Observer_Exercise.cpp

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#include <iostream>
 
#include "helpers/formatstring.h"
 
#include "Observer_Exercise.h"
#include "Observer_Class.h"
 
 
namespace DesignPatternExamples_cpp
{
 
    // ! [Using Observer in C++]
    void Observer_Exercise()
    {
        std::cout << std::endl;
        std::cout << "Observer Exercise" << std::endl;
 
        INumberProducer::shared_ptr_t numberProducer = std::make_shared<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.
        IObserverNumberChanged::shared_ptr_t observerDecimal = std::make_shared<ObserverForDecimal>(numberProducer);
        IObserverNumberChanged::shared_ptr_t observerHexadecimal = std::make_shared<ObserverForHexaDecimal>(numberProducer);
        IObserverNumberChanged::shared_ptr_t observerBinary = std::make_shared<ObserverForBinary>(numberProducer);
 
        // Tell the number producer about the observers who are notified
        // whenever the value changes.
        IEventNotifications* eventNotifier = dynamic_cast<IEventNotifications*>(numberProducer.get());
        if (eventNotifier != nullptr)
        {
            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)
        {
            std::cout
                << Helpers::formatstring("  Update %d on number producer.  Results from observers:", index)
                << std::endl;
            numberProducer->Update();
        }
 
        if (eventNotifier != nullptr)
        {
            // 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);
        }
 
        std::cout << "  Done." << std::endl;
    }
    // ! [Using Observer in C++]
 
} // end namespace