C++設計模式——觀察者模式

觀察者模式：定義了對象之閒的一對多依賴，這樣一來，儅一個對象改變狀態時，它的所有依賴者都會收到通知並自動更新。

觀察者模式的類圖：

代碼示例：利用WeatherData對象取得數據，更新concreteobserver 並顯示出來，以下是代碼示例：

 1 #ifndef SUBJECT_H
 2 #define SUBJECT_H
 3 #include "observer.h"
 4 class subject
 5 {
 6 public:
 7     subject();
 8     virtual ~subject();
 9     virtual void registerObserver(Observer* o) = 0;
10     virtual void removeObserver(Observer* o)= 0;
11     virtual void notifyObservers() = 0;
12 };
13 
14 #endif // SUBJECT_H

Subject

 1 #ifndef OBSERVER_H
 2 #define OBSERVER_H
 3 
 4 class Observer
 5 {
 6 public:
 7     Observer();
 8     virtual ~Observer();
 9     virtual void update(float temp,float humidity,float pressure) = 0;
10 
11 };
12 
13 #endif // OBSERVER_H

Observer

 1 #include "weather_data.h"
 2 
 3 WeatherData::WeatherData()
 4 {
 5     m_vecObserver.clear();
 6 }
 7 WeatherData::~WeatherData()
 8 {
 9 
10 }
11 
12 void WeatherData::registerObserver(Observer *o)
13 {
14     m_vecObserver.append(o);
15 
16 }
17 
18 void WeatherData::removeObserver(Observer* o)
19 {
20   int index =  m_vecObserver.indexOf(o);
21   if(index >=0)
22   {
23       m_vecObserver.remove(index);
24   }
25 }
26 
27 void WeatherData::notifyObservers()
28 {
29     for(int i = 0;i < m_vecObserver.size();i++)
30     {
31         m_vecObserver.at(i)->update(this->temperature,this->humidity,this->pressure);
32     }
33 }
34 
35 void WeatherData::setMeasureMents(float temperature, float humidity, float pressure)
36 {
37     this->temperature = temperature;
38     this->humidity = humidity;
39     this->pressure = pressure;
40     measurementsChanged();
41 }
42 float WeatherData::getTemperature()
43 {
44     return this->temperature;
45 }
46 
47 float WeatherData::getHumidity()
48 {
49     return this->humidity;
50 }
51 
52 float WeatherData::getPressure()
53 {
54     return this->pressure;
55 }
56 
57 void WeatherData::measurementsChanged()
58 {
59    notifyObservers();
60 }

weather_data

 1 #include "concreteobserver.h"
 2 #include <QDebug>
 3 #include <weather_data.h>
 4 ConcreteObserver::ConcreteObserver(subject *weatherData)
 5 {
 6     this->weatherData = weatherData;
 7     weatherData->registerObserver(this);
 8 
 9 }
10 
11 void ConcreteObserver::update(float temp, float humidity, float pressure)
12 {
13     this->temperature = temp;
14     this->humidity = humidity;
15     display();
16 }
17 
18 void ConcreteObserver::display()
19 {
20     qDebug()<<"當前溫度："<<this->temperature<<"當前海拔："<<this->humidity;
21 }

concreteobserver

 1 #include <QCoreApplication>
 2 #include "concreteobserver.h"
 3 #include "weather_data.h"
 4 int main(int argc, char *argv[])
 5 {
 6     QCoreApplication a(argc, argv);
 7    WeatherData* subject = new WeatherData();
 8     ConcreteObserver* observer = new ConcreteObserver(subject);
 9    subject->setMeasureMents(20,30,40);
10    subject->setMeasureMents(40,50,20);
11 
12 
13     return a.exec();
14 }

main

參考資料：HeadFirst 設計模式

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