Mediator Pattern

Mediator Pattern 

Gamma Categorization: Behavioral Design Pattern
Summary: Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Sample Code

Problem: We want to apply several commands on the digital camera.

Code

public class Person

{

    public string Name;

    public ChatRoom Room;

    private List<string> chatLog = new List<string>();

    public Person(string name)

    {

        Name = name;

    }

    public void Receive(string sender, string message)

    {

        string s = $"{sender}: '{message}'";

        System.Console.WriteLine($"[{Name}'s chat session] {s}");

        chatLog.Add(s);

    }

    public void Say(string message)

    {

        Room.Broadcast(Name, message);

    }

    public void PrivateMessage(string who, string message)

    {

        Room.Message(Name, who, message);

    }

}

public class ChatRoom

{

    private List<Person> people = new List<Person>();

    public void Broadcast(string source, string message)

    {

        foreach (var p in people)

            if (p.Name != source)

                p.Receive(source, message);

    }

    public void Join(Person p)

    {

        string joinMsg = $"{p.Name} joins the chat";

        Broadcast("room", joinMsg);

        p.Room = this;

        people.Add(p);

    }

    public void Message(string source, string destination, string message)

    {

        people.FirstOrDefault(p => p.Name == destination)?.Receive(source, message);

    }

}

Usage

var room = new ChatRoom();

var admin = new Person("Admin");

var user1 = new Person("User1");

var user2 = new Person("User2");

room.Join(admin);

room.Join(user1);

room.Join(user2);

user1.Say("hi room");

user2.Say("oh, hey user1");

var guru = new Person("guru");

room.Join(guru);

guru.Say("hi everyone!");

user1.PrivateMessage("guru", "I need some info...");

Output

[Admin's chat session] room: 'User1 joins the chat'
[Admin's chat session] room: 'User2 joins the chat'
[User1's chat session] room: 'User2 joins the chat'
[Admin's chat session] User1: 'hi room'
[User2's chat session] User1: 'hi room'
[Admin's chat session] User2: 'oh, hey user1'
[User1's chat session] User2: 'oh, hey user1'
[Admin's chat session] room: 'guru joins the chat'
[User1's chat session] room: 'guru joins the chat'
[User2's chat session] room: 'guru joins the chat'
[Admin's chat session] guru: 'hi everyone!'
[User1's chat session] guru: 'hi everyone!'
[User2's chat session] guru: 'hi everyone!'
[guru's chat session] User1: 'I need some info...'