lesson_2

README.md

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+Паттерн "Наблюдатель" определяет отношение "один-ко-многим" между объектами таким образом, что при изменении состояния одного объекта происходит автоматическое оповещение и обновление всех зависимых объектов.
+
+При использовании паттерна возможен как запрос, так и активная доставка данных от субъекта (запрос считается более "правильным").
+
+*Принцип:*
+- Слабосвязанные структуры более гибки и лучше выдерживают изменения.

lesson_2/CurrentConditionsDisplay.hpp

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+/*
+ * CurrentConditionsDisplay.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+#include "Observer.hpp"
+#include "DisplayElement.hpp"
+#include "WeatherData.hpp"
+
+class CurrentConditionsDisplay: public Observer, public DisplayElement
+{
+private:
+    float temperature;
+    float humidity;
+    WeatherData &weatherData;
+public:
+    CurrentConditionsDisplay(WeatherData &weatherData) :
+        temperature(0.0), humidity(0.0), weatherData(weatherData)
+    {
+        weatherData.registerObserver(*this);
+    }
+
+    void update(float temperature, float humidity, float pressure) override
+    {
+        this->temperature = temperature;
+        this->humidity = humidity;
+        display();
+    }
+
+    void display() const override
+    {
+        std::cout << "Current conditions: " << temperature << "F degrees and " << humidity << "% humidity" << std::endl;
+    }
+};

lesson_2/DisplayElement.hpp

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+/*
+ * DisplayElement.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+class DisplayElement
+{
+public:
+    virtual void display() const = 0;
+
+    virtual ~DisplayElement() {}
+};

lesson_2/ForecastDisplay.hpp

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+/*
+ * ForecastDisplay.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+#include "Observer.hpp"
+#include "DisplayElement.hpp"
+#include "WeatherData.hpp"
+
+class ForecastDisplay: public Observer, public DisplayElement
+{
+private:
+    float currentPressure;
+    float lastPressure;
+    WeatherData &weatherData;
+public:
+    ForecastDisplay(WeatherData &weatherData) :
+        currentPressure(29.92), lastPressure(0.0), weatherData(weatherData)
+    {
+        weatherData.registerObserver(*this);
+    }
+
+    void update(float temperature, float humidity, float pressure) override
+    {
+        this->lastPressure = this->currentPressure;
+        this->currentPressure = pressure;
+
+        display();
+    }
+
+    void display() const override
+    {
+        std::cout << "Forecast: ";
+        if (currentPressure > lastPressure) {
+            std::cout << "Improving weather on the way!";
+        } else if (currentPressure == lastPressure) {
+            std::cout << "More of the same";
+        } else if (currentPressure < lastPressure) {
+            std::cout << "Watch out for cooler, rainy weather";
+        }
+        std::cout << std::endl;
+    }
+};

lesson_2/HeatIndexDisplay.hpp

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+/*
+ * HeatIndexDisplay.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+#include "Observer.hpp"
+#include "DisplayElement.hpp"
+#include "WeatherData.hpp"
+
+class HeatIndexDisplay: public Observer, public DisplayElement
+{
+private:
+    float heatIndex;
+    WeatherData &weatherData;
+
+    float computeHeatIndex(float t, float rh)
+    {
+        float index = (float) ((16.923 + (0.185212 * t) + (5.37941 * rh) - (0.100254 * t * rh) + (0.00941695 * (t * t)) + (0.00728898 * (rh * rh))
+                + (0.000345372 * (t * t * rh)) - (0.000814971 * (t * rh * rh)) + (0.0000102102 * (t * t * rh * rh)) - (0.000038646 * (t * t * t))
+                + (0.0000291583 * (rh * rh * rh)) + (0.00000142721 * (t * t * t * rh)) + (0.000000197483 * (t * rh * rh * rh))
+                - (0.0000000218429 * (t * t * t * rh * rh)) + 0.000000000843296 * (t * t * rh * rh * rh))
+                - (0.0000000000481975 * (t * t * t * rh * rh * rh)));
+        return index;
+    }
+public:
+    HeatIndexDisplay(WeatherData &weatherData) : heatIndex(0.0), weatherData(weatherData)
+    {
+        weatherData.registerObserver(*this);
+    }
+
+    void update(float temperature, float humidity, float pressure) override
+    {
+        heatIndex = computeHeatIndex(temperature, humidity);
+
+        display();
+    }
+
+    void display() const override
+    {
+        std::cout << "Heat index is " << heatIndex << std::endl;
+    }
+};

lesson_2/Observer.hpp

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+/*
+ * Observer.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+class Observer
+{
+public:
+    virtual void update(float temp, float humidity, float pressure) = 0;
+
+    virtual ~Observer() {}
+};

lesson_2/StaticDisplay.hpp

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+/*
+ * StaticDisplay.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#include "Observer.hpp"
+#include "DisplayElement.hpp"
+#include "WeatherData.hpp"
+
+class StaticDisplay: public Observer, public DisplayElement
+{
+private:
+    float maxTemp;
+    float minTemp;
+    float tempSum;
+    int numReadings;
+    WeatherData &weatherData;
+public:
+    StaticDisplay(WeatherData &weatherData) :
+        maxTemp(0.0), minTemp(200.0), tempSum(0.0), numReadings(0), weatherData(weatherData)
+    {
+        weatherData.registerObserver(*this);
+    }
+
+    void update(float temperature, float humidity, float pressure) override
+    {
+        this->tempSum += temperature;
+        this->numReadings++;
+
+        if (temperature > this->maxTemp) {
+            this->maxTemp = temperature;
+        }
+
+        if (temperature < this->minTemp) {
+            this->minTemp = temperature;
+        }
+
+        display();
+    }
+
+    void display() const override
+    {
+        std::cout << "Avg/Max/Min temperature = " << (tempSum / numReadings)
+            << "/" << maxTemp << "/" << minTemp << std::endl;
+    }
+};

lesson_2/Subject.hpp

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+/*
+ * Subject.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+#include "Observer.hpp"
+
+class Subject
+{
+public:
+    virtual void registerObserver(Observer &o) = 0;
+    virtual void removeObserver(Observer &o) = 0;
+    virtual void notifyObservers() = 0;
+
+    virtual ~Subject() {}
+};

lesson_2/WeatherData.hpp

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+/*
+ * WeatherData.hpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#pragma once
+
+#include "Subject.hpp"
+#include <list>
+#include <functional>
+#include <iostream>
+
+class WeatherData: public Subject
+{
+private:
+    std::list<std::reference_wrapper<Observer>> observers;
+    float temperature;
+    float humidity;
+    float pressure;
+public:
+    void registerObserver(Observer &o) override
+    {
+        observers.push_back(o);
+    }
+
+    void removeObserver(Observer &o) override
+    {
+        observers.erase(std::find_if(observers.cbegin(), observers.cend(), [&](const std::reference_wrapper<Observer> &item)
+        {
+            return &item.get() == &o;
+        }));
+        std::cout << "Осталось в листе: " << observers.size() << " элементов" << std::endl;
+    }
+
+    void notifyObservers() override
+    {
+        for (Observer &observer : observers)
+        {
+            observer.update(temperature, humidity, pressure);
+        }
+    }
+
+    void measurementsChanged()
+    {
+        notifyObservers();
+    }
+
+    void setMeasurements(float temperature, float humidity, float pressure)
+    {
+        this->temperature = temperature;
+        this->humidity = humidity;
+        this->pressure = pressure;
+        measurementsChanged();
+    }
+
+    float getTemperature()
+    {
+        return temperature;
+    }
+
+    float getHumidity()
+    {
+        return humidity;
+    }
+
+    float getPressure()
+    {
+        return pressure;
+    }
+};

lesson_2/main.cpp

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+/*
+ * main.cpp
+ *
+ *  Created on: 31 окт. 2021 г.
+ *      Author: alexander
+ */
+
+#include "WeatherData.hpp"
+#include "CurrentConditionsDisplay.hpp"
+#include "StaticDisplay.hpp"
+#include "ForecastDisplay.hpp"
+#include "HeatIndexDisplay.hpp"
+
+int main()
+{
+    WeatherData weatherData;
+    CurrentConditionsDisplay currentDisplay(weatherData);
+    StaticDisplay staticDisplay(weatherData);
+    ForecastDisplay forecastDisplay(weatherData);
+    HeatIndexDisplay heatIndexDisplay(weatherData);
+
+    weatherData.setMeasurements(80, 65, 30.4f);
+    weatherData.setMeasurements(82, 70, 29.2f);
+    weatherData.setMeasurements(78, 90, 29.2f);
+
+    return 0;
+}
+

lesson_2/scheme

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+// interface
+
+class Subject
+{
+public:
+    virtual void registerObserver() = 0;
+    virtual void removeObserver() = 0;
+    virtual void notifyObserver() = 0;
+};
+
+class Observer
+{
+public:
+    virtual void update() = 0;
+};
+
+// classes
+
+class ConcreteSubject : public Subject
+{
+public:
+    void getState();
+    void setState();
+};
+
+class ConcreteObserver : public Observer
+{
+public:
+};