理解ASP.NETCore依赖注入(DependencyInjection)

public class FileLogger
{
    public void LogInfo(string message)
    {

    }
}

public class MyService
{
    private readonly FileLogger _logger = new FileLogger();

    public void Get()
    {
        _logger.LogInfo("MyService.Get");
    }
}

public class MyService
{
    private readonly ElkLogger _logger = new ElkLogger();

    public void Get()
    {
        _logger.LogInfo("MyService.Get");
    }
}

public class Service1 : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Service1.Dispose");
    }
}

public class Service2 : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Service2.Dispose");
    }
}

public class Service3 : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Service3.Dispose");
    }
}

public class Service4 : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Service4.Dispose");
    }
}

public void ConfigureServices(IServiceCollection services)
{
    // 每次使用完（请求结束时）即释放
    services.AddTransient();
    // 超出范围（请求结束时）则释放
    services.AddScoped();
    // 程序停止时释放
    services.AddSingleton();
    // 程序停止时释放
    services.AddSingleton(sp => new Service4());
}

public ValuesController(
    Service1 service1, 
    Service2 service2, 
    Service3 service3, 
    Service4 service4)
{ }

public void ConfigureServices(IServiceCollection services)
{
    // 注意与上面的区别，这个是直接 new 的，而上面是通过 sp => new 的
    services.AddSingleton(new Service1());
    services.AddSingleton(new Service2());
    services.AddSingleton(new Service3());
    services.AddSingleton(new Service4());
}

services.AddSingleton();
services.AddSingleton();

services.AddTransient();
// 由于上面已经注册了服务类型 IMyService，所以下面的代码不不会执行任何操作（与生命周期无关）
services.TryAddTransient();
services.TryAddTransient();

// 注册了 IMyService - MyService1
services.TryAddEnumerable(ServiceDescriptor.Singleton());
// 注册了 IMyService - MyService2
services.TryAddEnumerable(ServiceDescriptor.Singleton());
// 未进行任何操作，因为 IMyService - MyService1 在上面已经注册了
services.TryAddEnumerable(ServiceDescriptor.Singleton());

public interface IAnimalService { }
public class DogService : IAnimalService { }
public class PigService : IAnimalService { }
public class CatService : IAnimalService { }

public void ConfigureServices(IServiceCollection services)
{
    // 生命周期没有限制
    services.AddTransient();
    services.AddScoped();
    services.AddSingleton();
}

public ValuesController(
    // CatService
    IAnimalService animalService,   
    // DogService、PigService、CatService
    IEnumerable animalServices)
{
}

// 将 IMyService 的实现替换为 MyService1
services.Replace(ServiceDescriptor.Singleton());
// 移除 IMyService 注册的实现 MyService
services.Remove(ServiceDescriptor.Singleton());
// 移除 IMyService 的所有注册
services.RemoveAll();
// 清除所有服务注册
services.Clear();

Install-Package Autofac
Install-Package Autofac.Extensions.DependencyInjection

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup();
        })
        // 通过此处将默认服务提供器工厂替换为 autofac
        .UseServiceProviderFactory(new AutofacServiceProviderFactory());

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        COnfiguration= configuration;
    }

    public IConfiguration Configuration { get; }

    public ILifetimeScope AutofacContainer { get; private set; }

    public void ConfigureServices(IServiceCollection services)
    {
        // 1. 不要 build 或返回任何 IServiceProvider，否则会导致 ConfigureContainer 方法不被调用。
        // 2. 不要创建 ContainerBuilder，也不要调用 builder.Populate()，AutofacServiceProviderFactory 已经做了这些工作了
        // 3. 你仍然可以在此处通过微软默认的方式进行服务注册
        
        services.AddOptions();
        services.AddControllers();
        services.AddSwaggerGen(c =>
        {
            c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApplication.Ex", Version = "v1" });
        });
    }

    // 1. ConfigureContainer 用于使用 Autofac 进行服务注册
    // 2. 该方法在 ConfigureServices 之后运行，所以这里的注册会覆盖之前的注册
    // 3. 不要 build 容器，不要调用 builder.Populate()，AutofacServiceProviderFactory 已经做了这些工作了
    public void ConfigureContainer(ContainerBuilder builder)
    {
        // 将服务注册划分为模块，进行注册
        builder.RegisterModule(new AutofacModule());
    }
    
    public class AutofacModule : Autofac.Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            // 在此处进行服务注册
            builder.RegisterType().As();
        }
    }

    public void Configure(IApplicationBuilder app, ILoggerFactory loggerFactory)
    {
        // 通过此方法获取 autofac 的 DI容器
        AutofacCOntainer= app.ApplicationServices.GetAutofacRoot();
    }
}

[HttpGet]
public string Get([FromServices]IMyService myService)
{
    return "Ok";
}

public interface IUserService 
{
    string Get();
}

public class UserService : IUserService
{
    public string Get()
    {
        return "User";
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers().AddControllersAsServices();
}

public void ConfigureContainer(ContainerBuilder builder)
{
    builder.RegisterModule();
}

public class AutofacModule : Autofac.Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterType().As();

        var cOntrollerTypes= Assembly.GetExecutingAssembly().GetExportedTypes()
            .Where(type => typeof(ControllerBase).IsAssignableFrom(type))
            .ToArray();

        // 配置所有控制器均支持属性注入
        builder.RegisterTypes(controllerTypes).PropertiesAutowired();
    }
}

public class ValuesController : ControllerBase
{
    public IUserService UserService { get; set; }

    [HttpGet]
    public string Get()
    {
        return UserService.Get();
    }
}

using Microsoft.Extensions.DependencyInjection;

public class ValuesController : ControllerBase
{
    private readonly IServiceProvider _serviceProvider;

    // 应通过依赖注入的方式获取服务实例
    public ValuesController(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    [HttpGet]
    public string Get()
    {
        // 尽量避免通过 GetService 方法获取服务实例
        var myService = _serviceProvider.GetService();

        return "Ok";
    }
}

public void ConfigureServices(IServiceCollection services)
{
    // 不要在该方法中调用该方法
    var serviceProvider = services.BuildServiceProvider();
}

namespace Microsoft.Extensions.DependencyInjection
{
    public static class ApplicationServiceCollectionExtensions
    {
        public static IServiceCollection AddApplicationService(this IServiceCollection services)
        {
            services.AddTransient();
            services.AddScoped();
            services.AddSingleton();
            services.AddSingleton(sp => new Service4());

            return services;
        }
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddApplicationService();
}