How to resolve dependency by using a named registertype in Unity?

Question

public interface IFoo {}

public interface IBar {}

public class Foo1 :  IFoo {}

public class FooOne : IFoo {}
public class FooTwo : IFoo {}

public class BarOne : IBar
{
    public BarOne(IFoo foo) {}        
} 

public class BarTwo : IBar
{
    public BarTwo(IFoo foo) {}        
} 

 class Program
{
    static void Main(string[] args)
    {
        UnityContainer container = new UnityContainer();
        container.RegisterType<IFoo, FooOne>("One")
            .RegisterType<IFoo, FooTwo>("Two")
            .RegisterType<IBar, BarOne>("One")
            .RegisterType<IFoo, BarTwo>("Two");                

        string fooType = "One";
        string barType = "Two";

        IFoo myFoo = container.Resolve<IFoo>(fooType);
        IBar myBar = container.Resolve<IBar>(barType);
    }
}

Code sample above throws this error :

Resolution of the dependency failed, type = "ConsoleApplication5.IBar", name = "Two". Exception occurred while: while resolving. Exception is: InvalidOperationException - The current type, ConsoleApplication5.IFoo, is an interface and cannot be constructed. Are you missing a type mapping? ----------------------------------------------- At the time of the exception, the container was:

Resolving ConsoleApplication5.BarTwo,Two (mapped from ConsoleApplication5.IBar, Two) Resolving parameter "foo" of constructor ConsoleApplication5.BarTwo(ConsoleApplication5.IFoo foo) Resolving ConsoleApplication5.IFoo,(none)

My solution is using DependencyResolver which changes this line:

IBar myBar = container.Resolve<IBar>(barType);

to this:

IBar myBar = container.Resolve<IBar>(barType, new DependencyOverride<IFoo>(myFoo));

I want to solve this issue using RegisterType method. Is it possible or is there any other solution?

Thanks.

Some details are missing. You need to register IMessageType with container somewhere in your code. — Tilak
@Tilak I edit the post. The error message was belonging to the original code. Now you can see the simplified version's error message. — Mehmet Kemal Bayer

Mark Mark · Accepted Answer · 2016-12-29T07:59:22

You have to determine which of your IFoo named registrations unity should use when your resolving an IBar.

container.RegisterType<IFoo, FooOne>("One")
         .RegisterType<IFoo, FooTwo>("Two")
         .RegisterType<IBar, BarOne>("One", new InjectionConstructor(
                                     new ResolvedParameter<IFoo>("One")))
         .RegisterType<IBar, BarTwo>("Two", new InjectionConstructor(
                                     new ResolvedParameter<IFoo>("Two")));

The Problem is that IFoo is twice registered by different implementations and unity does not know which one it should use when resolving that type.

How to resolve dependency by using a named registertype in Unity?

1 Answers