设计模式之职责链模式

结构

职责链模式

说明

This pattern avoids coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. It chains the receiving objects and passes the request along the chain until an object handles it.

使多个对象都有机会处理请求，从而避免了请求的发送者与接收者之间的耦合。将接收对象组成链，在链上传递请求，直到有一个对象处理请求为止。

适用条件

有多个对象可以处理一个请求，具体由哪个对象处理在运行时确定；
在不明确接收者的情况下，向多个对象发送请求；
可处理请求的对象的集合应被动态指定。

实现

class Client {
        
    static void Main(string[] args) {
        Handler handlerChain = new ConcreteHandler1(new ConcreteHandler2(null));

        Request request1 = new ConcreteRequest1();
        handlerChain.HandleRequest(request1);

        Request request2 = new ConcreteRequest2();
        handlerChain.HandleRequest(request2);

        Console.ReadKey();
    }
}

public abstract class Handler {

    private readonly Handler _successor;

    protected Handler(Handler successor) {
        this._successor = successor;
    }

    protected Handler Successor {
        get {
            return this._successor;
        }
    }

    public abstract void HandleRequest(Request request);

}

public class ConcreteHandler1 : Handler {
        
    public ConcreteHandler1(Handler successor) : base(successor) {
    }

    public override void HandleRequest(Request request) {
        if (request is ConcreteRequest1) {
            Console.WriteLine("ConcreteRequest1 is handled by ConcreteHandler1");
        }
        else {
            this.Successor.HandleRequest(request);
        }
    }
}

public class ConcreteHandler2 : Handler {

    public ConcreteHandler2(Handler successor) : base(successor) {
    }

    public override void HandleRequest(Request request) {
        if (request is ConcreteRequest2) {
            Console.WriteLine("ConcreteRequest2 is handled by ConcreteHandler2");
        }
        else {
            this.Successor.HandleRequest(request);
        }
    }
}

public abstract class Request {
}

public class ConcreteRequest1 : Request {
}

public class ConcreteRequest2 : Request {

}

设计模式概述

设计模式之命令模式