设计模式 - FlyWeight 模式（享元模式）

作用：运用共享技术有效地支持大量细粒度的对象。 

 

UML结构图：

 

 

 

解析：

Flyweight模式在大量使用一些可以被共享的对象的时候经常使用.比如,在QQ聊天的时候很多时候你懒得回复又不得不回复的时候,一般会用一些客套的话语敷衍别人,如"呵呵","好的"等等之类的,这些简单的答复其实每个人都是提前定义好的,在使用的时候才调用出来.Flyweight就是基于解决这种问题的思路而产生的,当需要一个可以在其它地方共享使用的对象的时候,先去查询是否已经存在了同样的对象,如果没有就生成之有的话就直接使用.因此,Flyweight模式和Factory模式也经常混用。

实现：

需要说明的是下面的实现仅仅实现了对可共享对象的使用,非可共享对象的使用没有列出,因为这个不是Flyweight模式的重点.这里的实现要点是采用一个list链表来保存这些可以被共享的对象,需要使用的时候就到链表中查询是不是已经存在了,如果不存在就初始化一个,然后返回这个对象的指针。

 

代码实现： 

 1 
 2 #ifndef FLYWEIGHT_H
 3 #define FLYWEIGHT_H
 4 
 5 #include <string>
 6 #include <list>
 7 
 8 typedef std::string STATE;
 9 
10 class Flyweight
11 {
12 public:
13     virtual ~Flyweight(){}
14 
15     STATE GetIntrinsicState();
16     virtual void Operation(STATE& ExtrinsicState) = 0;
17 
18 protected:
19     Flyweight(const STATE& state) 
20         :m_State(state)
21     {
22     }
23 
24 private:
25     STATE m_State;
26 };
27 
28 class FlyweightFactory
29 {
30 public:
31     FlyweightFactory(){}
32     ~FlyweightFactory();
33 
34     Flyweight* GetFlyweight(const STATE& key);
35 
36 private:
37     std::list<Flyweight*>    m_listFlyweight;
38 };
39 
40 class ConcreateFlyweight
41     : public Flyweight
42 {
43 public:
44     ConcreateFlyweight(const STATE& state)
45         : Flyweight(state)
46     {
47     }
48     virtual ~ConcreateFlyweight(){}
49 
50     virtual void Operation(STATE& ExtrinsicState);
51 };
52 
53 #endif
54 

 

 

 1 #include "FlyWeight.h"
 2 #include <iostream>
 3 
 4 inline STATE Flyweight::GetIntrinsicState()
 5 {
 6     return m_State;
 7 }
 8 
 9 FlyweightFactory::~FlyweightFactory()
10 {
11     std::list<Flyweight*>::iterator iter1, iter2, temp;
12 
13     for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();
14         iter1 != iter2;
15         )
16     {
17         temp = iter1;
18         ++iter1;
19         delete (*temp);
20     }
21 
22     m_listFlyweight.clear();
23 }
24 
25 Flyweight* FlyweightFactory::GetFlyweight(const STATE& key)
26 {
27     std::list<Flyweight*>::iterator iter1, iter2;
28 
29     for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();
30          iter1 != iter2;
31          ++iter1)
32     {
33         if ((*iter1)->GetIntrinsicState() == key)
34         {
35             std::cout << "The Flyweight:" << key << " already exits"<< std::endl;
36             return (*iter1);
37         }
38     }
39 
40     std::cout << "Creating a new Flyweight:" << key << std::endl;
41     Flyweight* flyweight = new ConcreateFlyweight(key);
42     m_listFlyweight.push_back(flyweight);
43 }
44 
45 void ConcreateFlyweight::Operation(STATE& ExtrinsicState)
46 {
47 
48 }
49 

 

 

 1 #include "FlyWeight.h"
 2 
 3 int main()
 4 {
 5     FlyweightFactory flyweightfactory;
 6     flyweightfactory.GetFlyweight("hello");
 7     flyweightfactory.GetFlyweight("world");
 8     flyweightfactory.GetFlyweight("hello");
 9 
10     system("pause");
11     return 0;
12 }
13