ChainOfResponsibilityPattern-责任链模式

在C#中，责任链模式（Chain of Responsibility Pattern）是一种行为型设计模式，它可让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。请求沿着一个链传递，直到有一个对象处理它为止。

责任链模式有以下几个关键角色：

Handler（处理器）：定义处理请求的接口，并通常持有一个指向下一个处理器的引用。

ConcreteHandler（具体处理器）：实现处理请求的接口，并决定是否能够处理该请求，如果不能处理则将请求传递给下一个处理器。

下面是一个示例，展示如何在C#中使用责任链模式来实现一个简单的请假审批系统：

namespace ChainOfResponsibilityPattern_责任链模式
{
    public class ChainOfResponsibility
    {
        public abstract class LeaveRequestHandler
        {
            protected LeaveRequestHandler NextHandler;

            public void SetNextHandler(LeaveRequestHandler nextHandler)
            {
                NextHandler = nextHandler;
            }

            public abstract void HandleRequest(LeaveRequest request);
        }
        // ConcreteHandler
        public class SupervisorHandler : LeaveRequestHandler
        {
            public override void HandleRequest(LeaveRequest request)
            {
                if (request.Days <= 3)
                {
                    Console.WriteLine("Leave request approved by supervisor");
                }
                else if (NextHandler != null)
                {
                    NextHandler.HandleRequest(request);
                }
            }
        }
        public class ManagerHandler : LeaveRequestHandler
        {
            public override void HandleRequest(LeaveRequest request)
            {
                if (request.Days <= 5)
                {
                    Console.WriteLine("Leave request approved by manager");
                }
                else if (NextHandler != null)
                {
                    NextHandler.HandleRequest(request);
                }
            }
        }
        public class HRHandler : LeaveRequestHandler
        {
            public override void HandleRequest(LeaveRequest request)
            {
                if (request.Days <= 7)
                {
                    Console.WriteLine("Leave request approved by HR");
                }
                else
                {
                    Console.WriteLine("Leave request denied");
                }
            }
        }
        // LeaveRequest
        public class LeaveRequest
        {
            public int Days { get; set; }
        }

    }
}

namespace ChainOfResponsibilityPattern_责任链模式
{
    internal class Program
    {
        static void Main(string[] args)
        {
            LeaveRequestHandler supervisor = new SupervisorHandler();
            LeaveRequestHandler manager = new ManagerHandler();
            LeaveRequestHandler hr = new HRHandler();

            supervisor.SetNextHandler(manager);
            manager.SetNextHandler(hr);

            LeaveRequest request = new LeaveRequest { Days = 2 };
            supervisor.HandleRequest(request);

            request = new LeaveRequest { Days = 6 };
            supervisor.HandleRequest(request);

            request = new LeaveRequest { Days = 10 };
            supervisor.HandleRequest(request);

            Console.Read();

            //输出结果
            //Leave request approved by supervisor
            //Leave request approved by HR
            //Leave request denied
        }
    }
}

通过使用责任链模式，可以让多个对象都有机会处理请求，避免请求发送者和接收者之间的紧耦合关系。可以根据实际需求创建不同的责任链，并按照顺序进行处理。此外，责任链模式还具有灵活性，可以动态地改变链中的处理顺序或添加新的处理器。