使用autofac解析在运行时在构造函数中使用参数的类实例

Question

I'm following below example to create a class instance at runtime using autofac. http://autofaccn.readthedocs.io/en/latest/advanced/delegate-factories.html

But when running locally, I'm seeing an exception. I'm very new to autofac and let me know if I'm doing anything wrong here or if you need any more information.

Code structure:

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.

The exception stackTrace:

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

The problem you have is that you're trying to register a factory. Autofac understands how to resolve a delegate, but it doesn't understand how to register it.

This should work:

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");

---

Edit:

After running this myself I got the same exception but quickly realised what the issue was. Quoting autofac's entry on delegate factories I saw this:

By default, Autofac matches the parameters of the delegate to the parameters of the constructor by name

The names of my constructor's parameters and my delegates' parameters didn't match which leads autofac to try and resolve the object by type, and since you haven't (and shouldn't unless you know you want to, and even so, you shouldn't) registered a string autofac 's Autofac.Core.Activators.Reflection.DefaultConstructorFinder fails.