Unity resolving constructor with ICollection<IMyInterface> dependency

Question

I'm programming a rule engine. I have an interface IRule which many rules implement. Additionally, I have a RuleExecutor which get an IEnumerable<IRule> dependency injected.

I want Unity to inject an IEnumerable<IRule> with all bound implementations, but it doesn't work unfortunately.

This is my configuration:

container.RegisterType<IRule, RuleA>("a");
container.RegisterType<IRule, RuleB>("b");
container.RegisterType<IRule, RuleC>("c");
container.RegisterType<IRule, RuleD>("d");
container.RegisterType<IRule, RuleE>("e");
container.RegisterCollection<IRule>();

container.RegisterType<IRuleExecutor, RuleExecutor>(new InjectionConstructor(typeof(IEnumerable<IRule>)));

RegisterCollection is this:

public static class UnityExtensions
{
    public static void RegisterCollection<T>(this IUnityContainer container) where T : class
    {
        container.RegisterType<IEnumerable<T>>(new InjectionFactory(c => c.ResolveAll<T>()));
    }
}

I get following exception message when resolving:

RuleExecutor does not have a constructor that takes the parameters ().

How is this possible with Unity?

NightOwl888 NightOwl888 · Accepted Answer · 2018-03-07T13:07:35

Unity will inject all named instances into an IEnumerable<T> automatically. Here is a working example.

using System.Collections.Generic;
using Unity;

class Program
{
    static void Main(string[] args)
    {
        var container = new UnityContainer();

        container.RegisterType<IRule, RuleA>("a");
        container.RegisterType<IRule, RuleB>("b");
        container.RegisterType<IRule, RuleC>("c");
        container.RegisterType<IRule, RuleD>("d");
        container.RegisterType<IRule, RuleE>("e");
        container.RegisterType<IRuleExecutor, RuleExecutor>();

        var executor = container.Resolve<IRuleExecutor>();
    }
}

public interface IRule { }
public class RuleA : IRule { }
public class RuleB : IRule { }
public class RuleC : IRule { }
public class RuleD : IRule { }
public class RuleE : IRule { }

public interface IRuleExecutor { }
public class RuleExecutor : IRuleExecutor
{
    public RuleExecutor(IEnumerable<IRule> rules)
    {
        // Rules RuleA through RuleE are injected here...
    }
}

Unity resolving constructor with ICollection<IMyInterface> dependency

1 Answers