监听者模式（listener）(c++实现)

监听者对大家来说可能并不陌生，所谓监听者就是用来监听自已感兴趣的事件的，当收到自已感兴趣的事件时会做出相应的反映。

    它的应用是非常广的，比如win32的消息机制，它跟监听者模式就异曲同工，操作系统将产生的各种事件包装成消息(msg),该消息结构包装了发生的事件的描述信息，比如消息值，屏幕坐标等，然后将它投递到相应的进程中，当该进程收到该消息时会查看该msg结构中的信息，也就知道了发生了什么事件，并对自已感兴趣的事件进行响应。

    下面我们就来用c++实现一个简单的监听者

[cpp] view plain copy print ?

1. #include <iostream>    
2. using namespace std;    
3. //listener基类(抽象类)    
4. class abstractlistener    
5. {    
6.     public:    
7.     abstractlistener(){};    
8.     virtual ~abstractlistener(){};    
9.     virtual void actionperformed(int state) = 0;    
10. };    
11. //listener实现类(它类似于操作系统中的进程)    
12. class statelistener:public abstractlistener    
13. {    
14.     public:    
15.     statelistener(){};    
16.     virtual ~statelistener(){};    
17.     virtual void actionperformed(int state);    
18. };    
19. void statelistener::actionperformed(int state)    
20. {            
21.     //这里就是对自已感兴趣的事件的相应处理    
22.     if(state==1){    
23.         cout<<"event 1 is fired."<<endl;    
24.     }else if(state==2){    
25.         cout<<"event 2 is fired."<<endl;    
26.     }else{    
27.         cout<<"other event is fired."<<endl;    
28.     }    
29. }    
30. //listener center(类似于操作系统(os))    
31. class listenercenter    
32. {    
33.     private:    
34.     statelistener listenerlist[50];//存储listener的数组    
35.     int count;//当前中心中已有的listener的个数    
36.     public:    
37.     listenercenter();    
38.     virtual ~listenercenter(){};    
39.     int getcount();    
40.     void addlistener(statelistener);    
41.     void firestatelistener(int state);    
42. };    
43. listenercenter::listenercenter()    
44. {    
45.     this->count=0;    
46. }    
47. int listenercenter::getcount()    
48. {    
49.     return count;    
50. }    
51. void listenercenter::addlistener(statelistener statelistener)    
52. {    
53.     listenerlist[this->count]=statelistener;    
54.     this->count++;    
55. }    
56. void listenercenter::firestatelistener(int state)    
57. {    
58.     for(int i=0;i<this->count;i++){    
59.         listenerlist[i].actionperformed(state);    
60.     }    
61. }    
62. int main(int argc, char* argv[])    
63. {    
64.     listenercenter listenercenter;    
65.     statelistener statelis1;    
66.     statelistener statelis2;    
67.     listenercenter.addlistener(statelis1);    
68.     listenercenter.addlistener(statelis2);    
69.     cout<<"=========================="<<endl;    
70.     listenercenter.firestatelistener(1);    
71.     cout<<"=========================="<<endl;    
72.     listenercenter.firestatelistener(2);    
73.     cout<<"=========================="<<endl;    
74.     listenercenter.firestatelistener(3);    
75.     cout<<"=========================="<<endl;    
76.     return 0;    
77. }   

#include <iostream>  
using namespace std;  
//listener基类(抽象类)  
class abstractlistener  
{  
	public:  
	abstractlistener(){};  
	virtual ~abstractlistener(){};  
	virtual void actionperformed(int state) = 0;  
};  
//listener实现类(它类似于操作系统中的进程)  
class statelistener:public abstractlistener  
{  
	public:  
	statelistener(){};  
	virtual ~statelistener(){};  
	virtual void actionperformed(int state);  
};  
void statelistener::actionperformed(int state)  
{          
	//这里就是对自已感兴趣的事件的相应处理  
	if(state==1){  
		cout<<"event 1 is fired."<<endl;  
	}else if(state==2){  
		cout<<"event 2 is fired."<<endl;  
	}else{  
		cout<<"other event is fired."<<endl;  
	}  
}  
//listener center(类似于操作系统(os))  
class listenercenter  
{  
	private:  
	statelistener listenerlist[50];//存储listener的数组  
	int count;//当前中心中已有的listener的个数  
	public:  
	listenercenter();  
	virtual ~listenercenter(){};  
	int getcount();  
	void addlistener(statelistener);  
	void firestatelistener(int state);  
};  
listenercenter::listenercenter()  
{  
	this->count=0;  
}  
int listenercenter::getcount()  
{  
	return count;  
}  
void listenercenter::addlistener(statelistener statelistener)  
{  
	listenerlist[this->count]=statelistener;  
	this->count++;  
}  
void listenercenter::firestatelistener(int state)  
{  
	for(int i=0;i<this->count;i++){  
		listenerlist[i].actionperformed(state);  
	}  
}  
int main(int argc, char* argv[])  
{  
	listenercenter listenercenter;  
	statelistener statelis1;  
	statelistener statelis2;  
	listenercenter.addlistener(statelis1);  
	listenercenter.addlistener(statelis2);  
	cout<<"=========================="<<endl;  
	listenercenter.firestatelistener(1);  
	cout<<"=========================="<<endl;  
	listenercenter.firestatelistener(2);  
	cout<<"=========================="<<endl;  
	listenercenter.firestatelistener(3);  
	cout<<"=========================="<<endl;  
	return 0;  
} 

打印：

==========================
event 1 is fired.
event 1 is fired.
==========================
event 2 is fired.
event 2 is fired.
==========================
other event is fired.
other event is fired.
==========================