C# 与委托(delegate)的责任链

Question

为了我的理解目的，我已经实现了责任链模式。

//Abstract Base Type

public abstract class CustomerServiceDesk
{
 protected CustomerServiceDesk _nextHandler;
 public abstract  void ServeCustomers(Customer _customer);
 public void SetupHadler(CustomerServiceDesk _nextHandler)
 {
          this._nextHandler = _nextHandler;
 }
}

 public class FrontLineServiceDesk:CustomerServiceDesk
 {
     public override void ServeCustomers(Customer _customer)
     {
        if (_customer.ComplaintType == ComplaintType.General)
         {
           Console.WriteLine(_customer.Name + " Complaints are registered  ; 
           will be served soon by FrontLine Help Desk..");
         }

        else 
        {
          Console.WriteLine(_customer.Name + " 
          is redirected to Critical Help Desk");

          _nextHandler.ServeCustomers(_customer);
        }

        }
  }
public class CriticalIssueServiceDesk:CustomerServiceDesk
{
    public override void ServeCustomers(Customer _customer)
    {
        if (_customer.ComplaintType == ComplaintType.Critical)
        {
            Console.WriteLine(_customer.Name + 
            "Complaints are registered  ; will be served soon 
             by Critical Help Desk");
        }
        else if (_customer.ComplaintType == ComplaintType.Legal)
        {
            Console.WriteLine(_customer.Name +
            "is redirected to Legal Help Desk");
            _nextHandler.ServeCustomers(_customer);
        }
    }
}

public class LegalissueServiceDesk :CustomerServiceDesk
{
    public override void ServeCustomers(Customer _customer)
    {
        if (_customer.ComplaintType == ComplaintType.Legal)
        {
            Console.WriteLine(_customer.Name + 
            "Complaints are registered  ; 
             will be served soon by legal help desk");
        }
    }
}


public class Customer
{
    public string Name { get; set; }
    public ComplaintType ComplaintType { get; set; }
}


public enum ComplaintType
{
    General,
    Critical,
    Legal
}

void Main()
{
CustomerServiceDesk _frontLineDesk = new FrontLineServiceDesk();
CustomerServiceDesk _criticalSupportDesk = new CriticalIssueServiceDesk();
CustomerServiceDesk _legalSupportDesk = new LegalissueServiceDesk();
_frontLineDesk.SetupHadler(_criticalSupportDesk);
_criticalSupportDesk.SetupHadler(_legalSupportDesk);

Customer _customer1 = new Customer();
_customer1.Name = "Microsoft";
_customer1.ComplaintType = ComplaintType.General;

Customer _customer2 = new Customer();
_customer2.Name = "SunSystems";
_customer2.ComplaintType = ComplaintType.Critical;

Customer _customer3 = new Customer();
_customer3.Name = "HP";
_customer3.ComplaintType = ComplaintType.Legal;

_frontLineDesk.ServeCustomers(_customer1);
_frontLineDesk.ServeCustomers(_customer2);
_frontLineDesk.ServeCustomers(_customer3);
}

问题

在不破坏责任链的情况下，我如何应用委托(delegate)和事件来重写代码？

Answer 1

如果我理解正确...您可以做的是删除 SetupHandler 方法并引入 OnElevateQuery 事件是您的 CriticalHelpDesk 对象可以处理 FrontLineHelpDesk.OnElevateQuery 事件，您的 LegalHelpDesk 对象可以处理 CriticalHelpDesk.OnElevateQuery 事件。 OnElevateQuery 事件可以在事件参数中传递客户。

例子

public abstract class CustomerServiceDesk
{
    public delegate void ElevateQueryEventHandler(Customer c);
    public event ElevateQueryEventHandler OnElevateQuery;
    public abstract void ServeCustomer(Customer c);
}

public class FrontLineServiceDesk : CustomerServiceDesk
{
    public override void ServeCustomer(Customer c)
    {
        switch (c.ComplaintType)
        {
            case ComplaintType.General:
                Console.WriteLine(c.Name + " Complaints are registered; will be served soon by FrontLine Help Desk");
                break;
            default:
                OnElevateQuery(c);
        }
    }
}

public class CriticalIssueServiceDesk : CustomerServiceDesk
{
    public override void ServeCustomer(Customer c)
    {
        switch (c.ComplaintType)
        {
            case ComplaintType.Critical:
                Console.WriteLine(c.Name + " Complaints are registered; will be served soon by Critical Help Desk");
                break;
            case ComplaintType.Legal:
                OnElevateQuery(c);
                break;
            default:
                Console.WriteLine("Unable to find appropriate help desk for your complaint.");
                break;
        }
    }
}

public class LegalIssueServiceDesk : CustomerServiceDesk
{
    public override void ServeCustomer(Customer c)
    {
        if (c.CompliantType == CompliantType.Legal)
        {
            Console.WriteLine(c.Name + " Complaints are registered; will be served soon by Legal Help Desk");
        }
        else
        {
            // you could even hook up the FrontLine.ServeCustomer event 
            // to the OnElevateQuery event of this one so it takes the 
            // query back to the start of the chain (if it accidently ended up here).
            Console.WriteLine("Wrong department");
        }
    }
}

用法

CustomerServiceDesk _frontLine = new FrontLineServiceDesk();
CustomerServiceDesk _criticalLine = new CriticalLineServiceDesk();
CustomerServiceDesk _legalLine = new LegalLineServiceDesk();
// hook up events
_frontLine.OnElevateQuery += _critialLine.ServeCustomer;
_criticalLine.OnElevateQuery += _legalLine.ServeCustomer;

Customer _customer1 = new Customer(); 
_customer1.Name = "Microsoft"; 
_customer1.ComplaintType = ComplaintType.General; 

Customer _customer2 = new Customer(); 
_customer2.Name = "SunSystems"; 
_customer2.ComplaintType = ComplaintType.Critical; 

Customer _customer3 = new Customer(); 
_customer3.Name = "HP"; 
_customer3.ComplaintType = ComplaintType.Legal;

_frontLine.ServeCustomer(_customer1);
_frontLine.ServeCustomer(_customer2);
_frontLine.ServeCustomer(_customer3);

但是，由于查询类型基于枚举 ComplaintType，您是否考虑过使用可能返回通用接口(interface)的 HelpDeskFactory，例如IHelpDesk。听起来您也可以针对此特定示例使用 Strategy Pattern。