设计模式（16）中介者模式

模式介绍

中介器设计模式定义了一个对象，该对象封装了一组对象之间如何相互作用。

示例

我们想象一下电影院的快餐柜，电影院有多个区域都有这样的快餐柜，我们来设计一个它们之间交流的系统。

中介者接口：

/// <summary>
/// The Mediator interface, which defines a send message method which the concrete mediators must implement.
/// </summary>
interface Mediator
{
    void SendMessage(string message, ConcessionStand concessionStand);
}

抽象的柜台：

/// <summary>
/// The Colleague abstract class, representing an entity involved in the conversation which should receive messages.
/// </summary>
abstract class ConcessionStand
{
    protected Mediator mediator;

    public ConcessionStand(Mediator mediator)
    {
        this.mediator = mediator;
    }
}

具体的柜台：

/// <summary>
/// A Concrete Colleague class
/// </summary>
class NorthConcessionStand : ConcessionStand
{
    // Constructor
    public NorthConcessionStand(Mediator mediator) : base(mediator)
    {
    }

    public void Send(string message)
    {
        Console.WriteLine("North Concession Stand sends message: " + message);
        mediator.SendMessage(message, this);
    }

    public void Notify(string message)
    {
        Console.WriteLine("North Concession Stand gets message: "  + message);
    }
}

/// <summary>
/// A Concrete Colleague class
/// </summary>
class SouthConcessionStand : ConcessionStand
{
    public SouthConcessionStand(Mediator mediator) : base(mediator)
    {
    }

    public void Send(string message)
    {
        Console.WriteLine("South Concession Stand sends message: " + message);
        mediator.SendMessage(message, this);
    }

    public void Notify(string message)
    {
        Console.WriteLine("South Concession Stand gets message: " + message);
    }
}

具体的中介者：

/// <summary>
/// The Concrete Mediator class, which implement the send message method and keep track of all participants in the conversation.
/// </summary>
class ConcessionsMediator : Mediator
{
    private NorthConcessionStand _northConcessions;
    private SouthConcessionStand _southConcessions;

    public NorthConcessionStand NorthConcessions
    {
        set { _northConcessions = value; }
    }

    public SouthConcessionStand SouthConcessions
    {
        set { _southConcessions = value; }
    }

    public void SendMessage(string message, ConcessionStand colleague)
    {
        if (colleague == _northConcessions)
        {
            _southConcessions.Notify(message);
        }
        else
        {
            _northConcessions.Notify(message);
        }
    }
}

客户端调用：

static void Main(string[] args)
{
    ConcessionsMediator mediator = new ConcessionsMediator();

    NorthConcessionStand leftKitchen = new NorthConcessionStand(mediator);
    SouthConcessionStand rightKitchen = new SouthConcessionStand(mediator);

    mediator.NorthConcessions = leftKitchen;
    mediator.SouthConcessions = rightKitchen;

    leftKitchen.Send("Can you send some popcorn?");
    rightKitchen.Send("Sure thing, Kenny's on his way.");

    rightKitchen.Send("Do you have any extra hot dogs?  We've had a rush on them over here.");
    leftKitchen.Send("Just a couple, we'll send Kenny back with them.");

    Console.ReadKey();
}

总结

中介者使中介人“站在”通信对象之间，控制他们的通信。常用于聊天系统。

源代码

https://github.com/exceptionnotfound/DesignPatterns/tree/master/Mediator

原文

https://www.exceptionnotfound.net/mediator-the-daily-design-pattern/