Observer design pattern - implementation 1

CMakeLists.txt

cmake_minimum_required(VERSION 3.9)
project(observer-design-pattern1)

#====== Global Configurations ==================#

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_VERBOSE_MAKEFILE ON)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt5 COMPONENTS Core Widgets REQUIRED)

#=============== Target Configurations ============#

       add_executable( observer1 observer-pattern1.cpp )
target_link_libraries( observer1 Qt5::Core Qt5::Gui Qt5::Widgets)

observer-pattern1.cpp

#include <iostream>
#include <iomanip>

#include <QtWidgets>
#include <QApplication>
#include <QSysInfo>

struct IObserver;

struct IObservable 
{
    /** Subscribe to observable notifications */
    virtual void addObserver(IObserver* obs) = 0;

    /** Notify all observers */
    virtual void notify() = 0; 
    virtual     ~IObservable() = default;
};

struct IObserver 
{
    virtual void update(IObservable* sender) = 0;
    virtual     ~IObserver() = default;
};

class BasicObservable: public IObservable 
{
    std::vector<IObserver*> m_observers{};
public:
    
    void addObserver(IObserver* obs) override 
    {
        m_observers.push_back(obs);
        obs->update(this);
    }

    /** Notify all observers */
    void notify() override  
    {
        for(const auto obs: m_observers){ obs->update(this); }
    }    
};

class CounterModel: public BasicObservable
{
    int m_counter = 0;
public: 
    
    void increment() 
    { 
        m_counter += 1;
        this->notify();
    }
    void decrement() 
    {
        m_counter -= 1;
        this->notify();
    }
    void reset()
    { 
        m_counter = 0;  
        this->notify();
    }

    void set(int n)
    {
        m_counter = n;
        this->notify();
    }

    int get() const { return m_counter; }
};

/** Concrete observer that prints the subject state in the console (terminal) */
class ConsoleView: public IObserver 
{
    /* override: IObserver::update() */
    void update(IObservable* sender) override 
    {
        /* Note: It can result in undefined behavior. */
        int cnt = static_cast<CounterModel*>(sender)->get();
        std::cout << " [CONSOLE] Counter state changed to = " << cnt << '\n';
    }
};


class FormView: public IObserver {
    QWidget      m_win{};
    QFormLayout* m_form;
    QPushButton* m_btn_increment;
    QPushButton* m_btn_decrement;
    QLabel*      m_label;

    CounterModel& m_model;
public:

    FormView(CounterModel& model): m_model(model)
    {
        m_win.setWindowTitle("Form View");
        m_form = new QFormLayout(&m_win);
        m_btn_increment = new QPushButton("[+]");
        m_btn_decrement = new QPushButton("[-]");
        m_label         = new QLabel("0");

        m_form->addRow("Increment",     m_btn_increment);
        m_form->addRow("Decrement",     m_btn_decrement);
        m_form->addRow("Counter value", m_label);

        m_win.show(); 

        /** ------ Setup event handlers ------------------- **/

        QObject::connect(m_btn_decrement, &QPushButton::clicked, 
            [self = this]{ 
                self->m_model.decrement();
            });
        
        QObject::connect(m_btn_increment, &QPushButton::clicked, 
            [this](){ 
                m_model.increment(); 
            });
    }

    /* override: IObserver::update() */
    void update(IObservable* sender) override 
    {
        int cnt = static_cast<CounterModel*>(sender)->get();
        m_label->setText(QString::number(cnt)); 
        std::cout << " [QT GUI] Counter state changed to = " << cnt << '\n';
    }
};

class LabelView: public IObserver
{
    QLabel m_label;
public:
    LabelView() 
    {   
        m_label.setWindowTitle("Label View");
        m_label.resize(400, 300);
        m_label.show();
    }

    /* override: IObserver::update() */
    void update(IObservable* sender) override 
    {
        int cnt = static_cast<CounterModel*>(sender)->get();
        m_label.setText(" [LABEL Observer] Counter value = " + QString::number(cnt));
    }

};


int main(int argc, char** argv)
{
    // Useful for debugging
    std::cout << " [INFO] QTVersion = " << ::qVersion() << std::endl;


    QApplication app(argc, argv);

    CounterModel model;     
    ConsoleView  observerA{};
    FormView     observerB{model};
    LabelView    observerC{};

    model.addObserver(&observerA);
    model.addObserver(&observerB);
    model.addObserver(&observerC);

    return app.exec();
}