设计模式 - 11）观察者模式

/// <summary>
/// 抽象观察者接口
/// </summary>
interface Observer
{         
    void Update();
}

/// <summary>
/// 具体观察者
/// </summary>
class ConcreteObserver : Observer
{
    string _name;
    string _observerState;
    ConcreteSubject _subject;
    public ConcreteSubject Subject
    {
        get { return _subject; }
        set { _subject = value; }
    }
    public ConcreteObserver(ConcreteSubject sub, string name)
    {
        this._subject = sub;
        this._name = name;
    }

    public void Update()
    {
        _observerState = Subject.SubjectState;
        Console.WriteLine(string.Format("通知{0}:{1}, no stock", _name, _observerState));
    }
}
 

/// <summary>
/// 抽象发布类
/// </summary>
abstract class Subject
{
    private IList<Observer> observers = new List<Observer>();
    public void Attach(Observer ob)
    {
        observers.Add(ob);
    }

    public void Detach(Observer ob)
    {
        observers.Remove(ob);
    }

    public void Notify()
    {
        foreach (Observer ob in observers)
        {
            ob.Update();
        }
    }                
}

/// <summary>
/// 具体发布类
/// </summary>
class ConcreteSubject : Subject
{
    string subjectState;
    public string SubjectState
    {
        get { return subjectState; }
        set { subjectState = value; }
    }
}


// 业务代码
ConcreteSubject sub = new ConcreteSubject();
sub.Attach(new ConcreteObserver(sub, "x"));
sub.Attach(new ConcreteObserver(sub, "y"));

sub.SubjectState = "ABC";
sub.Notify();   

但是并不是每个观察者都会有 Update 这个方法，因此：

/// <summary>
/// 具体观察者
/// </summary>
class ConcreteObserver
{
    string _name;
    Subject _sub;
    public ConcreteObserver(string name, Subject sub)
    {
        this._name = name;
        this._sub = sub;
    }

    public void Closing()
    {
        Console.WriteLine(string.Format("通知{0}:{1} : Close, no stock", _name, _sub.SubjectState));
    }

    public void Open()
    {
        Console.WriteLine(string.Format("通知{0}:{1} : Open, no stock", _name, _sub.SubjectState));
    }
}
    
/// <summary>
/// 抽象发布类
/// </summary>
interface Subject
{
    void Notify();
    string SubjectState
    {
        get;
        set;
    }
}

delegate void EventHandler();

class Boss : Subject
{
    string action;
    public string SubjectState
    {
        get { return action; }
        set { action = value; }
    }               
        
    public event EventHandler Update;

    public void Notify()
    {
        Update();
    }
}

        
// 业务代码        
Boss hu = new Boss();

ConcreteObserver ob1 = new ConcreteObserver("boyA", hu);
ConcreteObserver ob2 = new ConcreteObserver("boyB", hu);

hu.Update += new EventHandler(ob1.Closing);
hu.Update += new EventHandler(ob2.Open);

hu.SubjectState = "I am Coming";

hu.Notify();