Apply stock quote changes using observer pattern

Question

I am implementing observer pattern(refering codeproject) for stock quote update. I have created an interface for Subject and Observer. I have created instances for Subject and Observer and also the functionality to register, notify and update. Kindly let me know the approach is correct

public interface IObserver
 {
 void update(double value);
 }
}

//subject

public interface ISubject
 {
 void Register(IObserver o);
 void UnRegister(IObserver o);
 void notify();
 }

//Observer instance

public class InfosysStock : IObserver
 {
 private ISubject _subject;
 private double _latestvalue = 0;
 public InfosysStock(ISubject subject)
 {
 _subject = subject;
 _subject.Register(this);
 }
 public void update(double value)
 {
 _latestvalue = value;
 display();
 }
 private void display()
 {
 Console.WriteLine("The latest value is : " + _latestvalue);
 }
 public void unsubscribe()
 {
 _subject.UnRegister(this);
 }
 }

//Subject Instance

public class StockMarket : ISubject
 {
 List<IObserver> observers = new List<IObserver>();
 public int _stockvalue = 0;
 public void setValue(int v)
 {
 _stockvalue = v;
 notify();
 }
 public void notify()
 {
 foreach (var observer in observers)
 {
 observer.update(_stockvalue);
 }
 }
 public void Register(IObserver o)
 {
 observers.Add(o);
 }
 public void UnRegister(IObserver o)
 {
 int idx = observers.IndexOf(o);
 observers.RemoveAt(idx);
 }
 }

Finally the main class

StockMarket stockmarket = new StockMarket();
InfosysStock infy = new InfosysStock(stockmarket);
stockmarket.setValue(15);
stockmarket.setValue(21);
 infy.unsubscribe();
 Console.ReadLine();

• t3chb0t: This is not how it is supposed to be used. setValue should automatiacally notify listeners. Having to call notify manually is pointless and makes the whole pattern unnecessary.
• krishna_v: @t3chb0t I have modified the code. Does it look fine now? any other modifications to be made?
• CharlesNRice: Is this just to learn? why not use the built in interfaces and reactive extensions?
• krishna_v: I am implementing it newly and would like to get the feedback if the approach is right?

Answer 1

1. If you are implementing this pattern for learning, then it is OK.

Otherwise, you can use built-in Observer Pattern of C#.

2. Think about readable:

 public void UnRegister(IObserver o)
 {
 int idx = observers.IndexOf(o);
 observers.RemoveAt(idx);
 }
 }

There are some redundant empty lines in your code. Inaddition, "o" is not a good variable name. I think you can change it to "observer".

3.You don't need to retrieve index of an object and then you remove it via the index. It will reduce the performance:

 public void UnRegister(IObserver o)
 {
 int idx = observers.IndexOf(o);
 observers.RemoveAt(idx);
 }

You can use Remove() method to remove an object from the list directly:

 public void UnRegister(IObserver o)
 {
 observers.Remove(o);
 }