基于C++实现观察者模式

1.观察者模式

观察者模式：定义一种一（被观察）对多（观察）的关系。在被观察类发生某种事件时，观察类需要做出反应。

实现方式：

在被观察者类里定义一个表示状态的变量，然后在观察者类里存放一个被观察者类对象，通过被观察者类对象获取状态。同时，被观察者类使用vector/list .... 来管理观察者。

2.看看代码吧

cpp 复制代码

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

using namespace std;

//观察者类
class Observer {
public:
	Observer() {}
	virtual ~Observer() {}
	virtual void update() {}
};


class SubObject
{
public:
	string _action; //设置状态
	SubObject() {}
	virtual ~SubObject() {}

	//添加观察者
	void attach(Observer* ob)
	{
		ls.push_back(ob);
	}
	//去除观察者
	void detach(Observer* ob)
	{
		ls.remove(ob);
	}
	//通知
	void notify()
	{
		for (auto e : ls)
		{
			e->update();
		}
	}

	//设置状态
	virtual void SetAction(string action) {
		_action = action;
	}
	//返回状态
	virtual string GetAction() {
		return _action;
	}
protected:
	list<Observer*> ls;
};

class BossObject : public SubObject
{
public:
	BossObject()		
	{}
	void SetAction(string action) {
		_action = action;
	}
	string GetAction() {
		return _action;
	}
};

class SleepObserver : public Observer
{
public:
	SleepObserver(string name, SubObject* sub)
		:_sub(sub), _name(name)
	{}

	void update()
	{
		string action = _sub->GetAction();
		cout << "我是观察者: " << _name << endl;
		cout << "老板说:" << action << endl;

		if (action == "sleep")
			cout << "我要睡大觉咯" << endl;
	}

private:
	SubObject* _sub;
	string _name;
};

class WorkObserver : public Observer
{
public:
	WorkObserver(string name, SubObject* sub)
		:_sub(sub), _name(name)
	{}

	void update()
	{
		string action = _sub->GetAction();
		cout << "我是观察者: " << _name << endl;
		cout << "老板说:" << action << endl;

		if (action == "work")
			cout << "我要努力加班，努力搞$" << endl;
	}

private:
	SubObject* _sub;
	string _name;
};

int main()
{
	SubObject* Boss = new BossObject();
	SleepObserver* ob1 = new SleepObserver("sleepob", Boss);
	WorkObserver* ob2 = new WorkObserver("workob", Boss);

	Boss->attach(ob1);
	Boss->attach(ob2);

	Boss->SetAction("work");
	Boss->notify();
	cout << endl;

	Boss->SetAction("sleep");
	Boss->notify();
	cout << endl;

	return 0;
}

结果图：