C# 责任链模式讲解和代码示例
责任链是一种行为设计模式， 允许你将请求沿着处理者链进行发送， 直至其中一个处理者对其进行处理。
该模式允许多个对象来对请求进行处理， 而无需让发送者类与具体接收者类相耦合。 链可在运行时由遵循标准处理者接口的任意处理者动态生成。
复杂度：
流行度：
使用示例： 责任链模式在 C# 程序中并不常见， 因为它仅在代码与对象链打交道时才能发挥作用。
识别方法： 该模式可通过一组对象的行为方法间接调用其他对象的相同方法来识别， 而且所有对象都会遵循相同的接口。
概念示例
本例说明了责任链设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
Program.cs: 概念示例
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); } } } Output.txt: 执行结果
Chain: Monkey > Squirrel > Dog Client: 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 > Dog Client: 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. 
