设计模式学习之路——Chain Of Responsibility 职责链模式
请求的发送者和接受者可能存在如下关系,某些对象的请求的接受者可能多种多样,变化无常,职责链(Chain Of Responsibility)模式允许多个类处理同一个请求,而不需要了解彼此的功能。它在类之间提供了一种松散的耦合:类之间唯一的联系就是相互传递的请求。请求在类之间传递,直到其中一个类处理它为止。
动机:
在软件构建过程中,一个请求可能被多个对象处理,但是每个请求在运行时只能有一个接受者,如果显式指定,将必不可少地带来请求发送者与接受者的紧耦合。
如何使请求的发送者不需要指定具体的接受者?让请求的接受者自己在运行时决定来处理请求,从而使两者解耦。
意图:
使多个对象都有机会处理请求,从而避免请求的发送者和接收者之间的耦合关系。将这些对象连成一条链,并沿着这条链传递请求,直到有一个对象处理它为止。
结构:
代码实现
using System; using System.Collections.Generic; using System.Text; namespace ChainOfResponsibility { class Program { static void Main(string[] args) { ClientSender client = new ClientSender(); BaseHandler SuTankHandler = new SuTank(null); BaseHandler USATankHandler = new USATank(SuTankHandler); BaseHandler SuFighterHandler = new SuFighter(USATankHandler); BaseHandler USAFighterHandler = new USAFighter(SuFighterHandler); client.Process(USAFighterHandler, Sender.SuFighter, Command.Attack); client.Process(USAFighterHandler, Sender.USATank, Command.Stop); Console.ReadKey(); } } /// <summary> /// /// </summary> public enum Command { Attack, //进攻 Stop //撤退 } public enum Sender { SuTank, //苏联坦克 USATank, //美国坦克 SuFighter, //苏联飞机 USAFighter //美国飞机 } public class Request { public Request(Command _cmd, Sender _sender) { this.cmd = _cmd; this.sender = _sender; } private Command cmd; public Command Cmd { get { return cmd; } set { cmd = value; } } private Sender sender; public Sender Sender { get { return sender; } set { sender = value; } } } public abstract class BaseHandler { public BaseHandler(BaseHandler _next) { this.Next = _next; } protected abstract bool CanHandlerRequest(Request request); public virtual void HandlerRequest(Request request) { if (this.next != null) { this.next.HandlerRequest(request); } } private BaseHandler next; public BaseHandler Next { get { return this.next; } set { this.next = value; } } } public class SuTank : BaseHandler { public SuTank(BaseHandler next) : base(next) { } protected override bool CanHandlerRequest(Request request) { if (request.Sender == Sender.SuTank) { return true; } else { return false; } } public override void HandlerRequest(Request request) { if (this.CanHandlerRequest(request)) { if (request.Cmd == Command.Attack) { Console.WriteLine("Su坦克进攻!"); } else if (request.Cmd == Command.Stop) { Console.WriteLine("Su坦克撤退!"); } } else { base.HandlerRequest(request); } } } public class SuFighter : BaseHandler { public SuFighter(BaseHandler next) : base(next) { } protected override bool CanHandlerRequest(Request request) { if (request.Sender == Sender.SuFighter) { return true; } else { return false; } } public override void HandlerRequest(Request request) { if (this.CanHandlerRequest(request)) { if (request.Cmd == Command.Attack) { Console.WriteLine("Su飞机进攻!"); } else if (request.Cmd == Command.Stop) { Console.WriteLine("Su飞机撤退!"); } } else { base.HandlerRequest(request); } } } public class USATank : BaseHandler { public USATank(BaseHandler next) : base(next) { } protected override bool CanHandlerRequest(Request request) { if (request.Sender == Sender.USATank) { return true; } else { return false; } } public override void HandlerRequest(Request request) { if (this.CanHandlerRequest(request)) { if (request.Cmd == Command.Attack) { Console.WriteLine("USA坦克进攻!"); } else if (request.Cmd == Command.Stop) { Console.WriteLine("USA坦克撤退!"); } } else { base.HandlerRequest(request); } } } public class USAFighter : BaseHandler { public USAFighter(BaseHandler next) : base(next) { } protected override bool CanHandlerRequest(Request request) { if (request.Sender == Sender.USAFighter) { return true; } else { return false; } } public override void HandlerRequest(Request request) { if (this.CanHandlerRequest(request)) { if (request.Cmd == Command.Attack) { Console.WriteLine("USA飞机进攻!"); } else if (request.Cmd == Command.Stop) { Console.WriteLine("USA飞机撤退!"); } } else { base.HandlerRequest(request); } } } public class ClientSender { public void Process(BaseHandler handler, Sender sender,Command cmd) { Request request = new Request(cmd, sender); handler.HandlerRequest(request); } } }
Chain of Responsibility模式的几个要点
1.Chain of Responsibility 模式的应用场合在于“一个请求可能有多个接受者,但是最后真正的接受者只有一个”,只有这时候请求发送者与接受者的耦合才有可能出现“变化脆弱”的症状,职责链的目的就是将二者解耦,从而更好地应对变化。
3.应用了Chain of Responsibility 模式后,对象的职责分派将更具灵活性。我们可以在运行时动态添加/修改请求的处理职责。
4.如果请求传递到职责链的末尾仍得不到处理,应该有一个合理的缺省机制。这也是每一个接受对象的责任,而不是发出请求的对象的责任