设计模式-观察者模式

定义了一种一对多的依赖关系，当一个对象的状态发生改变时，其所有依赖者都会收到通知并自动更新。

示例

//抽象通知者
abstract class Subject
{
    private IList<Observer> observers = new List<Observer>();
    //增加观察者
    public void Attach(Observer observer)
    {
        observers.Add(observer);
    }
    //移除观察者
    public void Detach(Observer observer)
    {
        observers.Remove(observer);
    }
    //通知
    public void Notify()
    {
        observers.Foreach(o => o.Update())
    }
}
//抽象观察者
interface class IObserver
{
    void Update();
}
//具体通知者
class ConcreateSubject : Subject
{
    private string subjectState;
    //具体被观察者的状态
    public string SubjectState
    {
        get{return subjectState;}
        set{subjectState = value}
    }
}
//具体观察者
class ConcreatObserver : IObserver
{
    private string name;
    private string observerState;
    private ConcreateSubject subject;
    public ConcreatObserver(ConcreateSubject subject, string name)
    {
        this.subject = subject;
        this.name = name;
    }
    public void Update()
    {
        observerState = subject.SubjectState;
        Console.WriteLine("观察者{0}的新状态是{1}", name, observerState);
    }
    public ConcreateSubject Subject
    {
        get{return subject;}
        set{subject = value;}
    }
}
//Client
ConcreateSubject subject = new ConcreateSubject();l
subject.Attach(new ConcreatObserver(subject, "X"));
subject.Attach(new ConcreatObserver(subject, "Y"));
subject.Attach(new ConcreatObserver(subject, "Z"));
subject.SubjectState = "ABC";
subject.Notify();

//使用事件
//通知者接口
interface Subject
{
    void Noticy();
    string SubjectState
    {
        get;
        set;
    }
}
//具体通知者
class ConcreateSubject : Subject
{
    public event EventHandler Update;
    private string action;
    public void Notify()
    {
        Update();
    }
    public string SubjectState
    {
        get{return action;}
        set{action = value;}
    }
}
//具体观察者
class ConcreatObserver1
{
    private string name;
    private Subject subject;
    public ConcreatObserver1(Subject subject, string name)
    {
        this.subject = subject;
        this.name = name;
    }
    public void Update1()
    {
        observerState = subject.SubjectState;
        Console.WriteLine("观察者{0}的新状态是{1}", name, observerState);
    }
}
class ConcreatObserver2
{
    private string name;
    private Subject subject;
    public ConcreatObserver2(Subject subject, string name)
    {
        this.subject = subject;
        this.name = name;
    }
    public void Update2()
    {
        observerState = subject.SubjectState;
        Console.WriteLine("观察者{0}的新状态是{1}", name, observerState);
    }
}
//Client
ConcreateSubject subject = new ConcreateSubject();
subject.Update += new EventHandler(new ConcreatObserver1(subject, "X").Update1());
subject.Update += new EventHandler(new ConcreatObserver2(subject, "Y").Update2());
subject.SubjectState = "ABC";
subject.Notify();