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Abp 源码分析（3）：DI 和 Autofac

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一、概述

Abp 的 DI 容器是基于 Microsoft 的依赖注入扩展库（Microsoft.Extensions.DependencyInjection nuget包）开发的。因此，它的文档在 Abp 中也是有效的。
Abp 中可以使用 Autofac 替换内置 DI 容器的，以支持属性注入和动态代理（拦截器）。

Abp 提供的服务自动注册功能用内置的 DI 容器也能实现。

二、使用 Autofac 替换内置 DI 容器

我们知道，.Net Core 中将服务的注册和服务的获取分别交给了 ServiceCollection 和 ServiceProvider。如果使用 Autofac，服务的注册继续使用 ServiceCollection。比如 Startup 的 ConfigureServices 方法等接收的是 IServiceCollection 型的参数。Abp 会将 ServiceColletion 中的服务重新注册入 Autofac，并且使用 AutofacServiceProvider 替换内置 ServiceProvider。

至少有三种方式可将内置的 DI 容器替换为 Autofac。

1、如何替换？

（1）、使用 Startup 的 ConfigureContainer 方法

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// File: Startup.cs
// ConfigureContainer is where you can register things directly
// with Autofac. This runs after ConfigureServices so the things
// here will override registrations made in ConfigureServices.
// Don't build the container; that gets done for you. If you
// need a reference to the container, you need to use the
// "Without ConfigureContainer" mechanism shown later.
public void ConfigureContainer(ContainerBuilder builder)
{
    builder.RegisterModule(new AutofacModule());
}

（2）、使用 Startup 的 ConfigureServices 方法

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// File: Startup.cs
// ConfigureServices is where you register dependencies. This gets
// called by the runtime before the Configure method, below.
public IServiceProvider ConfigureServices(IServiceCollection services)
{
    // Add services to the collection.
    services.AddMvc();

    // Create the container builder.
    var builder = new ContainerBuilder();

    // Register dependencies, populate the services from
    // the collection, and build the container.
    //
    // Note that Populate is basically a foreach to add things
    // into Autofac that are in the collection. If you register
    // things in Autofac BEFORE Populate then the stuff in the
    // ServiceCollection can override those things; if you register
    // AFTER Populate those registrations can override things
    // in the ServiceCollection. Mix and match as needed.
    builder.Populate(services);
    builder.RegisterType<MyType>().As<IMyType>();
    this.ApplicationContainer = builder.Build();

    // Create the IServiceProvider based on the container.
    return new AutofacServiceProvider(this.ApplicationContainer);
}

（3）、使用自定义 ServiceProviderFactory

Abp 自定义 ServiceProviderFactory，并且提供两种集成方案。

选择一：自行通过 ServiceProviderFactory 直接创建 ServiceProvider

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// File: abp\framework\src\Volo.Abp.Autofac\Volo\Abp\AbpAutofacAbpApplicationCreationOptionsExtensions.c
public static class AbpAutofacAbpApplicationCreationOptionsExtensions
{
    public static void UseAutofac(this AbpApplicationCreationOptions options)
    {
       ContainerBuilder builder = new ContainerBuilder();
       options.Services.AddObjectAccessor<ContainerBuilder>(builder);
       options.Services.AddSingleton<IServiceProviderFactory<ContainerBuilder>>((IServiceProviderFactory<ContainerBuilder>) new AbpAutofacServiceProviderFactory(builder));
    }
}

对应的 Startup.cs：

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// File: Startup.cs
// 返回 IServiceProvider 
public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.AddApplication<AppModule>(options =>{
        options.UseAutofac(); // 集成 Autofac
    });

    // 因为将 AbpAutofacServiceProviderFactory 注册为了 IServiceProviderFactory<ContainerBuilder> 的单例，所以 BuildServiceProviderFromFactory 可直接通过 ServceCollection 中获取实例。
    return services.BuildServiceProviderFromFactory(); 
}

ConfigureServices 需返回 IServiceProvider 参数以替换 DefaultServiceProvider。详见：StartupLoader 。

选择二：替换 ServiceProviderFactory

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// File: abp\framework\src\Volo.Abp.Autofac\Microsoft\Extensions\Hosting\AbpAutofacHostBuilderExtensions.cs
public static class AbpAutofacHostBuilderExtensions
{
    public static IHostBuilder UseAutofac(this IHostBuilder hostBuilder)
    {
        var containerBuilder = new ContainerBuilder();

        return hostBuilder.ConfigureServices((_, services) =>
            {
                services.AddObjectAccessor(containerBuilder);
            })
            .UseServiceProviderFactory(new AbpAutofacServiceProviderFactory(containerBuilder)); // 替换默认的 DefaultServiceProviderFactory ，详见 `HostBuilder` 。
    }
}

HostBuilder 默认包含一个 ServiceFactoryAdapter 对象，实际适配的是 DefaultServiceProviderFactory。HostBuilder.UseServiceProviderFactory 方法会构造一个新的ServiceFactoryAdapter 对象适配 AbpAutofacServiceProviderFactory。

对应的 Program.cs：

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// File: Program.cs
internal static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        })
        .UseAutofac() // 集成 Autofac
        .UseSerilog();

2、AbpAutofacServiceProviderFactory 类

AbpAutofacServiceProviderFactory 的作用是将注册入 ServiceCollection 中的服务转移入 Autofac 和生产出 AutofacServiceProvider 。
在ContainerBuilder CreateBuilder(IServiceCollection services) 方法中，将之前注册在 ServiceCollection 集合中的服务转移到 Autofac 中。并且启动了属性注入(Property injection)、拦截器(Interceptor)。
在IServiceProvider CreateServiceProvider(ContainerBuilder containerBuilder) 方法中，ContainerBuilder 构建一个 Autofac 容器，然后创建 AutofacServiceProvider 返回。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacServiceProviderFactory.cs
public class AutofacServiceProviderFactory : IServiceProviderFactory<ContainerBuilder> {

    private readonly Action<ContainerBuilder> _configurationAction;

    public AutofacServiceProviderFactory(Action<ContainerBuilder> 
configurationAction = null) {
        _configurationAction = configurationAction ?? (builder => { });
    }

    public ContainerBuilder CreateBuilder(IServiceCollection services) {
        var builder = new ContainerBuilder();
        // File: abp\framework\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacRegistration.cs
        // 将 ServiceCollection 填充入 ContainerBuilder
        builder.Populate(services);
        _configurationAction(builder);
        return builder;
    }

    public IServiceProvider CreateServiceProvider(ContainerBuilder 
containerBuilder) {
        if (containerBuilder == null) throw new ArgumentNullException(nameof(containerBuilder));
        var container = containerBuilder.Build();
        return new AutofacServiceProvider(container);
    }
}

将 ServiceProviderFactory、ContainerBuilder 和 ServiceProvider 三者的关系做个可能不太恰当的类比。ServiceProvider 是榨汁机，ContainerBuilder 是组装榨汁机的机器，ServiceProviderFactory 可以生产“组装榨汁机的机器”和通过该机器生产最终的“榨汁机”。榨汁机为我们提供榨汁服务。

扩展：AutofacServiceProviderFactory

对 AutofacRegistration 的深入分析请见下文。

3、AutofacServiceProvider 类

AbpServiceProvider 实际上是 Autofac 的适配器。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacServiceProvider.cs
public class AutofacServiceProvider : IServiceProvider, ISupportRequiredService {
    private readonly IComponentContext _componentContext;

    public AutofacServiceProvider(IComponentContext componentContext) {
        this._componentContext = componentContext;
    }

    public object GetRequiredService(Type serviceType) {
        return this._componentContext.Resolve(serviceType);
    }

    public object GetService(Type serviceType) {
        return this._componentContext.ResolveOptional(serviceType);
    }
}

4、AutofacServiceScope 类和 AutofacServiceScopeFactory 类

除了AbpServiceProvider , Abp 也用 AutofacServiceScope 和 AutofacServiceScopeFactory 对 Autofac 中相应的对象进行了适配。

三、深入 AutofacRegistration

AutofacRegistration 非常重要，它将 ServiceCollection 中注册的服务”填充”到 Autofac 中。

1、Populate 方法

Populate 首先将 AutofacServiceProvider 和 AutofacServiceScopeFactory 注册到 Autofac 中，然后调用 Regisster 私有方法。AutofacServiceScope 总是在 AutofacServiceScopeFactory 的 CreateScope 方法中直接 new 出来，所以不用注册。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacRegistration.cs
public static void Populate(this ContainerBuilder builder, IServiceCollection services) {
    builder.RegisterType<AutofacServiceProvider>().As<IServiceProvider>();
    builder.RegisterType<AutofacServiceScopeFactory>().As<IServiceScopeFactory>();
    Register(builder, services);
}

2、Register 方法

Register 是 AutofacRegistration 的核心方法。它将 ServiceCollection 中注册的服务重新注册入 Autofac 之外。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacRegistration.cs
private static void Register(ContainerBuilder builder, IServiceCollection services) {
    var moduleContainer = services.GetSingletonInstance<IModuleContainer>();
    var registrationActionList = services.GetRegistrationActionList();

    foreach (var service in services) {
        if (service.ImplementationType != null) {
            // Test if the an open generic type is being registered
            var serviceTypeInfo = service.ServiceType.GetTypeInfo();
            if (serviceTypeInfo.IsGenericTypeDefinition) {
                builder
                    .RegisterGeneric(service.ImplementationType)
                    .As(service.ServiceType)
                    .ConfigureLifecycle(service.Lifetime)
                    .ConfigureAbpConventions(moduleContainer, registrationActionList);
            } else {
                builder
                    .RegisterType(service.ImplementationType)
                    .As(service.ServiceType)
                    .ConfigureLifecycle(service.Lifetime)
                    .ConfigureAbpConventions(moduleContainer, registrationActionList);
            }
        } else if (service.ImplementationFactory != null) {
            var registration = RegistrationBuilder.ForDelegate(service.ServiceType, (context, parameters) => {
                var serviceProvider = context.Resolve<IServiceProvider>();
                return service.ImplementationFactory(serviceProvider);
            })
            .ConfigureLifecycle(service.Lifetime)
            .CreateRegistration();
            //TODO: ConfigureAbpConventions ?

            builder.RegisterComponent(registration);
        } else {
            builder
                .RegisterInstance(service.ImplementationInstance)
                .As(service.ServiceType)
                .ConfigureLifecycle(service.Lifetime);
        }
    }
}

AbpRegistrationBuilderExtensions.ConfigureAbpConventions 方法启用属性注入、收集拦截器(Interceptor) 并将之注册入 Autofac 中。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Builder\AbpRegistrationBuilderExtensions.cs
public static class AbpRegistrationBuilderExtensions
{
    public static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> ConfigureAbpConventions<TLimit, TActivatorData, TRegistrationStyle>(
            this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, 
            IModuleContainer moduleContainer, 
            ServiceRegistrationActionList registrationActionList)
        where TActivatorData : ReflectionActivatorData
    {
        var serviceType = registrationBuilder.RegistrationData.Services.OfType<IServiceWithType>().FirstOrDefault()?.ServiceType;
        if (serviceType == null)
        {
            return registrationBuilder;
        }

        var implementationType = registrationBuilder.ActivatorData.ImplementationType;
        if (implementationType == null)
        {
            return registrationBuilder;
        }

        // 启用属性注入
        registrationBuilder = registrationBuilder.EnablePropertyInjection(moduleContainer, implementationType);
        // 注册后续操作
        registrationBuilder = registrationBuilder.InvokeRegistrationActions(registrationActionList, serviceType, implementationType);

        return registrationBuilder;
    }
    // ...
 }

属性注入是 Autofac 的可选功能但 Apb 将之开启。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Builder\AbpRegistrationBuilderExtensions.cs
private static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> EnablePropertyInjection<TLimit, TActivatorData, TRegistrationStyle>(
        this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, 
        IModuleContainer moduleContainer,
        Type implementationType) 
    where TActivatorData : ReflectionActivatorData
{
    //Enable Property Injection only for types in an assembly containing an AbpModule
    if (moduleContainer.Modules.Any(m => m.Assembly == implementationType.Assembly))
    {
        registrationBuilder = registrationBuilder.PropertiesAutowired();
    }

    return registrationBuilder;
}

在 Abp 模块的 PreConfigureServices 方法中调用 ServiceCollectionRegistrationActionExtensions.OnRegister 扩展方法可以将某些“注册操作(Registration action)”放入全局的 ServiceRegistrationActionList : List<Action<IOnServiceRegistredContext>> 对象中。执行这些“注册操作”将可能导致拦截器添加到 OnServiceRegistredContext 中（如果“注册操作”的确是添加拦截器的话）。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Builder\AbpRegistrationBuilderExtensions.cs
private static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> InvokeRegistrationActions<TLimit, TActivatorData, TRegistrationStyle>(this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, ServiceRegistrationActionList registrationActionList, Type serviceType, Type implementationType) 
    where TActivatorData : ReflectionActivatorData
{
    var serviceRegistredArgs = new OnServiceRegistredContext(serviceType, implementationType);

    foreach (var registrationAction in registrationActionList)
    {
        // 执行注册操作
        registrationAction.Invoke(serviceRegistredArgs);
    }

    // 如果服务包含任意拦截器
    if (serviceRegistredArgs.Interceptors.Any())
    {
        registrationBuilder = registrationBuilder.AddInterceptors(
            serviceType,
            serviceRegistredArgs.Interceptors
        );
    }

    return registrationBuilder;
}

如果服务包含任意拦截器，则会创建代理类来拦截。

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// File: abp\framework\src\Volo.Abp.Autofac\Autofac\Builder\AbpRegistrationBuilderExtensions.cs
private static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> AddInterceptors<TLimit, TActivatorData, TRegistrationStyle>(
    this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, 
    Type serviceType,
    IEnumerable<Type> interceptors)
    where TActivatorData : ReflectionActivatorData
{
    if (serviceType.IsInterface)
    {
        registrationBuilder = registrationBuilder.EnableInterfaceInterceptors();
    }
    else
    {
        (registrationBuilder as IRegistrationBuilder<TLimit, ConcreteReflectionActivatorData, TRegistrationStyle>)?.EnableClassInterceptors();
    }

    foreach (var interceptor in interceptors)
    {
        // 创建代理类来拦截
        registrationBuilder.InterceptedBy(
            typeof(CastleAbpInterceptorAdapter<>).MakeGenericType(interceptor)
        );
    }

    return registrationBuilder;
}

只有 Abp 模块程序集中的类型才会开启属性注入，这就是 AbpRegistrationBuilderExtensions.ConfigureAbpConventions 方法接收一个 IModuleContainer 型参数的原因。通常 AbpApplication 是一个 Module container 。详见 AbpRegistrationBuilderExtensions.EnablePropertyInjection 方法。

 扩展：

 1、动态代理，见 CastleAbpInterceptorAdapter 。
 2、服务注册前后注册后进行某些操作，见 ServiceRegistrationActionList(ServiceCollectionRegistrationActionExtensions)、IExposedServiceTypesProvider、ExposedServiceExplorer 。

3、ConfigureLifecycle 方法

ConfigureLifecycle 方法比较简单，就是将 ServiceCollection 中注册的服务的生命周期，相应地配置到 Autofac 中。

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// File: abp\framewrok\src\Volo.Abp.Autofac\Autofac\Extensions\DependencyInjection\AutofacRegistration.cs
private static IRegistrationBuilder<object, TActivatorData, TRegistrationStyle> ConfigureLifecycle<TActivatorData, TRegistrationStyle>(
    this IRegistrationBuilder<object, TActivatorData, TRegistrationStyle> registrationBuilder,
    ServiceLifetime lifecycleKind) {
    switch (lifecycleKind) {
        case ServiceLifetime.Singleton:
            registrationBuilder.SingleInstance();
            break;
        case ServiceLifetime.Scoped:
            registrationBuilder.InstancePerLifetimeScope();
            break;
        case ServiceLifetime.Transient:
            registrationBuilder.InstancePerDependency();
            break;
    }

    return registrationBuilder;
}

参考资料