1、前言

前面的博客主要介绍了一些Autofac的使用方法，示例代码都是基于控制台程序。本文就来介绍一下如何在ASP.NET Core中使用Autofac代替内置的IoC容器。

2、创建接口和类

这里搭建了一个简易的项目，如下图所示：

Service层代码如下：

namespace App.Service.Contract
{public interface ICatService{string Get();}
}

namespace App.Service.Contract
{public interface IDogService{string Get();}
}

using App.Service.Contract;namespace App.Service
{public class CatService : ICatService{public string Get(){return "This is cat";}}
}

using App.Service.Contract;namespace App.Service
{public class DogService : IDogService{public string Get(){return "This is dog";}}
}

3、Autofac代替内置IoC容器

3.1、引入Autofac组件

新建一个Web API工程，使用NuGet引入如下组件：

Autofac
Autofac.Extensions.DependencyInjection

3.2、修改Program.cs

如果要使用Autofac代替内置的IoC容器，首先要对Program.cs进行修改，代码如下：

using Autofac.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;namespace App
{public class Program{public static void Main(string[] args){CreateHostBuilder(args).Build().Run();}public static IHostBuilder CreateHostBuilder(string[] args) =>Host.CreateDefaultBuilder(args).UseServiceProviderFactory(new AutofacServiceProviderFactory())  // Autofac代替内置IoC容器.ConfigureWebHostDefaults(webBuilder =>{webBuilder.UseStartup();});}
}

上面加了一句UseServiceProviderFactory(new AutofacServiceProviderFactory())，该方法可以重写用于创建服务提供程序的工厂，也就是说现在已经将其替换为Autofac对应的工厂了。

3.3、修改Startup.cs

在Startup.cs文件中，我们可以添加一个ConfigureContainer方法代替原有的ConfigureServices方法，代码如下：

using App.Service;
using App.Service.Contract;
using Autofac;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;namespace App
{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.AddControllers();}// Autofac注册接口和类public void ConfigureContainer(ContainerBuilder builder){builder.RegisterType().As().InstancePerLifetimeScope();builder.RegisterType().As().InstancePerLifetimeScope();}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseEndpoints(endpoints =>{endpoints.MapControllers();});}}
}

3.4、注入接口

创建一个控制器AnimalController，在构造函数中注入接口即可，代码如下：

using App.Service.Contract;
using Microsoft.AspNetCore.Mvc;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class AnimalController : ControllerBase{protected readonly ICatService _cat;protected readonly IDogService _dog;public AnimalController(ICatService cat, IDogService dog){_cat = cat;_dog = dog;}[HttpGet]public ActionResult Get(){return _cat.Get() + "\n" + _dog.Get();}}
}

运行结果如下所示：

This is cat
This is dog

3.5、单独配置Autofac模块

之前的博客介绍过，实际业务中一般会对Autofac进行单独配置。新建一个类AutofacModule，代码如下：

using App.Service;
using App.Service.Contract;
using Autofac;namespace App
{public class AutofacModule : Module{protected override void Load(ContainerBuilder builder){builder.RegisterType().As().InstancePerLifetimeScope();builder.RegisterType().As().InstancePerLifetimeScope();}}
}

修改一下Startup.cs文件，代码如下：

using Autofac;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;namespace App
{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.AddControllers();}// Autofac注册接口和类public void ConfigureContainer(ContainerBuilder builder){builder.RegisterModule(new AutofacModule());}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseEndpoints(endpoints =>{endpoints.MapControllers();});}}
}

运行程序，输出结果也是一样的：

This is cat
This is dog

4、结语

本文主要介绍了在ASP.NET Core中使用Autofac代替内置IoC容器的方法。相较于内置的IoC容器，Autofac功能更加丰富、使用更加灵活，在实际业务中合理使用Autofac可以极大提升开发效率，同时也更加便于项目后期的维护。