C++----設計模式之觀察者模式

觀察者設計模式定義了對象間的一對多的依賴關係，一個對象的行爲依賴於另一個對象的狀態的情況下，當對象狀態發生變化時，依賴它的對象會得到通知並自動刷新。

觀察者模式中主要有兩種角色：觀察者和監聽者

觀察者主要是在事件到來時， 通知對於該事件感興趣的監聽者來處理事件。所以它的職責也就顯而易見了：①通知觀察者；②註冊事件。那麼監聽者當然就是來處理事件的了。

接下來通過代碼實現一個簡單的觀察者模式~

#include<iostream>
#include<string>

class Listerner			//定義監聽者類
{
public:
	Listerner(std::string name) :mname(name) {}
	virtual void handleMessage(int message)const = 0;
protected:
	std::string mname;
};

class Listerner1 : public Listerner		//定義1號監聽者
{
public:
	Listerner1(std::string name) :Listerner(name) {}
	virtual void handleMessage(int message)const
	{
		switch (message)
		{
		case 1:
			std::cout << mname << " has been solved message 1" << std::endl;
			break;
		case 2:
			std::cout << mname << " has been solved message 2" << std::endl;
			break;
		default:
			std::cout << mname << " no interested this message" << std::endl;
			break;
		}
	}
};
class Listerner2 : public Listerner				//定義2號監聽者
{
public:
	Listerner2(std::string name) :Listerner(name) {}
	virtual void handleMessage(int message)const
	{
		switch (message)
		{
		case 1:
			std::cout << mname << " has been solved message 1" << std::endl;
			break;
		case 2:
			std::cout << mname << " has been solved message 2" << std::endl;
			break;
		default:
			std::cout << mname << " no interested this message" << std::endl;
			break;
		}
	}
};
class Listerner3 : public Listerner				//定義3號監聽者
{
public:
	Listerner3(std::string name) :Listerner(name) {}
	virtual void handleMessage(int message)const
	{
		switch (message)
		{
		case 1:
			std::cout << mname << " has been solved message 1" << std::endl;
			break;
		case 2:
			std::cout << mname << " has been solved message 2" << std::endl;
			break;
		default:
			std::cout << mname << " no interested this message" << std::endl;
			break;
		}
	}
};


#include<map>
#include<vector>

/*
	multimap   一對多
		map	   一對一個集合
*/

class Obeserve				//定義觀察者
{
public:
	typedef std::map<int, std::vector<const Listerner*>> Mty;
	typedef std::vector<const Listerner*> Vty;
	void registerMessage(int message, const Listerner* pls)
	{
		Mty::iterator fit = mymap.find(message);
		if (fit != mymap.end())
		{
			fit->second.push_back(pls);
		}
		else
		{
			Vty vec;
			vec.push_back(pls);
			mymap[message] = vec;
		}
	}
	void notify(int message)
	{
		Mty::iterator fit = mymap.find(message);
		if (fit != mymap.end())
		{
			Vty::iterator it = fit->second.begin();
			while (it != fit->second.end())
			{
				(*it)->handleMessage(message);
				it++;
			}
		}
	}
private:
	std::map<int, std::vector<const Listerner*>> mymap;
};

int main()
{
	Listerner1 l1("listerner1");
	Listerner2 l2("listerner2");
	Listerner3 l3("listerner3");

	Obeserve ob;
	ob.registerMessage(1, &l1);
	ob.registerMessage(2, &l1);
	ob.registerMessage(2, &l2);
	ob.registerMessage(3, &l2);
	ob.registerMessage(1, &l3);
	ob.registerMessage(3, &l3);

	ob.notify(2);
	return 0;
}

運行結果：