Properties (PropertiesAutowired) are not injected when using generics<T>

Question

First, let's take a look in the code:

using System;
using Autofac;

namespace PropertyInjectionAutofacPoC
{
    public interface IInterfaceA { }
    public interface IInterfaceB
    {
        IInterfaceA ClassA { get; set; }
    }

    public class ClassA : IInterfaceA { }
    public class ClassB : IInterfaceB
    {
        public IInterfaceA ClassA { get; set; } // this is injected properly //
    }

    public class Z { }

    public interface IInterfaceC<T> { }
    public interface IInterfaceD<T>
    {
        IInterfaceA ClassA { get; set; }
        IInterfaceC<T> ClassC { get; set; }
    }

    public interface IInterfaceCZ : IInterfaceC<Z> { }

    public abstract class ClassD<T> : IInterfaceD<T>
    {
        public IInterfaceA ClassA { get; set; } // this is not injected, it's always null //
        public IInterfaceC<T> ClassC { get; set; } // this is not injected, it's always null //
    }

    public abstract class ClassC<T> : IInterfaceC<T> { }
    public sealed class ClassCZ : ClassC<Z>, IInterfaceCZ { }

    public interface IRepositoryZ : IInterfaceD<Z> { }
    public sealed class RepositoryZ : ClassD<Z>, IRepositoryZ { }

    internal class Program
    {
        private static IContainer _container;

        private static void Main()
        {
            try
            {
                RegisterServices();

                // it works //
                 var a = _container.Resolve<IInterfaceB>();

                 // it doesn't work //
                 var b = _container.Resolve<IRepositoryZ>(); // ClassC property is null
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }
            finally
            {
                DisposeServices();
            }
        }

        private static void RegisterServices()
        {
            var builder = new ContainerBuilder();

            builder.RegisterType<ClassA>().As<IInterfaceA>();
            builder.RegisterType<ClassB>().As<IInterfaceB>().PropertiesAutowired(); // works like a charm //

            builder.RegisterGeneric(typeof(ClassC<>)).As(typeof(IInterfaceC<>)).PropertiesAutowired();
            builder.RegisterGeneric(typeof(ClassD<>)).As(typeof(IInterfaceD<>)).PropertiesAutowired(); // it doesn't work //

            builder.RegisterType<ClassCZ>().As<IInterfaceCZ>();
            builder.RegisterType<RepositoryZ>().As<IRepositoryZ>();

            _container = builder.Build();
        }

        private static void DisposeServices()
        {
            if (_container != null &&
                _container is IDisposable disposable)
                disposable.Dispose();
        }
    }


}

If I change everything to constructors, it works perfectly like a charm but, the main idea for using injected properties here is to avoid the constructor hell.

In the code snippet above, there's some comments where I mentioned what works and what doesn't. The properties injection works properly when there's no generics in use.

So, I'm asking you guys, what am I doing wrong here and what my code is missing to work?

Thanks so much!

Answer 1

The problem you have here is mostly about where you've specified PropertiesAutowired vs what you are resolving.

I've updated your RegisterServices method with some additional comments.

private static void RegisterServices()
{
    var builder = new ContainerBuilder();

    builder.RegisterType<ClassA>().As<IInterfaceA>();
    builder.RegisterType<ClassB>().As<IInterfaceB>().PropertiesAutowired();

    // These registrations aren't really valid. You would never be able to
    // resolve IInterfaceC<> or IInterfaceD<>, because they are abstract classes, so cannot be constructed.
    // You'll always get a NoConstructorsFoundException.
    builder.RegisterGeneric(typeof(ClassC<>)).As(typeof(IInterfaceC<>)).PropertiesAutowired();
    builder.RegisterGeneric(typeof(ClassD<>)).As(typeof(IInterfaceD<>)).PropertiesAutowired();

    builder.RegisterType<ClassCZ>().As<IInterfaceCZ>();

    // When I resolve IRepositoryZ, this is the registration that gets provided. So this is where you need PropertiesAutowired.
    // Just because RepositoryZ derives from ClassD<Z> does not mean it inherits any of its component registration information,
    // which I think is what you may have been expecting.
    //
    // However, the resolve of IRepositoryZ will now throw a NoConstructorFoundException, because when it goes to inject IInterfaceC<Z>
    // onto the property, it hits the invalid registration problem above.
    builder.RegisterType<RepositoryZ>().As<IRepositoryZ>().PropertiesAutowired();

    _container = builder.Build();
}

Fundamentally, I think you may need to rejig some of your generic class vs concrete class inheritance. I don't think there's a straightforward way to make a generic service be supplied by a concrete registration as you have tried to do here.