Autofac 如何根据上下文同时使用默认和非默认构造函数

Question

我有两个类喜欢：

public class P 
{
    public P( Guid g )  {}
}
public class Lp
{
    public Lp() {}
    public Lp( P p ) {}
}

我用 Autofac 6.2.0 注册了它们，例如：

builder.RegisterType< P >();
builder.RegisterType< Lp >();

现在我想使用默认构造函数解析 Lp。当我尝试像这样解决 Lp 时：

var c = builder.Build();
using( var scope = c.BeginLifetimeScope() )
{
   scope.Resolve<Lp>();
}

我收到一条错误消息，指出 none 类型 P 的构造函数可以使用可用的服务和参数调用。嗯，是的，这是真的。

显然，由于类型 P 已经被注册，Autofac 认为它应该能够创建一个 P 并使用它来创建 Lp 而不是认识到它没有创建没有 Guid 的 P 的方法，因此使用默认的 Lp ctor。如果我不注册P，解析成功。如果我将默认构造函数添加到 P，解析成功（除了它使用非默认 Lp 构造函数）。

诊断不是很有趣，但看起来像：

{   Resolve Request Starting   {
    Service: CtsMasterTs.Positions.Lp
    Component: CtsMasterTs.Positions.Lp

    Pipeline:
    -> CircularDependencyDetectorMiddleware
      -> ScopeSelectionMiddleware
        -> SharingMiddleware
          -> RegistrationPipelineInvokeMiddleware
            -> ActivatorErrorHandlingMiddleware
              -> DisposalTrackingMiddleware
                -> Lp (ReflectionActivator)
                  Resolve Request Starting
                  {
                    Service: CtsMasterTs.Positions.P
                    Component: CtsMasterTs.Positions.P

                    Pipeline:
                    -> CircularDependencyDetectorMiddleware
                      -> ScopeSelectionMiddleware
                        -> SharingMiddleware
                          -> RegistrationPipelineInvokeMiddleware
                            -> ActivatorErrorHandlingMiddleware
                              -> DisposalTrackingMiddleware
                                -> P (ReflectionActivator)
                                X- P (ReflectionActivator)
                              X- DisposalTrackingMiddleware
                            X- ActivatorErrorHandlingMiddleware
                          X- RegistrationPipelineInvokeMiddleware
                        X- SharingMiddleware
                      X- ScopeSelectionMiddleware
                    X- CircularDependencyDetectorMiddleware
                  }
                  Resolve Request FAILED
                    Autofac.Core.DependencyResolutionException: None of the constructors found with
'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type
'CtsMasterTs.Positions.P' can be invoked with the available services
and parameters:
                    Cannot resolve parameter 'System.Guid g' of constructor 'Void .ctor(System.Guid)'.
                       at Autofac.Core.Activators.Reflection.ReflectionActivator.GetAllBindings(ConstructorBinder[]
availableConstructors, IComponentContext context, IEnumerable`1
parameters) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
175
                       at Autofac.Core.Activators.Reflection.ReflectionActivator.ActivateInstance(IComponentContext
context, IEnumerable`1 parameters) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
134
                       at Autofac.Core.Activators.Reflection.ReflectionActivator.<ConfigurePipeline>b__11_0(ResolveRequestContext
ctxt, Action`1 next) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
104
                       at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
                       at Autofac.Core.Resolving.Middleware.DisposalTrackingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/DisposalTrackingMiddleware.cs:line
32
                       at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
                       at Autofac.Core.Resolving.Middleware.ActivatorErrorHandlingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/ActivatorErrorHandlingMiddleware.cs:line
36
                X- Lp (ReflectionActivator)
              X- DisposalTrackingMiddleware
            X- ActivatorErrorHandlingMiddleware
          X- RegistrationPipelineInvokeMiddleware
        X- SharingMiddleware
      X- ScopeSelectionMiddleware
    X- CircularDependencyDetectorMiddleware   }   Resolve Request FAILED: Nested Resolve Failed } Operation FAILED  
Autofac.Core.DependencyResolutionException: An exception was thrown
while activating CtsMasterTs.Positions.Lp -> CtsMasterTs.Positions.P.
---> Autofac.Core.DependencyResolutionException: None of the constructors found with
'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type
'CtsMasterTs.Positions.P' can be invoked with the available services
and parameters:   Cannot resolve parameter 'System.Guid g' of
constructor 'Void .ctor(System.Guid)'.
     at Autofac.Core.Activators.Reflection.ReflectionActivator.GetAllBindings(ConstructorBinder[]
availableConstructors, IComponentContext context, IEnumerable`1
parameters) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
175
     at Autofac.Core.Activators.Reflection.ReflectionActivator.ActivateInstance(IComponentContext
context, IEnumerable`1 parameters) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
134
     at Autofac.Core.Activators.Reflection.ReflectionActivator.<ConfigurePipeline>b__11_0(ResolveRequestContext
ctxt, Action`1 next) in
/_/src/Autofac/Core/Activators/Reflection/ReflectionActivator.cs:line
104
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Middleware.DisposalTrackingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/DisposalTrackingMiddleware.cs:line
32
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Middleware.ActivatorErrorHandlingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/ActivatorErrorHandlingMiddleware.cs:line
36
     --- End of inner exception stack trace ---
     at Autofac.Core.Resolving.Middleware.ActivatorErrorHandlingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/ActivatorErrorHandlingMiddleware.cs:line
48
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Middleware.SharingMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/SharingMiddleware.cs:line 58
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.Middleware.CircularDependencyDetectorMiddleware.Execute(ResolveRequestContext
context, Action`1 next) in
/_/src/Autofac/Core/Resolving/Middleware/CircularDependencyDetectorMiddleware.cs:line
94
     at Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__DisplayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
ctxt) in
/_/src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs:line
262
     at Autofac.Core.Resolving.ResolveOperation.GetOrCreateInstance(ISharingLifetimeScope
currentOperationScope, ResolveRequest request) in
/_/src/Autofac/Core/Resolving/ResolveOperation.cs:line 150
     at Autofac.Core.Resolving.ResolveOperation.ExecuteOperation(ResolveRequest
request) in /_/src/Autofac/Core/Resolving/ResolveOperation.cs:line 182

这对我来说是个问题，因为我需要能够在有或没有 P 的情况下创建 Lp。在代码的其他地方，我使用注入的 Func<Lp> 和 Func<P, Lp> 作为工厂。我还使用注入 Func<Guid, P> 来创建 P 个对象。

所以我的问题是 - 我该怎么做：

A) 让 Autofac 查看 P 构造函数并了解它不能使用没有 P 参数的非默认 Lp 构造函数，或者

B) 以其他方式（例如 lambda 注册？）发挥 Autofac 的魔力，让 Func<Lp> 和 Func<P, Lp> 都起作用？我已经简要地查看了使用 ctor 选择，但似乎每次解析类型时都会强制使用相同的 ctor。

其他信息 - .Net Framework 4.8、VS2019、Windows10、WPF。这是一个简化的示例，演示了我的（更复杂的）应用程序代码中发生的事情。

更新 - 这是代码味道吗？我仍在努力解决这个问题。

用例是 P 是不可变的。 Lp 是 P 的“可编辑”版本。当需要新 P 时，我使用默认构造函数创建一个新 Lp，编辑属性值，然后使用 Lp.CreateP( ).如果 P 已经存在并且需要编辑，我使用 Lp( P i_p ) 创建一个新的 Lp，编辑属性值，然后使用 [=61= 将原来的 P 替换为新的 P ]()。这对我来说似乎很合理，但也许我遗漏了什么。

Answer 1

这并不是一个常见的用例。绝大多数用法是：

Select the constructor that should always be used（要么使用带有 P 的构造函数，要么不使用，但不是“因上下文而异”）；或者
使用DI中最可用的东西可以填充的构造函数（这是Autofac的默认行为）

这个用例更像是...“我想使用默认的 Autofac 行为 _except 在这个嵌套范围内，我需要覆盖使用哪个构造函数。”我建议分析需要这样做的设计，因为它看起来像代码味道。

但是，您最好的办法是在子生命周期范围内重新注册 Lp 并强制使用您想要的构造函数。解决方案将根据覆盖发生，并且应该按照您的意愿进行。

var builder = new ContainerBuilder();
builder.RegisterType<P>();
builder.RegisterType<Lp>();
var container = builder.Build();

// This will use the `Lp(P)` constructor - most matched
var first = container.Resolve<Lp>();

using(var scope = container.BeginLifetimeScope(b =>
  {
    b.RegisterType<Lp>().UsingConstructor(Array.Empty<Type>());
  })
{
  // This should use the default no-parameter constructor.
  var second = scope.Resolve<Lp>();
}

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