例也可以避免所有范围验证。

【讨论】：