c# - 如何在 Autofac 注册中返回 NULL？

Question

有没有办法用 autofac 返回 null？如果我这样做，我会得到一个异常(exception)。

在某些情况下，我无法解析一个对象，应该返回 null。

m_builder.Register < IMyObject > ((c, p) => {
  //do something

  if (...) {
    //cant create/resolve object (error case)
    return null;
  } else {
    return new IMyObject();
  }

}).InstancePerHttpRequest();

是否有使用 autofac 执行此操作的内置方法？

编辑:我想返回空值。或者做点别的，通知用户创建不成功。如果我返回 null，将抛出此异常:

DependencyResolutionException:

A delegate registered to create instances of 'IMyObject' returned null.

堆栈跟踪:

at Autofac.Core.Activators.Delegate.DelegateActivator.ActivateInstance(IComponentContext context, IEnumerable1 parameters)<br/>
at Autofac.Core.Resolving.InstanceLookup.Activate(IEnumerable1 parameters)
at Autofac.Core.Resolving.InstanceLookup.b__0()
at Autofac.Core.Lifetime.LifetimeScope.GetOrCreateAndShare(Guid id, Func1 creator)<br/>
at Autofac.Core.Resolving.InstanceLookup.Execute()
at Autofac.Core.Resolving.ResolveOperation.GetOrCreateInstance(ISharingLifetimeScope
currentOperationScope, IComponentRegistration registration,
IEnumerable1 parameters)
at Autofac.Core.Resolving.ResolveOperation.Execute(IComponentRegistration registration, IEnumerable1 parameters)<br/>
at Autofac.Core.Lifetime.LifetimeScope.ResolveComponent(IComponentRegistration
registration, IEnumerable1 parameters)
at Autofac.ResolutionExtensions.TryResolveService(IComponentContext context, Service service, IEnumerable1 parameters, Object& instance)
at Autofac.ResolutionExtensions.ResolveService(IComponentContext
context, Service service, IEnumerable1 parameters)
at Autofac.ResolutionExtensions.Resolve[TService](IComponentContext context, IEnumerable`1 parameters)
at Autofac.ResolutionExtensions.Resolve[TService](IComponentContext context, Parameter[] parameters)
at RestApi.Controllers.MyApiController.CreateEntityContext() in C:...

Answer 1

据我所知，在注册中返回 NULL 总是会抛出异常。有关如何处理该问题的一些想法，请查看 this answer .