C# Observer Design Pattern with The IObserver<T> and IObservable<T> interfaces
C# 2022. 1. 8. 13:37 |반응형
IObserver<T> interface와 IObservable<T> interface를 이용해 Observer Design Pattern을 구현해 보자.
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Observer
{
class Program
{
static void Main(string[] args)
{
LocationTracker provider = new LocationTracker();
// Provider 생성
LocationReporter reporter1 = new LocationReporter("FixedGPS");
reporter1.Subscribe(provider);
// Observer(FixedGPS) 생성 및 Provider에 등록
LocationReporter reporter2 = new LocationReporter("MobileGPS");
reporter2.Subscribe(provider);
// Observer(MobileGPS) 생성 및 Provider에 등록
provider.TrackLocation(new Location(47.6456, -122.1312));
// FixedGPS: The current location is 47.6456, -122.1312
// MobileGPS: The current location is 47.6456, -122.1312
reporter1.Unsubscribe();
// FixedGPS unsubscribed.
provider.TrackLocation(new Location(47.6677, -122.1199));
// MobileGPS: The current location is 47.6677, -122.1199
provider.TrackLocation(null);
// MobileGPS: The location cannot be determined.
provider.EndTransmission();
// MobileGPS unsubscribed.
// The Location Tracker has completed transmitting data to MobileGPS.
}
}
// 위치 정보를 담고 있는 데이터 클래스
public struct Location
{
double lat, lon;
public Location(double latitude, double longitude)
{
lat = latitude;
lon = longitude;
}
public double Latitude
{
get { return lat; }
}
public double Longitude
{
get { return lon; }
}
}
// Provider 클래스 (등록된(subscribe) Observer에 Notification을 보낸다)
// IObservable<out T> 인터페이스는 IDisposable Subscribe(IObserver<T> observer)를 구현해야 한다.
public class LocationTracker : IObservable<Location>
{
private List<IObserver<Location>> observers;
public LocationTracker()
{
observers = new List<IObserver<Location>>();
}
// Subscribe()는 LocationTracker 클래스에서 호출되지 않는다. LocationReporter.Subscribe()에서 호출
public IDisposable Subscribe(IObserver<Location> observer)
{
if (!observers.Contains(observer))
observers.Add(observer);
return new Unsubscriber(observers, observer);
}
private class Unsubscriber : IDisposable
{
private List<IObserver<Location>> _observers;
private IObserver<Location> _observer;
public Unsubscriber(List<IObserver<Location>> observers, IObserver<Location> observer)
{
_observers = observers;
_observer = observer;
}
public void Dispose()
{
if (_observer != null && _observers.Contains(_observer))
_observers.Remove(_observer);
}
}
public void TrackLocation(Nullable<Location> loc)
{
// observers 순회하는 예 1
foreach (IObserver<Location> observer in observers)
{
if (!loc.HasValue)
observer.OnError(new LocationUnknownException());
else
observer.OnNext(loc.Value);
}
}
public void EndTransmission()
{
// observers 순회하는 예 2
foreach (IObserver<Location> observer in observers.ToArray())
if (observers.Contains(observer))
observer.OnCompleted();
observers.Clear();
}
}
// LocationTracker.TrackLocation()에 Location 정보가 없을때 보내는 예외 클래스
public class LocationUnknownException : Exception
{
internal LocationUnknownException() : base("The location cannot be determined.")
{ }
}
// Observer 클래스 (Provider에 등록(subscribe)하고 Notification을 받는다)
// IObserver<in T> 인터페이스는 아래 3개의 매소드를 구현해야 한다.
// void OnCompleted(), void OnError(Exception error), void OnNext(T value);
public class LocationReporter : IObserver<Location>
{
private IDisposable unsubscriber;
private string instName;
public LocationReporter(string name)
{
instName = name;
}
public string Name
{ get { return instName; } }
public virtual void Subscribe(IObservable<Location> provider)
{
if (provider != null)
unsubscriber = provider.Subscribe(this);
}
public virtual void OnCompleted()
{
Unsubscribe();
Console.WriteLine("The Location Tracker has completed transmitting data to {0}.", Name);
}
public virtual void OnError(Exception e)
{
Console.WriteLine("{0}: {1}", Name, e.Message);
}
public virtual void OnNext(Location value)
{
Console.WriteLine("{2}: The current location is {0}, {1}", value.Latitude, value.Longitude, Name);
}
public virtual void Unsubscribe()
{
unsubscriber.Dispose();
Console.WriteLine("{0} unsubscribed.", Name);
}
}
}
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