Editing Mediator pattern (section)

=== C# ===
The mediator pattern ensures that components are [[loosely coupled]], such that they do not call each other explicitly, but instead do so through calls to a mediator. In the following example, the mediator registers all Components and then calls their {{Code|SetState}} methods.
<syntaxhighlight lang="csharp">
interface IComponent
{
    void SetState(object state);
}

class Component1 : IComponent
{
    internal void SetState(object state)
    {
        throw new NotImplementedException();
    }
}

class Component2 : IComponent
{
    internal void SetState(object state)
    {
        throw new NotImplementedException();
    }
}

// Mediates the common tasks
class Mediator
{
    internal IComponent Component1 { get; set; }
    internal IComponent Component2 { get; set; }

    internal void ChangeState(object state)
    {
        this.Component1.SetState(state);
        this.Component2.SetState(state);
    }
}
</syntaxhighlight>

A chat room could use the mediator pattern, or a system where many ‘clients’ each receive a message each time one of the other clients performs an action (for chat rooms, this would be when each person sends a message). In reality using the mediator pattern for a chat room would only be practical when used with [[remoting]]. Using raw sockets would not allow for the [[Delegation (object-oriented programming)|delegate]] [[callbacks]] (people subscribed to the Mediator class’ MessageReceived event).

<syntaxhighlight lang="csharp">
public delegate void MessageReceivedEventHandler(string message, string sender);

public class Mediator
{
    public event MessageReceivedEventHandler MessageReceived;

    public void Send(string message, string sender)
    {
        if (MessageReceived != null)
        {
            Console.WriteLine("Sending '{0}' from {1}", message, sender);
            MessageReceived(message, sender);
        }
    }
}

public class Person
{
    private Mediator _mediator;

    public Person(Mediator mediator, string name)
    {
        Name = name;
        _mediator = mediator;
        _mediator.MessageReceived += new MessageReceivedEventHandler(Receive);
    }

    public string Name { get; set; }

    private void Receive(string message, string sender)
    {
        if (sender != Name)
            Console.WriteLine("{0} received '{1}' from {2}", Name, message, sender);
    }

    public void Send(string message)
    {
        _mediator.Send(message, Name);
    }
}
</syntaxhighlight>