Mediator C# Implementation

Colleague.cs

// Colleague only exposes Notify method
// SetMediator and HandleNotification are private and protected to simplify client interface
// Not public methods are invoked using reflection.

public abstract class Colleague
{
    private IMediator _mediator;


    protected void SetMediator(IMediator mediator)
    {
        _mediator = mediator;
    }

    protected abstract void HandleNotification(string message);

    public void Notify(string message)
    {
        _mediator.Notify(message, this);
    }
}

Colleague1.cs

public class Colleague1 : Colleague
{
    protected override void HandleNotification(string message)
    {
        Console.WriteLine($"{nameof(Colleague1)}: {message}");
    }
}

Colleague2.cs

public class Colleague2 : Colleague
{
    protected override void HandleNotification(string message)
    {
        Console.WriteLine($"{nameof(Colleague2)}: {message}");
    }
}

IMediator.cs

public interface IMediator
{
    void Notify(string message, Colleague colleague);
}

Mediator.cs

public class Mediator: IMediator
{
    private readonly List<Colleague> _colleagues = new List<Colleague>();

    public Colleague CreateColleague<T>() where T : Colleague, new()
    {
        var colleague = new T();
        CallColleagueNoPublicMethod(colleague, "SetMediator", this);

        _colleagues.Add(colleague);
        return colleague;
    }

    public void Notify(string message, Colleague colleague)
    {
        var instance = _colleagues.FirstOrDefault(e => e == colleague);
        CallColleagueNoPublicMethod(instance, "HandleNotification", message);
    }

    private static void CallColleagueNoPublicMethod(Colleague instance, string methodName, object parameter)
    {
        var method = instance.GetType().GetMethod(
            methodName,
            BindingFlags.NonPublic |
            BindingFlags.Instance
        );

        method!.Invoke(instance, new[] { parameter });
    }
}