观察者模式: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。它还有两个别名,依赖 (Dependents),发布-订阅(Publish-Subsrcibe)。可以举个博客订阅的例子,当博主发表新文章的时候,即博主状态发生了改 变,那些订阅的读者就会收到通知,然后进行相应的动作,比如去看文章,或者收藏起来。博主与读者之间存在种一对多的依赖关系。下面给出相应的UML图设 计。
以博客和博客的粉丝(observer)为例
#include <iostream> #include <list> #include <string> using namespace std; class Observer { public: Observer() {} virtual ~Observer() {} virtual void Update() {} }; class Blog { public: Blog(){} virtual ~Blog() {} void Attach(Observer *observer) { m_observers.push_back(observer); } void Remove(Observer* observer) { m_observers.remove(observer); } void Notify() { list<Observer*>::iterator iter = m_observers.begin(); for(;iter != m_observers.end(); iter++) (*iter)->Update(); } virtual void SetStatus(string s) { m_status = s; } virtual std::string GetStatus() { return m_status; } private: list<Observer* > m_observers; protected: std::string m_status; }; class BlogBKY : public Blog { public: BlogBKY(string name):m_name(name) {} ~BlogBKY() {} void SetStatus(string s) { m_status = s ; } string GetStatus() { return m_status; } private: string m_name; }; class ObserverBlog : public Observer { public: ObserverBlog(string name,Blog *blog):m_name(name),m_blog(blog) { } ~ObserverBlog() {} void Update() { std::string status = m_blog->GetStatus(); cout << m_name <<"-------" << status <<endl; } private: std::string m_name; Blog *m_blog; };
接口的使用:
#include "observer.h" int main() { Blog *blog = new BlogBKY("onlycxue"); Observer *observer1 = new ObserverBlog("hello",blog); blog->Attach(observer1); blog->SetStatus("发表博客!"); blog->Notify(); system("pause"); //delete blog; //delete observer1; return 0;