责任链模式(ChainOfResponsibility)

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using System;using System.Collections.Generic;namespace RefactoringGuru.DesignPatterns.ChainOfResponsibility.Conceptual{ // The Handler interface declares a method for building the chain of // handlers. It also declares a method for executing a request. public interface IHandler { IHandler SetNext(IHandler handler); object Handle(object request); } // The default chaining behavior can be implemented inside a base handler // class. abstract class AbstractHandler : IHandler { private IHandler _nextHandler; public IHandler SetNext(IHandler handler) { this._nextHandler = handler; // Returning a handler from here will let us link handlers in a // convenient way like this: // monkey.SetNext(squirrel).SetNext(dog); return handler; } public virtual object Handle(object request) { if (this._nextHandler != null) { return this._nextHandler.Handle(request); } else { return null; } } } class MonkeyHandler : AbstractHandler { public override object Handle(object request) { if ((request as string) == "Banana") { return $"Monkey: I'll eat the {request.ToString()}.\n"; } else { return base.Handle(request); } } } class SquirrelHandler : AbstractHandler { public override object Handle(object request) { if (request.ToString() == "Nut") { return $"Squirrel: I'll eat the {request.ToString()}.\n"; } else { return base.Handle(request); } } } class DogHandler : AbstractHandler { public override object Handle(object request) { if (request.ToString() == "MeatBall") { return $"Dog: I'll eat the {request.ToString()}.\n"; } else { return base.Handle(request); } } } class Client { // The client code is usually suited to work with a single handler. In // most cases, it is not even aware that the handler is part of a chain. public static void ClientCode(AbstractHandler handler) { foreach (var food in new List<string> { "Nut", "Banana", "Cup of coffee" }) { Console.WriteLine($"Client: Who wants a {food}?"); var result = handler.Handle(food); if (result != null) { Console.Write($" {result}"); } else { Console.WriteLine($" {food} was left untouched."); } } } } class Program { static void Main(string[] args) { // The other part of the client code constructs the actual chain. var monkey = new MonkeyHandler(); var squirrel = new SquirrelHandler(); var dog = new DogHandler(); monkey.SetNext(squirrel).SetNext(dog); // The client should be able to send a request to any handler, not // just the first one in the chain. Console.WriteLine("Chain: Monkey > Squirrel > Dog\n"); Client.ClientCode(monkey); Console.WriteLine(); Console.WriteLine("Subchain: Squirrel > Dog\n"); Client.ClientCode(squirrel); } }}

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Chain: Monkey > Squirrel > DogClient: Who wants a Nut? Squirrel: I'll eat the Nut.Client: Who wants a Banana? Monkey: I'll eat the Banana.Client: Who wants a Cup of coffee? Cup of coffee was left untouched.Subchain: Squirrel > DogClient: Who wants a Nut? Squirrel: I'll eat the Nut.Client: Who wants a Banana? Banana was left untouched.Client: Who wants a Cup of coffee? Cup of coffee was left untouched.