C++代理模式

 

主要根据代理模式整理，感谢作者分享！

 [DP]上的定义：为其他对象提供一种代理以控制对这个对象的访问。有四种常用的情况：（1）远程代理，（2）虚代理，（3）保护代理，（4）智能引用。本文主要介绍虚代理和智能引用两种情况。

       考虑一个可以在文档中嵌入图形对象的文档编辑器。有些图形对象的创建开销很大。但是打开文档必须很迅速，因此我们在打开文档时应避免一次性创建所有开销很大的对象。这里就可以运用代理模式，在打开文档时，并不打开图形对象，而是打开图形对象的代理以替代真实的图形。待到真正需要打开图形时，仍由代理负责打开。这是[DP]一书上的给的例子。下面给出代理模式的UML图。

  1 #include <bits/stdc++.h>
  2 //#include "solution.h"
  3 using namespace std;
  4 
  5 #define debug(x) cout << #x << " at line " << __LINE__ << " is: " << x << endl
  6 
  7 class CImage
  8 {
  9 public:
 10     virtual ~CImage(){cout << "~CImage()\n";}
 11     virtual void Show(){}
 12 protected:
 13     CImage(string imgName): m_imgName(imgName){cout << "CImage()\n";}
 14     string m_imgName;
 15 };
 16 
 17 //concrete implement
 18 class CBigImage : public CImage
 19 {
 20 public:
 21     CBigImage(string imgName): CImage(imgName), m_bigImgName(imgName){
 22         cout << "CBigImage()\n";
 23     }
 24     ~CBigImage(){
 25         cout << "~CBigImage()\n";
 26     }
 27     void Show(){cout << "show big image" <<endl;}
 28 protected:
 29     string m_bigImgName;
 30 };
 31 
 32 // proxy
 33 class CBigImageProxy : public CImage
 34 {
 35 public:
 36     CBigImageProxy(string imgName): CImage(imgName), m_img(NULL), m_bigImgName(imgName){
 37         cout << "CBigImageProxy()\n";
 38     }
 39     ~CBigImageProxy(){
 40         if(NULL != m_img){
 41             delete m_img;
 42             m_img = NULL;
 43         }
 44         cout << "~CBigImageProxy()\n";
 45     }
 46     void Show(){
 47         if(NULL == m_img){
 48             m_img = new CBigImage(m_bigImgName);
 49         }
 50         m_img->Show();
 51     }
 52 private:
 53     CImage *m_img;
 54     string m_bigImgName;
 55 };
 56 
 57 
 58 class Subject
 59 {
 60 public:
 61     virtual ~Subject(){cout << "~Subject()\n";}
 62     virtual void Request()=0;
 63 protected:
 64     Subject(){cout << "Subject()\n";}
 65 };
 66 
 67 
 68 class ConcreteSubject : public Subject
 69 {
 70 public:
 71     ConcreteSubject(){
 72         cout << "ConcreteSubject()\n";
 73     }
 74     ~ConcreteSubject(){
 75         cout << "~ConcreteSubject()\n";
 76     }
 77     virtual void Request(){cout << "ConcreteSubject Request()\n";}
 78 };
 79 
 80 class Proxy : public Subject
 81 {
 82 public:
 83     Proxy(){
 84         cout << "Proxy()\n";
 85         this->m_sub = new ConcreteSubject();
 86     }
 87     //    Proxy(Subject* _sub):m_sub(_sub){
 88     //        cout << "Proxy(Subject)\n";
 89     //    }
 90 
 91     virtual void Request()//实现对委托者的委托任务执行与补偿
 92     {
 93         this->m_sub->Request();
 94     }
 95     ~Proxy(){
 96         if(NULL != this->m_sub){
 97             delete this->m_sub;
 98             this->m_sub = NULL;
 99         }
100         cout << "~Proxy()" << endl;
101     }
102 
103 private:
104     Subject *m_sub;
105 };
106 
107 
108 int main(int argc, char *argv[])
109 {
110     CBigImageProxy *bip = new CBigImageProxy("proxy.jpg");
111     bip->Show();
112     delete bip;
113     bip = NULL;
114 
115     Proxy *py = new Proxy();
116     py->Request();
117     delete py;
118     py = NULL;
119     return 0;
120 }
121 // g++ -g -Wall main.cpp -o xmain
两个代理模式的示例

 

至于智能指针，建议可以参考C++11标准的智能指针。

posted @ 2017-11-22 18:58  PKICA  阅读(533)  评论(0)  编辑  收藏  举报