我在Russ Olsen 的“Ruby 中的设计模式”中阅读了 如何在 Ruby 中实现观察者模式。我注意到这种模式的 Ruby 实现比 C# 实现简单得多，例如Jesse Liberty 和 Alex Horovitz 在“Programming .NET 3.5”中展示的实现。
因此，我使用“Ruby 中的设计模式”算法重写了“Programming .NET 3.5”观察者模式示例（pdf 版的第 251 页），两种实现的源代码都可以从上述网站下载。
下面是重写的例子，告诉我你怎么看？
我们真的需要使用事件和委托来使用 C# 中的观察者模式吗？
更新
阅读评论后，我想问这个问题：
除了使代码更短之外，还有其他理由使用委托和事件吗？而且我不谈论 GUI 编程。
Update2 我终于明白了，委托只是一个函数指针，事件是委托的更安全版本，它只允许两个操作 += 和 -=。
我对“Programming .NET 3.5”示例的重写：
using System;
using System.Collections.Generic;
namespace MyObserverPattern
{
class Program
{
static void Main()
{
DateTime now = DateTime.Now;
// Create new flights with a departure time and add from and to destinations
CarrierSchedule jetBlue = new CarrierSchedule("JetBlue", now);
jetBlue.Attach(new AirTrafficControl("Boston"));
jetBlue.Attach(new AirTrafficControl("Seattle"));
// ATCs will be notified of delays in departure time
jetBlue.DepartureDateTime =
now.AddHours(1.25); // weather delay
jetBlue.DepartureDateTime =
now.AddHours(1.75); // weather got worse
jetBlue.DepartureDateTime =
now.AddHours(0.5); // security delay
jetBlue.DepartureDateTime =
now.AddHours(0.75); // Seattle puts a ground stop in place
// Wait for user
//Console.Read();
}
}
// Subject: This is the thing being watched by Air Traffic Control centers
abstract class AirlineSchedule
{
// properties
public string Name { get; set; }
public string DeparturnAirport { get; set; }
public string ArrivalAirport { get; set; }
private DateTime departureDateTime;
private List<IATC> observers = new List<IATC>();
public AirlineSchedule(string airline,
string outAirport,
string inAirport,
DateTime leaves )
{
this.Name = airline;
this.DeparturnAirport = outAirport;
this.ArrivalAirport = inAirport;
this.DepartureDateTime = leaves;
}
// Here is where we actually attach our observers (ATCs)
public void Attach(IATC atc)
{
observers.Add(atc);
}
public void Detach(IATC atc)
{
observers.Remove(atc);
}
public void OnChange(AirlineSchedule asched)
{
if (observers.Count != 0)
{
foreach (IATC o in observers)
o.Update(asched);
}
}
public DateTime DepartureDateTime
{
get { return departureDateTime; }
set
{
departureDateTime = value;
OnChange(this);
Console.WriteLine("");
}
}
}// class AirlineSchedule
// A Concrete Subject
class CarrierSchedule : AirlineSchedule
{
// Jesse and Alex only really ever need to fly to one place...
public CarrierSchedule(string name, DateTime departing) :
base(name, "Boston", "Seattle", departing)
{
}
}
// An Observer
interface IATC
{
void Update(AirlineSchedule sender);
}
// The Concrete Observer
class AirTrafficControl : IATC
{
public string Name { get; set; }
public AirTrafficControl(string name)
{
this.Name = name;
}
public void Update(AirlineSchedule sender)
{
Console.WriteLine(
"{0} Air Traffic Control Notified:\n {1}'s flight 497 from {2} " +
"to {3} new deprture time: {4:hh:mmtt}",
Name,
sender.Name,
sender.DeparturnAirport,
sender.ArrivalAirport,
sender.DepartureDateTime );
Console.WriteLine("---------");
}
}
}
这里提到了Ruby代码：
module Subject
def initialize
@observers=[]
end
def add_observer(observer)
@observers << observer
end
def delete_observer(observer)
@observers.delete(observer)
end
def notify_observers
@observers.each do |observer|
observer.update(self)
end
end
end
class Employee
include Subject
attr_reader :name, :address
attr_reader :salary
def initialize( name, title, salary)
super()
@name = name
@title = title
@salary = salary
end
def salary=(new_salary)
@salary = new_salary
notify_observers
end
end
class TaxMan
def update( changed_employee )
puts("Send #{changed_employee.name} a new tax bill!")
end
end
fred = Employee.new('Fred', 'Crane Operator', 30000.0)
tax_man = TaxMan.new
fred.add_observer(tax_man)
这是我重写的“Programming .NET 3.5”示例：
using System;
namespace Observer
{
class Program
{
static void Main()
{
DateTime now = DateTime.Now;
// Create new flights with a departure time and add from and to destinations
CarrierSchedule jetBlue = new CarrierSchedule("JetBlue", now);
jetBlue.Attach(new AirTrafficControl("Boston"));
jetBlue.Attach(new AirTrafficControl("Seattle"));
// ATCs will be notified of delays in departure time
jetBlue.DepartureDateTime =
now.AddHours(1.25); // weather delay
jetBlue.DepartureDateTime =
now.AddHours(1.75); // weather got worse
jetBlue.DepartureDateTime =
now.AddHours(0.5); // security delay
jetBlue.DepartureDateTime =
now.AddHours(0.75); // Seattle puts a ground stop in place
// Wait for user
Console.Read();
}
}
// Generic delegate type for hooking up flight schedule requests
public delegate void ChangeEventHandler<T,U>
(T sender, U eventArgs);
// Customize event arguments to fit the activity
public class ChangeEventArgs : EventArgs
{
public ChangeEventArgs(string name, string outAirport, string inAirport, DateTime leaves)
{
this.Airline = name;
this.DeparturnAirport = outAirport;
this.ArrivalAirport = inAirport;
this.DepartureDateTime = leaves;
}
// Our Properties
public string Airline { get; set; }
public string DeparturnAirport { get; set; }
public string ArrivalAirport { get; set; }
public DateTime DepartureDateTime { get; set; }
}
// Subject: This is the thing being watched by Air Traffic Control centers
abstract class AirlineSchedule
{
// properties
public string Name { get; set; }
public string DeparturnAirport { get; set; }
public string ArrivalAirport { get; set; }
private DateTime departureDateTime;
public AirlineSchedule(string airline, string outAirport, string inAirport, DateTime leaves)
{
this.Name = airline;
this.DeparturnAirport = outAirport;
this.ArrivalAirport = inAirport;
this.DepartureDateTime = leaves;
}
// Event
public event ChangeEventHandler<AirlineSchedule, ChangeEventArgs> Change;
// Invoke the Change event
public virtual void OnChange(ChangeEventArgs e)
{
if (Change != null)
{
Change(this, e);
}
}
// Here is where we actually attach our observers (ATCs)
public void Attach(AirTrafficControl airTrafficControl)
{
Change +=
new ChangeEventHandler<AirlineSchedule, ChangeEventArgs>
(airTrafficControl.Update);
}
public void Detach(AirTrafficControl airTrafficControl)
{
Change -= new ChangeEventHandler<AirlineSchedule, ChangeEventArgs>
(airTrafficControl.Update);
}
public DateTime DepartureDateTime
{
get { return departureDateTime; }
set
{
departureDateTime = value;
OnChange(new ChangeEventArgs(
this.Name,
this.DeparturnAirport,
this.ArrivalAirport,
this.departureDateTime));
Console.WriteLine("");
}
}
}
// A Concrete Subject
class CarrierSchedule : AirlineSchedule
{
// Jesse and Alex only really ever need to fly to one place...
public CarrierSchedule(string name, DateTime departing):
base(name,"Boston", "Seattle", departing)
{
}
}
// An Observer
interface IATC
{
void Update(AirlineSchedule sender, ChangeEventArgs e);
}
// The Concrete Observer
class AirTrafficControl : IATC
{
public string Name { get; set; }
// Constructor
public AirTrafficControl(string name)
{
this.Name = name;
}
public void Update(AirlineSchedule sender, ChangeEventArgs e)
{
Console.WriteLine(
"{0} Air Traffic Control Notified:\n {1}'s flight 497 from {2} " +
"to {3} new deprture time: {4:hh:mmtt}",
Name,
e.Airline,
e.DeparturnAirport,
e.ArrivalAirport,
e.DepartureDateTime);
Console.WriteLine("---------");
}
public CarrierSchedule CarrierSchedule { get; set; }
}
}