观察者模式(observer)

class Program
{
//观察者模式 [əb'zə:və, ɔb-]
static void Main(string[] args)
{
ConcreteSubject s = new ConcreteSubject();
s.Attach(new ConcreteObserver(s, "a"));
s.Attach(new ConcreteObserver(s, "b"));
s.Attach(new ConcreteObserver(s, "c"));

s.SubjectState = "run";
s.Notify();
Console.Read();
}
//抽象观察者
abstract class Observer
{
public abstract void Update();
}

//抽象通知者
abstract class Subject
{
IList<Observer> listObserver = new List<Observer>();

public void Attach(Observer observer)
{
listObserver.Add(observer);
}

public void Detach(Observer observer)
{
listObserver.Remove(observer);
}

public void Notify()
{
foreach (Observer o in listObserver)
{
o.Update();
}
}
}
//具体通知者
class ConcreteSubject : Subject
{
public string SubjectState { get; set; }
}

//具体观察者
class ConcreteObserver : Observer
{
private string name;
private string observerState;
private ConcreteSubject subject;
public ConcreteSubject Subject
{
get{return subject;}
set{subject=value;}
}
public ConcreteObserver(ConcreteSubject subject, string name)
{
this.subject = subject;
this.name = name;
}

public override void Update()
{
observerState = subject.SubjectState;
Console.Write("observer {0} is state {1} \n ", name, observerState);
}

}
}