Unity .NET: List of dependencies

Question

Is it possible to inject a list of dependencies like this in Unity or other kind of IoC libraries?

public class Crawler 
{
    public Crawler(IEnumerable<IParser> parsers) 
    {
         // init here...
    }
}

In this way I can register multiple IParser in my container and then resolve them.

Is it possible? Thanks

Answer 1

It is possible but you need to apply some workarounds. First you need to register each IParser with a name in the Unity Container. Second you need to register a mapping from IParser[] to IEnumerable<IParser> in the container. Otherwise the container cannot inject the parsers to the constructor. Here´s how i have done it before.

IUnityContainer container = new UnityContainer();

container.RegisterType<IParser, SuperParser>("SuperParser");
container.RegisterType<IParser, DefaultParser>("DefaultParser");
container.RegisterType<IParser, BasicParser>("BasicParser");
container.RegisterType<IEnumerable<IParser>, IParser[]>();
container.RegisterType<Crawler>();

Crawler crawler = container.Resolve<Crawler>();

I have discarded this solution by introducing a factory, that encapsulates unity to construct the needed types. Here´s how i would do it in your case.

public interface IParserFactory{
  IEnumerable<IParser> BuildParsers();
}

public class UnityParserFactory : IParserFactory {
  private IUnityContainer _container;

  public UnityParserFactory(IUnityContainer container){
    _container = container;
  }

  public IEnumerable<IParser> BuildParsers() {
    return _container.ResolveAll<IParser>();
  }
}

public class Crawler {
  public Crawler(IParserFactory parserFactory) {
     // init here...
  }
}

With this you can register the types as follows:

IUnityContainer container = new UnityContainer();

container.RegisterType<IParser, SuperParser>();
container.RegisterType<IParser, DefaultParser>();
container.RegisterType<IParser, BasicParser>();
container.RegisterType<IParserFactory, UnityParserFactory>();

Crawler crawler = container.Resolve<Crawler>();