[toc]

观察者模式定义

观察者模式定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有依赖者都会收到通知并自动更新。

气象站布告板设计

  1. #include <utility>
  2. #include "algorithm"
  3. #include "iostream"
  4. #include "vector"
  5. using namespace std;
  7. class Observer {
  8. public:
  9.     // 所有的观察者都必须实现update方法
  10.     virtual void update(float temp, float humidity, float pressure){};
  11. };
  12. class Subject {
  13. public:
  14.                                                                                                                                          virtual void registerObserver(Observer *o) {}
  15.     virtual void removeObserver(Observer *o) {}
  16.     virtual void notifyObserver() {} // 主题改变时调用次方法，以通知所有的观察者
  17. };
  18. class DisplayElement {
  19.     virtual void display() {}
  20. };       
  22. // weatherdata 需要实现Subject接口
  23. class WeatherData : public Subject {
  24. private:
  25.     vector<Observer *> observers;
  26.     float temperature{};
  27.     float humidity{};
  28.     float pressure{};
  30. public:
  31.     WeatherData() = default;
  32.     void registerObserver(Observer *o) override { observers.push_back(o); }
  33.     void removeObserver(Observer *o) override {
  34.         for (auto iter = observers.begin(); iter != observers.end(); iter++) {
  35.             if (*iter == o) {
  36.                 observers.erase(iter, iter + 1);
  37.                 break;
  38.             }
  39.         }
  40.     }
  41.     void notifyObserver() override {
  42.         for (auto ob : observers) {
  43.             ob->update(temperature, humidity, pressure);
  44.         }
  45.     }
  46.     void measurementsChanged(float temp,float humi,float pressure) {
  47.         this->temperature=temp;
  48.         this->humidity=humi;
  49.         this->pressure=pressure;
  50.         notifyObserver();
  51.     }
  52. };
  54. class CurrentConditionDisplay : public Observer, DisplayElement {
  55. private:
  56.     float temperature{};
  57.     float humidity{};
  58.     Subject *weatherData;
  60. public:
  61.     explicit CurrentConditionDisplay(Subject *wethData) {
  62.         weatherData = wethData;
  63.         weatherData->registerObserver(this);
  64.     }
  65.     void update(float temp, float humidity, float pressure) override {
  66.         this->temperature=temp;
  67.         this->humidity=humidity;
  68.         display();
  69.     }
  70.     void display() override {
  71.         cout<<"Current Condition: "<<temperature<<"F "<<" and "<<humidity<<endl;
  72.     }
  73. };
  75. class StatisticsDisplay : public Observer, DisplayElement {
  76. private:
  77.     float temperature{};
  78.     float humidity{};
  79.     Subject *weatherData;
  81. public:
  82.     explicit StatisticsDisplay(Subject *wethData) {
  83.         weatherData = wethData;
  84.         weatherData->registerObserver(this);
  85.     }
  86.     void update(float temp, float humidity, float pressure) override {
  87.         this->temperature=temp;
  88.         this->humidity=humidity;
  89.         display();
  90.     }
  91.     void display() override {
  92.         cout<<"Statics Condition: "<<temperature<<"F "<<" and "<<humidity<<endl;
  93.     }
  94. };
  98. int main() {
  99.     cout << ">>>>>>>>>>>>>>>>>RUNNING on CLion<<<<<<<<<<<<<" << endl;
  100.     auto *weatherData=new WeatherData();
  101.     auto *currentDisplay=new CurrentConditionDisplay(weatherData);
  102.     auto *staticsDisplay=new StatisticsDisplay(weatherData);
  103.     weatherData->measurementsChanged(80,65,30.4);
  104.     weatherData->measurementsChanged(82,70,29.3);
  105.     weatherData->measurementsChanged(78,90,28.3);
  107.     return 0;
  108. }