"Autofac 逆变和解析开放的泛型类型"

Question

从 autofac 解析泛型类型（具有逆变 T）的所有实现时，我想获得所有可能的逆变匹配。 这仅在注册ContravariantRegistrationSource<\/em>时有效。 但是后来我得到了太多用于开放通用实现的实例，因为它遍历继承树为每个子类提供了一个实例。

这听起来可能有点抽象，所以这里有 2 个单元测试来演示这个问题。 他们都失败了，但我想让他们中的至少一个工作：

using Autofac;
using FluentAssertions;
using System.Collections.Generic;
using Xunit;
using Autofac.Features.Variance;

namespace Aiv.Vbr.QueryService.WebApi.Test.AdresMatchTests
{
    public class TestAutofacGenerics
    {
        public interface IGenericInterface<in T> { }
        public class GenericImplementation<T> : IGenericInterface<T> { }
        public class SpecificImplementation : IGenericInterface<TClass> { }
        public class TInterfaceImplementation : IGenericInterface<TInterface> { }
        public interface TInterface { }
        public class TClass : TInterface { }

        [Fact]
        public void AutofacShouldAlsoResolveContravariantImplementations()
        {
            var builder = new ContainerBuilder();
            builder.RegisterType<SpecificImplementation>().As<IGenericInterface<TClass>>();
            builder.RegisterType<TInterfaceImplementation>().As<IGenericInterface<TInterface>>();
            builder.RegisterGeneric(typeof(GenericImplementation<>)).As(typeof(IGenericInterface<>));

            var instances = builder.Build().Resolve<IEnumerable<IGenericInterface<TClass>>>();

            //This fails: only 2 types get resolved: GenericImplementation<TClass> and SpecificImplementation
            //but also expected TInterfaceImplementation
            instances.Should().HaveCount(3);
        }

        [Fact]
        public void AutofacShouldOnlyResolveOpenGenericsForSpecifiedClass()
        {
            var builder = new ContainerBuilder();
            builder.RegisterSource(new ContravariantRegistrationSource());
            builder.RegisterType<SpecificImplementation>().As<IGenericInterface<TClass>>();
            builder.RegisterType<TInterfaceImplementation>().As<IGenericInterface<TInterface>>();
            builder.RegisterGeneric(typeof(GenericImplementation<>)).As(typeof(IGenericInterface<>));

            var instances = builder.Build().Resolve<IEnumerable<IGenericInterface<TClass>>>();

            //This fails: 5 types get resolved: GenericImplementation<TClass>, GenericImplementation<Object>, 
            // GenericImplementation<TInterface>, SpecificImplementation and TInteraceImplementation
            //but did not want GenericImplementation<Object> and GenericImplementation<TInterface>
            instances.Should().HaveCount(3);
        }
    }    
}

Answer 1

该问题与ContravariantRegistrationSource<\/code>和RegisterGeneric<\/code>的工作方式有关

当您解决GenericImplementation<TClass><\/code>时， ContravariantRegistrationSource<\/code>将尝试解决

GenericImplementation<TClass>
GenericImplementation<Object>
GenericImplementation<TInterface>