Observer_Exercise.cs

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using System;
 
namespace DesignPatternExamples_csharp
{
    internal class Observer_Exercise
    {
        // ! [Using Observer in C#]
        public void Run()
        {
            Console.WriteLine();
            Console.WriteLine("Observer Exercise");
 
            ObserverSubject_NumberProducer numberProducer = new ObserverSubject_NumberProducer();
 
            // The number producer is passed to the observers so the observers
            // can get the number to display.  The observers only see the
            // INumberProducer interface, to minimize knowledge about the
            // Subject.
            ObserverForDecimal observerDecimal = new ObserverForDecimal(numberProducer);
            ObserverForHexaDecimal observerHexadecimal = new ObserverForHexaDecimal(numberProducer);
            ObserverForBinary observerBinary = new ObserverForBinary(numberProducer);
 
            // Tell the number producer about the observers who are notified
            // whenever the value changes.
            IEventNotifications eventNotifier = numberProducer as IEventNotifications;
            eventNotifier.SubscribeToNumberChanged(observerDecimal);
            eventNotifier.SubscribeToNumberChanged(observerHexadecimal);
            eventNotifier.SubscribeToNumberChanged(observerBinary);
 
            // Call the number producer's Update() method a number of times.
            // The observers automatically print out the current value in
            // different bases.
            for (int index = 0; index < 10; ++index)
            {
                Console.WriteLine("  Update {0} on number producer.  Results from observers:", index);
                numberProducer.Update();
            }
 
            // When done, remove the observers from the number producer.
            // It's always good to clean up after ourselves.
            eventNotifier.UnsubscribeFromNumberChanged(observerDecimal);
            eventNotifier.UnsubscribeFromNumberChanged(observerHexadecimal);
            eventNotifier.UnsubscribeFromNumberChanged(observerBinary);
 
            Console.WriteLine("  Done.");
        }
        // ! [Using Observer in C#]
    }
}