C + + design mode-Viewer mode

Observer pattern: It defines a dependency on the elephant's leisure, so that when a likeness is changed, all of its dependent people are notified and updated on their own, too.

The graph of the Observer pattern:

code example: using the Weatherdata to obtain the figures, update the concreteobserver and show that the following is the code example:

1 #ifndef Subject_h2 #defineSubject_h3#include"Observer.h"4 classsubject5 {6  Public:7 subject ();8     Virtual~subject ();9     Virtual voidRegisterobserver (observer* o) =0;Ten     Virtual voidRemoveobserver (observer* o) =0; One     Virtual voidNotifyobservers () =0; A }; -  - #endif //Subject_h

Subject

1 #ifndef Observer_h2 #defineObserver_h3 4 classObserver5 {6  Public:7 Observer ();8     Virtual~Observer ();9     Virtual voidUpdatefloatTempfloatHumidity,floatpressure) =0;Ten  One }; A  - #endif //Observer_h

Observer

1#include"weather_data.h"2 3 Weatherdata::weatherdata ()4 {5 m_vecobserver.clear ();6 }7weatherdata::~Weatherdata ()8 {9 Ten } One  A voidWeatherdata::registerobserver (Observer *o) - { - m_vecobserver.append (o); the  - } -  - voidWeatherdata::removeobserver (observer*o) + { -   intindex =M_vecobserver.indexof (o); +   if(Index >=0) A   { at M_vecobserver.remove (index); -   } - } -  - voidweatherdata::notifyobservers () - { in      for(inti =0; i < m_vecobserver.size (); i++) -     { tom_vecobserver.at (i)->update ( This->temperature, This->humidity, This-pressure); +     } - } the  * voidWeatherdata::setmeasurements (floatTemperature,floatHumidity,floatpressure) $ {Panax Notoginseng      This->temperature =temperature; -      This->humidity =humidity; the      This->pressure =pressure; + measurementschanged (); A } the floatweatherdata::gettemperature () + { -     return  This-temperature; $ } $  - floatweatherdata::gethumidity () - { the     return  This-humidity; - }Wuyi  the floatweatherdata::getpressure () - { Wu     return  This-pressure; - } About  $ voidweatherdata::measurementschanged () - { - notifyobservers (); -}

Weather_data

1#include"Concreteobserver.h"2#include <QDebug>3#include <weather_data.h>4Concreteobserver::concreteobserver (Subject *weatherdata)5 {6      This->weatherdata =Weatherdata;7Weatherdata->registerobserver ( This);8 9 }Ten  One voidConcreteobserver::update (floatTempfloatHumidity,floatpressure) A { -      This->temperature =temp; -      This->humidity =humidity; the display (); - } -  - voidconcreteobserver::d isplay () + { -Qdebug () <<"when the temperature of the former:"<< This->temperature<<"Pre-elevation:"<< This-humidity; +}

Concreteobserver

1#include <QCoreApplication>2#include"Concreteobserver.h"3#include"weather_data.h"4 intMainintargcChar*argv[])5 {6 qcoreapplication A (argc, argv);7weatherdata* subject =NewWeatherdata ();8concreteobserver* Observer =NewConcreteobserver (subject);9Subject->setmeasurements ( -, -, +);TenSubject->setmeasurements ( +, -, -); One  A  -     returna.exec (); -}

Main

Reference information: Headfirst design mode

Source code:

C + + design mode-Viewer mode