[Asp.net 5] DependencyInjection项目代码分析2-Autofac

Microsoft.Framework.DependencyInjection.Autofac源码分析

该工程只有一个代码静态类AutofacRegistration，但是该类有3个扩展方法，以及3个内部类。扩展方法如下：

public static class AutofacRegistration
    {
          public static void Populate(this ContainerBuilder builder,IEnumerable<ServiceDescriptor> descriptors);

           private static void Register(ContainerBuilder builder,IEnumerable<ServiceDescriptor> descriptors);

           private static IRegistrationBuilder<object, T, U> ConfigureLifecycle<T, U>(this IRegistrationBuilder<object, T, U> registrationBuilder,ServiceLifetime lifecycleKind)
    }

在Autofac中，ContainerBuilder是用于类型注册的，3个扩展方法都是基于此展开的。

Populate方法如下：先对IServiceProvider、IServiceScopeFactory接口进行注册，之后调用Register方法，对于外部的具体类型进行注册。该方法的入参是IEnumerable<ServiceDescriptor> descriptors类型，所以参数可以直接使用IServiceCollection（也就是List<ServiceDescriptor>）。

public static void Populate(this ContainerBuilder builder,
                            IEnumerable<ServiceDescriptor> descriptors)
        {
            builder.RegisterType<AutofacServiceProvider>().As<IServiceProvider>();
            builder.RegisterType<AutofacServiceScopeFactory>().As<IServiceScopeFactory>();

            Register(builder, descriptors);
        }

对于Register方法相对复杂些，需要将ServiceDescriptor对象转化为实际的注册类型，代码如下所示：

private static void Register(
                ContainerBuilder builder,
                IEnumerable<ServiceDescriptor> descriptors)
        {
            foreach (var descriptor in descriptors)
            {
                if (descriptor.ImplementationType != null)
                {
                    // Test if the an open generic type is being registered
                    var serviceTypeInfo = descriptor.ServiceType.GetTypeInfo();
                    if (serviceTypeInfo.IsGenericTypeDefinition)
                    {
                        builder
                            .RegisterGeneric(descriptor.ImplementationType)
                            .As(descriptor.ServiceType)
                            .ConfigureLifecycle(descriptor.Lifetime);
                    }
                    else
                    {
                        builder
                            .RegisterType(descriptor.ImplementationType)
                            .As(descriptor.ServiceType)
                            .ConfigureLifecycle(descriptor.Lifetime);
                    }
                }
                else if (descriptor.ImplementationFactory != null)
                {
                    var registration = RegistrationBuilder.ForDelegate(descriptor.ServiceType, (context, parameters) =>
                    {
                        var serviceProvider = context.Resolve<IServiceProvider>();
                        return descriptor.ImplementationFactory(serviceProvider);
                    })
                    .ConfigureLifecycle(descriptor.Lifetime)
                    .CreateRegistration();

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

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