Unity - Inject an object to Constructor by calling a Method of a Class

Question

I have the following interface and its implementation

public class DummyProxy : IDummyProxy
{
    public string SessionID { get; set; }
    public DummyProxy(string sessionId)
    {
        SessionId = sessionId;
    }
}

public interface IDummyProxy
{
}

Then I have another class to get a session id

public class DummySession
{
    public string GetSessionId()
    {
        Random random = new Random();
        return random.Next(0, 100).ToString();
    }
}

Now, in my Unity container, I would like to inject 'session id' to DummyProxy every time the container is trying to resolve IDummyProxy. But this 'session id' must be generated from DummySession class.

container.RegisterType<IDummyProxy, DummyProxy>(
    new InjectionConstructor(new DummySession().GetSessionId()));

Is this even possible?

Answer 1

Your best approach for this would be to make use of an InjectionFactory, i.e.

container.RegisterType<IDummyProxy, DummyProxy>(new InjectionFactory(c => 
{
    var session = c.Resolve<DummySession>() // Ideally this would be IDummySession
    var sessionId = session.GetSessionId();

    return new DummyProxy(sessionId);
}));

An InjectionFactory allows you to execute additional code when creating the instance.

The c is the IUnityContainer being used to perform the resolve, we use this to resolve the session and then obtain the session id, from that you can then create your DummyProxy instance.