Phil Sandler Phil Sandler - 1 month ago 4
C# Question

Automatically Registering All Implementations of a Generic Interface

My current registration code:

Assembly web = Assembly.Load("MyAssembly");
types.AddRange(web.GetTypes());
//etc.

foreach (var theInterface in types.Where(t => t.IsInterface))
{
var assignableType = types.Where(t => theInterface.IsAssignableFrom(t) && t != theInterface);
foreach (var type in assignableType)
{
container.RegisterType(theInterface, type);
}
}


My generic interface and its implementations:

public interface IDomainEventHandler<in T>
{
void Handle(T message);
}

public class DomainEventHandler1 : IDomainEventHandler<PhilTest1>
{
public void Handle(PhilTest1 message)
{
throw new System.NotImplementedException();
}
}

public class DomainEventHandler2 : IDomainEventHandler<PhilTest2>
{
public void Handle(PhilTest2 message)
{
throw new System.NotImplementedException();
}
}

public class DomainEventHandler3 : IDomainEventHandler<PhilTest2>
{
public void Handle(PhilTest2 message)
{
throw new System.NotImplementedException();
}
}

public class PhilTest1
{

}

public class PhilTest2
{

}


Here is a simplified version of how I would resolve:

IEnumerable<IDomainEventHandler<PhilTest2>> listeners = Container.ResolveAll<IDomainEventHandler<PhilTest2>>();
IEnumerable<IDomainEventHandler<PhilTest1>> listeners2 = Container.ResolveAll<IDomainEventHandler<PhilTest1>>();


This doesn't work--listeners and listeners2 are both empty after resolving. This is not unexpected.

In Windsor, I could do something like this:

container.Register(AllTypes.FromAssemblyNamed("MyAssembly").BasedOn(typeof(IDomainEventHandler<>)).WithService.Base());


How would I register all instances of IDomainEventHandler in Unity? I'd prefer to keep the existing registration code intact (if possible).

Answer

A bit painful, but I finally pieced it together via googling and debugging:

Registration:

    IEnumerable<Type> handlers = types.Where(t => IsAssignableToGenericType(t, typeof(IDomainEventHandler<>)) && !t.IsInterface);

    foreach (var handler in handlers)
    {
        container.AddNewExtension<OpenGenericExtension>()
                    .Configure<IOpenGenericExtension>()
                    .RegisterClosedImpl(typeof (IDomainEventHandler<>), handler);
    }

IsAssignableToGenericType method:

    private static bool IsAssignableToGenericType(Type givenType, Type genericType)
    {
        var interfaceTypes = givenType.GetInterfaces();

        foreach (var it in interfaceTypes)
        {
            if (it.IsGenericType && it.GetGenericTypeDefinition() == genericType)
                return true;
        }

        if (givenType.IsGenericType && givenType.GetGenericTypeDefinition() == genericType)
            return true;

        Type baseType = givenType.BaseType;
        if (baseType == null) return false;

        return IsAssignableToGenericType(baseType, genericType);
    }

And the Extension. Note that if I didn't use a name for the registration, only one type would remain registered. I believe this is by design?

public interface IOpenGenericExtension : IUnityContainerExtensionConfigurator
{
    void RegisterClosedImpl(Type openGenericInterface, Type closedType);
}

public class OpenGenericExtension : UnityContainerExtension, IOpenGenericExtension
{
    protected override void Initialize() {}

    public void RegisterClosedImpl(Type openGenericInterface, Type closedType)
    {
        closedType.GetInterfaces().Where(x => x.IsGenericType)
                  .Where(x => x.GetGenericTypeDefinition() == openGenericInterface)
                  .ToList()
                  .ForEach(x => Container.RegisterType(x, closedType, closedType.Name));
    }
}
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