Autofac和RegisterGeneric-限制允许的泛型

Question

Let's say that I have a generic registration with Autofac:

builder.RegisterGeneric(typeof(Injectator<>))
       .As(typeof(IInjectator<>))
       .SingleInstance();

Now (I)Injectator has single generic. But I don't want every possible class or struct to be allowed as generic.

I only want it for classes, that inherit from some specified class:

class JustClass { // not allowed
}

class SpecialClass : InjectableClass { // allowed
}

Answer 1

The easiest way would be to add a constraint on your generic interface :

public interface IInjectator<T> 
    where T : InjectableClass 
{ }

This way .net won't allow you to get an invalid type.

If you can't do this, there is no easy way to change the behavior of RegisterGeneric one way I can see is to subscribe to the OnActivated event and throw an exception :

builder.RegisterGeneric(typeof(Foo<>))
        .As(typeof(IFoo<>))
        .OnActivated(e =>
        {
            Boolean isValid = e.Component.Services
                .OfType<IServiceWithType>()
                .Where(s => s.ServiceType.IsConstructedGenericType
                            && s.ServiceType.GetGenericTypeDefinition() == typeof(IFoo<>)
                            && s.ServiceType.GetGenericArguments()[0].IsAssignableTo<IBar>())
                .Any();

            if (!isValid)
            {
                throw new Exception("boom");
            }
        });

If you don't want to throw an exception you can implement your own IRegistrationSource . You can have a look at the source code of the native OpenGenericRegistrationSource which resolves open generic types.