呼叫中心升级摘录，使用责任链模式

Question

这是我在网上发现的一次编码面试，要在30分钟内解决：

为应用程序设计一个面向对象的概念，如果员工不能解决问题，员工可以根据他们的资历级别发送他们的来电。

我选择了责任链模式，我也使用了Null模式。请回顾OOP原则和具体的设计模式的实现。

单元测试只是一个代码示例。

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace DesignPatternsQuestions
{
    [TestClass]
    public class ChainOfResponsibilityTest
    {
        [TestMethod]
        public void PhoneCallDispatchCORTest()
        {
            PhoneCallHandler gilad = new PhoneCallHandler(new LowLevel("Gilad"));
            PhoneCallHandler bonno = new PhoneCallHandler(new LowLevel("Bonno"));
            PhoneCallHandler batel = new PhoneCallHandler(new MediumLevel("Batel"));
            PhoneCallHandler daniel = new PhoneCallHandler(new HighLevel("Daniel"));
            gilad.RegisterNext(batel);
            bonno.RegisterNext(batel);
            batel.RegisterNext(daniel);

            BankPhoneCall call1 = new BankPhoneCall(1500);
            bool res = gilad.GetPhoneCall(call1);
            Assert.IsTrue(res);
        }
    }

    public interface IPhoneCall
    {
        int Budget { get; set; }
    }

    public class BankPhoneCall :IPhoneCall
    {

        public BankPhoneCall(int budget)
        {
            Budget = budget;
        }

        public int Budget { get; set; }
    }

    public interface IPhoneCallHandler
    {
        bool GetPhoneCall(IPhoneCall phoneCall);
        //the same item is able to call next Item in the chain of command
        void RegisterNext(IPhoneCallHandler employee);
    }

    public class PhoneCallHandler : IPhoneCallHandler
    {
        private IPhoneCallHandler _nextCallHandler = EndOfChainHandler.Instance;
        private Employee _employee;

        public PhoneCallHandler(Employee employee)
        {
            _employee = employee;
        }
        public bool GetPhoneCall(IPhoneCall phoneCall)
        {
            bool res = _employee.Resolve(phoneCall);
            if (!res)
            {
                //handle _nextcallHandler == null with null pattern
                return _nextCallHandler.GetPhoneCall(phoneCall);
            }
            return res;
        }

        public void RegisterNext(IPhoneCallHandler nextCallHandler)
        {
            _nextCallHandler = nextCallHandler;
        }
    }


    /// <summary>
    /// null pattern
    /// </summary>
    public sealed class EndOfChainHandler : IPhoneCallHandler
    {
        private static readonly Lazy<EndOfChainHandler> lazy = new Lazy<EndOfChainHandler>(()=> new EndOfChainHandler());
        public static EndOfChainHandler Instance { get { return lazy.Value; } }
        public bool GetPhoneCall(IPhoneCall phoneCall)
        {
            return false;
        }

        public void RegisterNext(IPhoneCallHandler employee)
        {
            throw  new InvalidOperationException("can't register next to null");
        }
    }

    public abstract class Employee
    {
        protected int _maxBudget;

        public string Name { get;set; }
        public Employee(string name, int maxBudget)
        {
            _maxBudget = maxBudget;
            Name = name;
        }

        public bool Resolve(IPhoneCall phoneCall)
        {
            return phoneCall.Budget <= _maxBudget;
        }
    }
    public class LowLevel : Employee
    {
        public LowLevel(string name)
            : base(name, 1000)
        {
        }
    }

    public class MediumLevel : Employee
    {
        public MediumLevel(string name)
            : base(name, 5000)
        {
        }
    }

    public class HighLevel : Employee
    {
        public HighLevel(string name)
            : base(name, 10000)
        {
        }
    }
}

Answer 1

评论

做得好，在这个实现中我不会做什么改变。我会授予你卑微的徽章，因为你把自己当成了LowLevel的雇员:)

延迟和空模式实现得很好(除了可能引入空->的小问题外，请参阅次要问题)。责任链看上去是在所难免的。您甚至在处理程序和员工之间使用了访问者模式。每个特定的员工都会产生不同的处理电话的行为。

次要问题

• 在我看来，IPhoneCall作为接口似乎太过分了。这只是一只波科。
• 在公共入口点(如public PhoneCallHandler(Employee employee) )中检查针对null的参数。
• GetPhoneCall可以写得更紧凑：return _employee.Resolve(phoneCall) || _nextCallHandler.GetPhoneCall(phoneCall);。
• RegisterNext不应该允许null，因为这绕过了您的EndOfChainHandler.Instance模式以避免null处理。