How do I pass a parameter to a component in the middle of a resolve chain?

There are times when you need to resolve a service that consumes a component somewhere down its dependency chain and that component needs a parameter passed to it.

For this question, let’s imagine a simple email notification system like this:

// This interface lets you send an email notification to someone.
public interface INotifier
  void Send(string address, string message);

// This implementation of the notifier uses a backing email
// repository for doing the heavy lifting.
public class Notifier : INotifier
  private IEmailServer _server;
  public Notifier(IEmailServer server)
    this._server = server;

  public void Send(string address, string message)
    this._server.SendMessage(address, "", message);

// This email server interface is what the notifier will use
// to send the email.
public interface IEmailServer
  void SendMessage(string toAddress, string fromAddress, message);

// Notice this implementation takes a string parameter for the server address -
// something we won't know until runtime so we can't explicitly register the
// parameter value.
public class EmailServer : IEmailServer
  private string _serverAddress;
  public EmailServer(string serverAddress)
    this._serverAddress = serverAddress;

  public void SendMessage(string toAddress, string fromAddress, message)
    // ...send the message through the specified server address.

When you register things in Autofac, you might have registrations that look like this:

var builder = new ContainerBuilder();
var container = builder.Build();

The only time you know the email server address is at runtime - maybe through a context or environment parameter, maybe through configuration.

How do you pass a parameter to the email server when you resolve the notifier?

Why This is a Design Problem

Before answering the question, consider that in many respects that asking this question indicates a sort of design problem.

Technically speaking, you’re resolving an INotifier - a component that doesn’t need to know about the runtime parameter with the email server address. The implementation of that INotifier could change. You could register a stub for testing, or switch up how emails get sent so they no longer need to know about the address.

Passing the server address as a parameter to the INotifier breaks the decoupling that interface-based development and inversion of control gives you by assuming that you “know” how the entire dependency chain is being resolved.

The key to solving the problem is to break that “knowledge” so you’re not passing a parameter.


Instead of trying to pass a parameter, flip the problem around - figure out how you determine the parameter at runtime and wrap that in a provider or a lambda expression registration.

This changes the question to a different FAQ where we walk through answers step by step: How do I inject configuration, environment, or context parameters?