平面设计线上培训机构推荐_社交新零售_推广网站的方法有哪些_刷seo排名

一、组成

抽象主题：维护观察者对象列表，具备通知功能。
具体主题：实现维护观察者对象列表具体策略和通知功能。
抽象观察者：为主题类提供更新接口。
具体观察者：实现更新接口。

二、目的

用于一个对象状态发生变化，所有依赖于它的对象都自动收到通知并进行更新。

三、缺点

1、资源浪费问题，存在大量观察者时，通知所有观察者会导致不需要此消息的观察者也收到这个消息。
2、通知顺序不确定，如果观察者之间需要存在先后收到通知的依赖关系时会有问题、

四、示例代码

#include<iostream>
#include <vector>
#include <string>
using namespace std;class WeatherObserver;//抽象观察者类
class WeatherApp;//具体观察者类
class AbstractWeatherStation;//抽象主题类
class WeatherStation;//具体主题类class WeatherObserver {
public:virtual void updateWeather(const string weatherName) = 0;
};class WeatherApp :public WeatherObserver {
public:explicit WeatherApp(const string appName) :appName(appName) {};void updateWeather(const string weatherName) {weatherCur = weatherName;printCurWeather();}void printCurWeather() {cout << "The current weather on thre " << appName << " app is " << weatherCur << endl;}
private:string weatherCur;string appName;
};class AbstractWeatherStation {
public:virtual void addObserver(shared_ptr<WeatherObserver> observer) = 0;virtual void removeObserver(shared_ptr<WeatherObserver> observer) = 0;virtual void notifyObservers() = 0;
protected:vector<shared_ptr<WeatherObserver>> observers;
};class WeatherStation :public AbstractWeatherStation {
public:void addObserver(shared_ptr<WeatherObserver> observer) {observers.push_back(observer);}void removeObserver(shared_ptr<WeatherObserver> observer) {observers.erase(remove(observers.begin(), observers.end(), observer), observers.end());}void notifyObservers() {for (const auto& observer : observers) {observer->updateWeather(weatherCur);}}void updateWeather(const string& weather) {weatherCur = weather;notifyObservers();}
private:vector<shared_ptr<WeatherObserver>> observers;string weatherCur;
};int main() {shared_ptr<WeatherObserver> app1 = make_shared<WeatherApp>("天气宝app");shared_ptr<WeatherObserver> app2 = make_shared<WeatherApp>("气象通app");shared_ptr<WeatherStation> weatherStation = make_shared<WeatherStation>();weatherStation->addObserver(app1);weatherStation->addObserver(app2);weatherStation->updateWeather("晴天");weatherStation->removeObserver(app1);weatherStation->updateWeather("雨天");}