ObserverSubject_NumberProducer.cs

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using System.Collections.Generic;
 
namespace DesignPatternExamples_csharp
{
    public interface IObserverNumberChanged
    {
        void NumberChanged();
    }
 
 
    //########################################################################
    //########################################################################
 
 
    public interface IEventNotifications
    {
        void SubscribeToNumberChanged(IObserverNumberChanged observer);
        void UnsubscribeFromNumberChanged(IObserverNumberChanged observer);
    }
 
 
    //########################################################################
    //########################################################################
 
 
    public interface INumberProducer
    {
        uint FetchNumber();
    }
 
 
    //########################################################################
    //########################################################################
 
 
    class ObserverSubject_NumberProducer : IEventNotifications, INumberProducer
    {
        private List<IObserverNumberChanged> _observers = new List<IObserverNumberChanged>();
 
        private uint _number;
 
 
        void _NotifyNumberChanged()
        {
            // Copy the list so observers can change the original observers
            // during the notification (this isn't strictly needed in this
            // example but it is good practice for any notification system
            // that handles multiple observers where multiple threads might
            // be in play or observers can unsubscribe at any time, even in
            // the event notification).
            IObserverNumberChanged[] observers = _observers.ToArray();
 
            foreach(IObserverNumberChanged observer in observers)
            {
                observer.NumberChanged();
            }
        }
 
 
        public void Update()
        {
            ++_number;
            _NotifyNumberChanged();
        }
 
 
        //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        // Implementation of the INumberProducer interface.
        //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
        uint INumberProducer.FetchNumber()
        {
            return _number;
        }
 
 
        //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        // Implementation of the IEventNotifications interface.
        //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
        void IEventNotifications.SubscribeToNumberChanged(IObserverNumberChanged observer)
        {
            if (!_observers.Contains(observer))
            {
                _observers.Add(observer);
            }
        }
 
 
        void IEventNotifications.UnsubscribeFromNumberChanged(IObserverNumberChanged observer)
        {
            if (_observers.Contains(observer))
            {
                _observers.Remove(observer);
            }
        }
    }
}