（转）设计模式--观察者模式

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。 

博客类中有一个观察者链表（即订阅者），当博客的状态发生变化时，通过Notify成员函数通知所有的观察者，告诉他们博客的状态更新了。而观察者通过Update成员函数获取博客的状态信息。 

#include <iostream>
#include <string>
#include <list>

using namespace std;

//观察者
class Observer
{
public:
	Observer(){}
	virtual ~Observer(){}
	virtual void Update(){}
};
//博客
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 string GetStatus(){ return m_status; }
private:
	list<Observer*> m_observers;
protected:
	string m_status;
};
//具体博客类
class BlogCSDN : public Blog
{
private:
	string m_name; //博主名称
public:
	BlogCSDN(string name) : m_name(name) {}
	~BlogCSDN() {}
	void SetStatus(string s) { m_status = "CSDN通知 : " + m_name + s; } //具体设置状态信息
	string GetStatus() { return m_status; }
};
//具体观察者
class ObserverBlog : public Observer
{
private:
	string m_name;  //观察者名称
	Blog *m_blog;   //观察的博客，当然以链表形式更好，就可以观察多个博客
public:
	ObserverBlog(string name, Blog *blog) : m_name(name), m_blog(blog) {}
	~ObserverBlog() {}
	void Update()  //获得更新状态
	{
		string status = m_blog->GetStatus();
		cout << m_name << "-------" << status << endl;
	}
};
//测试案例
int main()
{
	Blog *blog = new BlogCSDN("wuzhekai1985");
	Observer *observer1 = new ObserverBlog("tutupig", blog);
	blog->Attach(observer1);
	blog->SetStatus("发表设计模式C++实现（15）——观察者模式");
	blog->Notify();
	delete blog; 
	delete observer1;
	system("Pause");
	return 0;
}

#include <iostream>
#include <string>
#include <list>

using namespace std;

//创建观察者接口
class TeacherListenner
{
public:
	virtual void onTeacherComming() = 0;
};

//创建被观察者借口
class iNotifier
{
public:
	virtual void addListenner(TeacherListenner *listenner) = 0;
	virtual void removeListenner(TeacherListenner *listenner) = 0;
	virtual void notify() = 0;
};

//创建具体被观察者
class TeacherNotify :public iNotifier
{
public:
	void addListenner(TeacherListenner *listenner)
	{
		m_list.push_back(listenner);
	}
	void removeListenner(TeacherListenner *listenner)
	{
		m_list.remove(listenner);
	}
	void notify()
	{
		for (list<TeacherListenner*>::iterator it = m_list.begin(); it != m_list.end(); ++it)
		{
			(*it)->onTeacherComming();
		}
	}
private:
	list<TeacherListenner*> m_list;
};
//创建具体观察者
class Xiaozhang : public TeacherListenner
{
public:
	void onTeacherComming()
	{
		cout << "老师来了" << endl;
	}
};
class Xiaoli : public TeacherListenner
{
public:
	void onTeacherComming()
	{
		cout << "老师来了" << endl;
	}
};

int main()
{
	TeacherNotify monitor;
	Xiaoli xl;
	Xiaozhang xz;
	monitor.addListenner(&xl);
	monitor.addListenner(&xz);

	monitor.notify();
	xl.onTeacherComming();
	xz.onTeacherComming();
	system("Pause");
	return 0;
}