C++实现观察者模式.docx

观察者模式是大学阶段应该掌握的几种重要的模式之一，它的用处广泛，而且其变种更能解决许多实际问题。下面详细的介绍一下。名称：观察者模式-Observer别名：Dependents, Publish-Subscribe意图：定义对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。下面用一个教师-学生的例子说明观察者模式，其中学生是观察者，教师是被观察者，不过这个也适用于电器-开关的例子，可以把电器看作观察者，开关看作被观察者，当开关开始有动作的时候，观察者接收到信息：/-/ Subject.h 被观察对象/-#ifndef SUBJECT_H#define SUBJECT_H#include Observer.hclass Observer;class Subjectpublic: virtual Subject() virtual void Attach(Observer *aObserver) = 0; virtual void Talk() = 0; virtual char *GetContent() const = 0; virtual void SetContent(char *aContent) = 0;protected: Subject();#endif/-/ Teacher.h/-#ifndef TEACHER_H#define TEACHER_H#include Subject.h#include #include class Teacher : public Subjectpublic: Teacher(); virtual void Attach(Observer *aObserver); virtual void Talk(); virtual char *GetContent() const; virtual void SetContent(char *aContent);private: std:list observerList; char *content;#endif;/-/ Teacher.cpp/-#include Teacher.hTeacher:Teacher() content = 现在开始上课;void Teacher:Attach(Observer *aObserver) observerList.push_back(aObserver);void Teacher:SetContent(char *aContent) content = aContent;void Teacher:Talk() std:list:iterator students; for(students = observerList.begin() ; students != observerList.end() ; +students) (Observer *)(*students)-Listen(this); char *Teacher:GetContent() const return content;/-/ Observer.h 观察者/-#ifndef OBSERVER_H#define OBSERVER_H#include Subject.hclass Subject;class Observerpublic: virtual void Listen(Subject *aSubject) = 0; virtual Observer()protected: Observer();#endif/-/ Student.h/-#ifndef STUDENT_H#define STUDENT_H#include Observer.hclass Student : public Observerpublic: Student(char* = 学生); char *GetName() const; virtual void Listen(Subject *aSubject);private: char *name;#endif/-/ Student.cpp/-#include #include Student.hStudent:Student(char *aName) name = aName;void Student:Listen(Subject *aSubject) std:cout GetName() :老师刚才说， GetContent() std:endl;char *Student:GetName() const return name;/-/ demo.cpp/-#include Student.h#include Teacher.hint main() Student *student1 = new Student(张三); Student *student2 = new Student(李四); Student *student3 = new Student(王五); Teacher teacher; teacher.Attach(student1); teacher.Attach(student2); teacher.Attach(