使用 autofac 解析在运行时在构造函数中接受参数的类实例

Question

我正在按照下面的示例使用 autofac 在运行时创建一个类实例。 http://autofaccn.readthedocs.io/en/latest/advanced/delegate-factories.html

但是在本地运行时，我看到了一个异常。我是 autofac 的新手，如果我在这里做错了什么或者您需要更多信息，请告诉我。

代码结构：

public class ClassName
{
    public delegate ClassName Factory(Type1 obj1, string obj2);
    public ClassName(Type1 obj1, string obj2)
    {
        this.type1 = obj1;
        this.type2= obj2;
    }

    /*Some methods of this class that use type1 and type2*/
}

// Registration 
container.RegisterType<Type1>();
container.RegisterType<ClassName.Factory>();
container.RegisterType<ClassName>().AsSelf().InstancePerDependency();

// In some method to create an instance of ClassName
var factory = container.Resolve<Factory>(); // This is throwing the following exception.
var instance = factory(obj1Instance, "text"); // obj1Instance and "text" parameters cannot be determined at registration time.

异常堆栈跟踪：

Logging handled exception: Autofac.Core.DependencyResolutionException: Autofac.Core.DependencyResolutionException: An error occurred during the activation of a particular registration. See the inner exception for details. Registration: Activator = Factory (ReflectionActivator), Services = [ClassName+Factory], Lifetime = Autofac.Core.Lifetime.CurrentScopeLifetime, Sharing = None, Ownership = OwnedByLifetimeScope ---> None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'ClassName+Factory' can be invoked with the available services and parameters:
Cannot resolve parameter 'System.Object object' of constructor 'Void .ctor(System.Object, IntPtr)'. (See inner exception for details.) ---> Autofac.Core.DependencyResolutionException: None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'ClassName+Factory' can be invoked with the available services and parameters:
Cannot resolve parameter 'System.Object object' of constructor 'Void .ctor(System.Object, IntPtr)'.
   at Autofac.Core.Activators.Reflection.ReflectionActivator.GetValidConstructorBindings(IComponentContext context, IEnumerable`1 parameters)
   at Autofac.Core.Activators.Reflection.ReflectionActivator.ActivateInstance(IComponentContext context, IEnumerable`1 parameters)
   at Autofac.Core.Resolving.InstanceLookup.Activate(IEnumerable`1 parameters)
   --- End of inner exception stack trace ---
   at Autofac.Core.Resolving.InstanceLookup.Activate(IEnumerable`1 parameters)
   at Autofac.Core.Resolving.InstanceLookup.Execute()
   at Autofac.Core.Resolving.ResolveOperation.GetOrCreateInstance(ISharingLifetimeScope currentOperationScope, IComponentRegistration registration, IEnumerable`1 parameters)
   at Autofac.Core.Resolving.ResolveOperation.Execute(IComponentRegistration registration, IEnumerable`1 parameters)
   at Autofac.ResolutionExtensions.TryResolveService(IComponentContext context, Service service, IEnumerable`1 parameters, Object& instance)
   at Autofac.ResolutionExtensions.ResolveService(IComponentContext context, Service service, IEnumerable`1 parameters)
   at Autofac.ResolutionExtensions.Resolve[TService](IComponentContext context, IEnumerable`1 parameters)

Answer 1

您遇到的问题是您正在尝试注册工厂。 Autofac 了解如何解析委托，但不了解如何注册。

这应该可行：

public class ClassName
{
    public delegate ClassName Factory(Type1 obj1, string obj2);
    public ClassName(Type1 obj1, string obj2)
    {
        this.type1 = obj1;
        this.type2= obj2;
    }
}

// Registration 
container.RegisterType<ClassName>().AsSelf().InstancePerDependency();

// In some method to create an instance of ClassName
var factory = container.Resolve<ClassName.Factory>();
var instance = factory.Invoke(obj1Instance, "text");

---

编辑：

我自己运行后遇到了同样的异常，但很快意识到问题所在。引用autofac's entry on delegate factories我看到了这个：

Autofac默认将delegate的参数与构造函数的参数按名称匹配

我的构造函数参数的名称和我的委托参数的名称不匹配，这导致autofac 尝试按类型解析对象，因为你没有（除非你知道你想这样做，否则不应该这样做，即便如此，您也不应该）注册 string autofac 的 Autofac.Core.Activators.Reflection.DefaultConstructorFinder 失败。