Observer

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace Observer{ class Program { /// <summary> /// Entry point into console application. /// </summary> static void Main() { #region subject // Configure Observer pattern ConcreteSubject s = new ConcreteSubject(); s.Attach(new ConcreteObserver(s, "X")); s.Attach(new ConcreteObserver(s, "Y")); s.Attach(new ConcreteObserver(s, "Z")); // Change subject and notify observers s.SubjectState = "ABC"; s.Notify(); // Wait for user Console.ReadKey(); #endregion #region stock // Create IBM stock and attach investors IBM ibm = new IBM("IBM", 120.00); ibm.Attach(new Investor("Sorros")); ibm.Attach(new Investor("Berkshire")); // Fluctuating prices will notify investors ibm.Price = 120.10; ibm.Price = 121.00; ibm.Price = 120.50; ibm.Price = 120.75; // Wait for user Console.ReadKey(); #endregion } } #region Subject /// <summary> /// The 'Subject' abstract class /// </summary> abstract class Subject { private List<Observer> _observers = new List<Observer>(); public void Attach(Observer observer) { _observers.Add(observer); } public void Detach(Observer observer) { _observers.Remove(observer); } public void Notify() { foreach (Observer o in _observers) { o.Update(); } } } /// <summary> /// The 'ConcreteSubject' class /// </summary> class ConcreteSubject : Subject { private string _subjectState; // Gets or sets subject state public string SubjectState { get { return _subjectState; } set { _subjectState = value; } } } /// <summary> /// The 'Observer' abstract class /// </summary> abstract class Observer { public abstract void Update(); } /// <summary> /// The 'ConcreteObserver' class /// </summary> class ConcreteObserver : Observer { private string _name; private string _observerState; private ConcreteSubject _subject; // Constructor public ConcreteObserver(ConcreteSubject subject, string name) { this._subject = subject; this._name = name; } public override void Update() { _observerState = _subject.SubjectState; Console.WriteLine("Observer {0}'s new state is {1}", _name, _observerState); } // Gets or sets subject public ConcreteSubject Subject { get { return _subject; } set { _subject = value; } } } #endregion #region Stock /// <summary> /// The 'Subject' abstract class /// </summary> abstract class Stock { private string _symbol; private double _price; private List<IInvestor> _investors = new List<IInvestor>(); // Constructor public Stock(string symbol, double price) { this._symbol = symbol; this._price = price; } public void Attach(IInvestor investor) { _investors.Add(investor); } public void Detach(IInvestor investor) { _investors.Remove(investor); } public void Notify() { foreach (IInvestor investor in _investors) { investor.Update(this); } Console.WriteLine(""); } // Gets or sets the price public double Price { get { return _price; } set { if (_price != value) { _price = value; Notify(); } } } // Gets the symbol public string Symbol { get { return _symbol; } } } /// <summary> /// The 'ConcreteSubject' class /// </summary> class IBM : Stock { // Constructor public IBM(string symbol, double price) : base(symbol, price) { } } /// <summary> /// The 'Observer' interface /// </summary> interface IInvestor { void Update(Stock stock); } /// <summary> /// The 'ConcreteObserver' class /// </summary> class Investor : IInvestor { private string _name; private Stock _stock; // Constructor public Investor(string name) { this._name = name; } public void Update(Stock stock) { Console.WriteLine("Notified {0} of {1}'s " + "change to {2:C}", _name, stock.Symbol, stock.Price); } // Gets or sets the stock public Stock Stock { get { return _stock; } set { _stock = value; } } } #endregion}