行為型模式：觀察者模式

觀察者模式定義了一種一對(duì)多的依賴關(guān)系：它讓一個(gè)主題（被觀察者）對(duì)象關(guān)聯(lián)多個(gè)觀察者對(duì)象，并且當(dāng)主題對(duì)象的狀態(tài)發(fā)生變化時(shí)，它會(huì)主動(dòng)通知這些觀察者對(duì)象，使它們能夠自動(dòng)更新自己或執(zhí)行相應(yīng)的響應(yīng)操作。

以一個(gè)設(shè)備的溫度顯示系統(tǒng)為例，在這個(gè)示例中，溫度檢測儀是被觀察者，當(dāng)設(shè)備溫度發(fā)生變化時(shí)，它會(huì)通知所有的顯示器更新溫度信息。

#include <iostream>
#include <vector>
#include <string>
#include <algorithm> // 觀察者接口
class IObserver {
public:virtual void update(float temperature) = 0;virtual ~IObserver() {}
};// 主題接口（Subject）
class ISubject {
public:virtual void registerObserver(IObserver* observer) = 0;virtual void removeObserver(IObserver* observer) = 0;virtual void notifyObservers() = 0;virtual ~ISubject() {}
};// 被觀察者類：設(shè)備溫度檢測儀
class DeviceTemperatureMonitor : public ISubject {
private:std::vector<IObserver*> observers;float temperature;public:// 注冊觀察者void registerObserver(IObserver* observer) override {observers.push_back(observer);}// 移除觀察者void removeObserver(IObserver* observer) override {// std::remove將所有與指定值observer相等的元素移動(dòng)到容器的末尾，并返回指向第一個(gè)不需要保留的元素的迭代器observers.erase(std::remove(observers.begin(), observers.end(), observer), observers.end());}// 通知所有觀察者void notifyObservers() override {for (IObserver* observer : observers) {observer->update(temperature);}}// 設(shè)置溫度狀態(tài)并通知所有觀察者void setTemperature(float temp) {temperature = temp;notifyObservers();}
};// 觀察者類：手機(jī)顯示器
class PhoneDisplay : public IObserver {
private:std::string deviceName;public:PhoneDisplay(const std::string& name) : deviceName(name) {}void update(float temperature) override {std::cout << "Phone Display (" << deviceName << ") - Device Temperature: " << temperature << "°C\n";}
};// 觀察者類：窗口顯示器
class WindowDisplay : public IObserver {
private:std::string location;public:WindowDisplay(const std::string& loc) : location(loc) {}void update(float temperature) override {std::cout << "Window Display at " << location << " - Device Temperature: " << temperature << "°C\n";}
};int main() {// 創(chuàng)建被觀察者對(duì)象（設(shè)備溫度檢測儀）DeviceTemperatureMonitor tempMonitor;// 創(chuàng)建觀察者對(duì)象（顯示設(shè)備）PhoneDisplay phoneDisplay1("iPhone");PhoneDisplay phoneDisplay2("Samsung");WindowDisplay windowDisplay("Office");// 注冊觀察者tempMonitor.registerObserver(&phoneDisplay1);tempMonitor.registerObserver(&phoneDisplay2);tempMonitor.registerObserver(&windowDisplay);// 模擬溫度數(shù)據(jù)更新std::cout << "Temperature Update 1:\n";tempMonitor.setTemperature(75.0f);std::cout << "\nTemperature Update 2:\n";tempMonitor.setTemperature(80.0f);// 移除一個(gè)觀察者tempMonitor.removeObserver(&phoneDisplay2);std::cout << "\nTemperature Update 3 (After removing Samsung Phone Display):\n";tempMonitor.setTemperature(85.0f);return 0;
}

Temperature Update 1:
Phone Display (iPhone) - Device Temperature: 75°C
Phone Display (Samsung) - Device Temperature: 75°C
Window Display at Office - Device Temperature: 75°CTemperature Update 2:
Phone Display (iPhone) - Device Temperature: 80°C
Phone Display (Samsung) - Device Temperature: 80°C
Window Display at Office - Device Temperature: 80°CTemperature Update 3 (After removing Samsung Phone Display):
Phone Display (iPhone) - Device Temperature: 85°C
Window Display at Office - Device Temperature: 85°C