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Add stock example on Observer pattern

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This commit is contained in:
Petrutiu Mihai
2016-06-28 17:26:33 +03:00
parent 4a69b3da17
commit 5d639bf0ab
13 changed files with 262 additions and 34 deletions
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61
src/ObserverPattern/ObserverPatternExamples.cs
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@@ -1,4 +1,5 @@
using ObserverPattern.Twits;
using ObserverPattern.StockUpdateEvents;
using ObserverPattern.Twits;
using System;
using System.Collections.Generic;
using System.Linq;
@@ -11,8 +12,66 @@ namespace ObserverPattern
{
public static void Run()
{
Console.WriteLine(GetDescription());
Console.WriteLine(GetActors());
Console.WriteLine(IsThisPubSub());
StockUpdateEventsExample stockExample = new StockUpdateEventsExample();
stockExample.RunSimple();
GoToNextStep();
Console.WriteLine("Same business logic using RX");
stockExample.RunReactive();
Console.WriteLine(GetLapsedLinstenerProblem());
ObservableTwitsExample obsTwits = new ObservableTwitsExample();
obsTwits.Run();
GoToNextStep();
}
private static string GetDescription()
{
return @"
The observer pattern is a software design pattern in which an object, called the subject,
maintains a list of its dependents, called observers, and notifies them automatically of any state changes,
usually by calling one of their methods. ";
}
private static string IsThisPubSub()
{
return @"
Observer/Observable pattern is mostly implemented in a synchronous way,
i.e. the observable calls the appropriate method of all its observers when some event occurs.
The Publisher/Subscriber pattern is mostly implemented in an asynchronous way (using message queue).
In the Observer/Observable pattern, the observers are aware of the observable.
Whereas, in Publisher/Subscriber, publishers and subscribers don't need to know each other.
They simply communicate with the help of message queues.
";
}
private static string GetActors()
{
return @"
Subject -> Notifies interested observers when an event occurs
Observer -> Registers to a subject, to be notified when a specific event happens
";
}
private static string GetLapsedLinstenerProblem()
{
return @"
The leak happens when a listener fails to unsubscribe from the publisher when it no longer needs to listen.
Consequently, the publisher still holds a reference to the observer which prevents it from being garbage collected
— including all other objects it is referring to — for as long as the publisher is alive, which could be until the end of the application.
This causes not only a memory leak, but also a performance degradation with an 'uninterested' observer receiving and acting on unwanted events";
}
private static void GoToNextStep()
{
Console.ReadKey();
Console.Clear();
}
}
}

29
src/ObserverPattern/StockUpdateEvents/AaplObserver.cs Normal file
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@@ -0,0 +1,29 @@
using System;
namespace ObserverPattern.StockUpdateEvents
{
/// <summary>
/// Observer
/// </summary>
public class AaplObserver
{
double? oldValue;
public AaplObserver(StockSubject stockObservable)
{
stockObservable.StockUpdated += (obj, e) => PrintNewValue(e.Stock);
}
private void PrintNewValue(Stock stock)
{
if (stock.Name == "AAPL")
{
if (oldValue.HasValue)
Console.WriteLine("Apple price updated from {0} to {1}", oldValue, stock.Value);
else
Console.WriteLine("Apple has a new price, new value is: {0}", stock.Value);
oldValue = stock.Value;
}
}
}
}

25
src/ObserverPattern/StockUpdateEvents/LondonStockObserver.cs Normal file
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@@ -0,0 +1,25 @@
using System;
namespace ObserverPattern.StockUpdateEvents
{
public class LondonStockObserver
{
double? oldValue;
public LondonStockObserver(StockSubject stockObservable)
{
stockObservable.StockUpdated += (obj, e) => PrintStockValue(e.Stock);
}
private void PrintStockValue(Stock stock)
{
if (stock.Name == "FTSE")
{
if (oldValue.HasValue)
Console.WriteLine("The Financial Times Stock Exchange 100 Index price updated from {0} to {1}", oldValue, stock.Value);
else
Console.WriteLine("The Financial Times Stock Exchange 100 Index has a new price, new value is: {0}", stock.Value);
oldValue = stock.Value;
}
}
}
}

10
src/ObserverPattern/StockUpdateEvents/Stock.cs Normal file
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@@ -0,0 +1,10 @@
namespace ObserverPattern.StockUpdateEvents
{
public class Stock
{
public string Name { get; set; }
public int Quantity { get; set; }
public double Value { get; set; }
}
}

18
src/ObserverPattern/StockUpdateEvents/StockSubject.cs Normal file
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@@ -0,0 +1,18 @@
using System;
namespace ObserverPattern.StockUpdateEvents
{
/// <summary>
/// Subject
/// </summary>
public class StockSubject
{
public void UpdateStockValue(Stock s)
{
StockUpdated?.Invoke(this, new StockUpdateEventArgs(s));
}
public event EventHandler<StockUpdateEventArgs> StockUpdated;
}
}

12
src/ObserverPattern/StockUpdateEvents/StockUpdateEventArgs.cs Normal file
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@@ -0,0 +1,12 @@
namespace ObserverPattern.StockUpdateEvents
{
public class StockUpdateEventArgs
{
public Stock Stock { get; set; }
public StockUpdateEventArgs(Stock stock)
{
Stock = stock;
}
}
}

65
src/ObserverPattern/StockUpdateEvents/StockUpdateEventsExample.cs Normal file
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@@ -0,0 +1,65 @@
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive;
using System.Reactive.Linq;
using System.Threading.Tasks;
namespace ObserverPattern.StockUpdateEvents
{
public class StockUpdateEventsExample
{
public void RunSimple()
{
StockSubject stockSubject = new StockSubject();
LondonStockObserver londonObserver = new LondonStockObserver(stockSubject);
AaplObserver aaplObserver = new AaplObserver(stockSubject);
PublishUpdateStocks(stockSubject);
}
public void RunReactive()
{
StockSubject stockSubject = new StockSubject();
var londonObserver = Observable.FromEventPattern<StockUpdateEventArgs>(
ev => stockSubject.StockUpdated += ev,
ev => stockSubject.StockUpdated -= ev).Where(s => s.EventArgs.Stock.Name == "FTSE");
var aaplObserver = Observable.FromEventPattern<StockUpdateEventArgs>(
ev => stockSubject.StockUpdated += ev,
ev => stockSubject.StockUpdated -= ev).Where(s => s.EventArgs.Stock.Name == "AAPL");
using (londonObserver.Subscribe(PrintLondonStockPriceUpdate))
using (aaplObserver.Subscribe(PrintAaplStockPriceUpdate))
{
PublishUpdateStocks(stockSubject);
}
}
private void PrintAaplStockPriceUpdate(EventPattern<StockUpdateEventArgs> eventP)
{
Console.WriteLine("apple updated, new value: {0}", eventP.EventArgs.Stock.Value);
}
private void PrintLondonStockPriceUpdate(EventPattern<StockUpdateEventArgs> eventP)
{
Console.WriteLine("london stock updated, new value: {0}", eventP.EventArgs.Stock.Value);
}
private static void PublishUpdateStocks(StockSubject stockSubject)
{
stockSubject.UpdateStockValue(new Stock { Name = "AAPL", Value = 3 });
stockSubject.UpdateStockValue(new Stock { Name = "AAPL", Value = 4 });
stockSubject.UpdateStockValue(new Stock { Name = "AAPL", Value = 5 });
stockSubject.UpdateStockValue(new Stock { Name = "AAPL", Value = 6 });
stockSubject.UpdateStockValue(new Stock { Name = "FTSE", Value = 6 });
stockSubject.UpdateStockValue(new Stock { Name = "FTSE", Value = 12 });
stockSubject.UpdateStockValue(new Stock { Name = "FTSE", Value = 2 });
stockSubject.UpdateStockValue(new Stock { Name = "FTSE", Value = 3 });
}
}
}

16
src/ObserverPattern/Twits/ObservableTwitsExample.cs
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@@ -11,16 +11,16 @@ namespace ObserverPattern.Twits
{
TwitObservable observable = new TwitObservable();
TwitUser t100 = new TwitUser("t100", observable);
TwitUser r2d2 = new TwitUser("R2-D2", observable);
using (TwitUser t100 = new TwitUser("t100", observable))
using (TwitUser r2d2 = new TwitUser("R2-D2", observable))
{
t100.Twit("El chupacapra - BOOM BOOM");
t100.Twit("El chupacapra - BOOM BOOM");
r2d2.Twit("Vamos vamos mi amor");
r2d2.Twit("Vamos vamos mi amor");
t100.Dispose();
observable.ItsGoingHomeTime();
observable.ItsGoingHomeTime();
}
}
}
}

19
src/ObserverPattern/Twits/TwitObservable.cs
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@@ -20,7 +20,7 @@ namespace ObserverPattern.Twits
if (!observers.Contains(observer))
observers.Add(observer);
return new Unsubscriber(observers, observer);
return new Unsubscriber<Twit>(observers, observer);
}
public void AddTwit(Twit twit)
@@ -37,23 +37,6 @@ namespace ObserverPattern.Twits
{
observer.OnCompleted();
}
}
private class Unsubscriber : IDisposable
{
private List<IObserver<Twit>> _observers;
private IObserver<Twit> _observer;
public Unsubscriber(List<IObserver<Twit>> observers, IObserver<Twit> observer)
{
_observers = observers;
_observer = observer;
}
public void Dispose()
{
if (!(_observer == null)) _observers.Remove(_observer);
}
}
}

24
src/ObserverPattern/Unsubscriber.cs Normal file
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@@ -0,0 +1,24 @@
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace ObserverPattern
{
public class Unsubscriber<T> : IDisposable
{
private List<IObserver<T>> _observers;
private IObserver<T> _observer;
public Unsubscriber(List<IObserver<T>> observers, IObserver<T> observer)
{
_observers = observers;
_observer = observer;
}
public void Dispose()
{
if (!(_observer == null)) _observers.Remove(_observer);
}
}
}

3
src/ObserverPattern/project.json
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@@ -2,7 +2,8 @@
"version": "1.0.0-*",
"dependencies": {
"NETStandard.Library": "1.6.0"
"NETStandard.Library": "1.6.0",
"System.Reactive": "3.0.0"
},
"frameworks": {