C++ 之 代理模式

• 含义
• 模型图
• 示例代码
• 结构
• Demo
• • Subject
  • RealSubject
  • Proxy
  • main
  • 输出
• 参考

• 为其他对象提供一种代理以控制对这个对象的访问
  房客租房都需要通过中介，无法直接和房东进行沟通。

PS: 可恶的二房东某种程度上也算是中介，但是又不完全是中介。

模型图截图

#include 

class Subject {
 public:
  virtual void Request() const = 0;
};

class RealSubject : public Subject {
 public:
  void Request() const override {
    std::cout << "RealSubject: Handling request.n";
  }
};

class Proxy : public Subject {
  
 private:
  RealSubject *real_subject_;

  bool CheckAccess() const {
    // Some real checks should go here.
    std::cout << "Proxy: Checking access prior to firing a real request.n";
    return true;
  }
  void LogAccess() const {
    std::cout << "Proxy: Logging the time of request.n";
  }

  
 public:
  Proxy(RealSubject *real_subject) : real_subject_(new RealSubject(*real_subject)) {
  }

  ~Proxy() {
    delete real_subject_;
  }
  
  / *
  * 代理模式最常见的应用是延迟加载、缓存、控制访问、日志记录等。
  * 代理可以执行这些操作之一，然后根据结果将执行传递给链接的 RealSubject 对象中的相同方法 .
  */
  void Request() const override {
    if (this->CheckAccess()) {
      this->real_subject_->Request();
      this->LogAccess();
    }
  }
};

void ClientCode(const Subject &subject) {
  // ...
  subject.Request();
  // ...
}

int main() {
  std::cout << "Client: Executing the client code with a real subject:n";
  RealSubject *real_subject = new RealSubject;
  ClientCode(*real_subject);
  std::cout << "n";
  std::cout << "Client: Executing the same client code with a proxy:n";
  Proxy *proxy = new Proxy(real_subject);
  ClientCode(*proxy);

  delete real_subject;
  delete proxy;
  return 0;
}

• subject.h

#ifndef SUBJECT_H
#define SUBJECT_H


class Subject
{
public:
    Subject();
    virtual ~Subject();
    virtual void request() const = 0;
};

#endif // SUBJECT_H

• subject.cpp

#include "subject.h"

Subject::Subject()
{

}

Subject::~Subject()
{

}

• RealSubject.h

#ifndef REALSUBJECT_H
#define REALSUBJECT_H

#include "subject.h"
#include 
class RealSubject : public Subject
{
public:
    RealSubject();
    void request() const override
    {
        qDebug()<<"RealSubject: Handler requestn";
    }
};

#endif // REALSUBJECT_H

• RealSubject.cpp

#include "realsubject.h"

RealSubject::RealSubject()
{

}

void RealSubject::request() const
{
    qDebug()<<"RealSubject: Handler requestn";
}

• Proxy.h

#ifndef PROXY_H
#define PROXY_H

#include "subject.h"
#include "realsubject.h"

class Proxy : public Subject
{
public:
    Proxy();
    Proxy(RealSubject *realSub);
    ~Proxy();

    virtual void request() const override;

    bool CheckAccess() const;
    void LogAccess()  const;


private:
    RealSubject *m_realSubject;
};

#endif // PROXY_H

• Proxy.cpp

#include "proxy.h"

Proxy::Proxy()
{

}

Proxy::Proxy(RealSubject *realSub)
{
    m_realSubject = realSub;
}

Proxy::~Proxy()
{

}

void Proxy::request() const
{
    if(CheckAccess())
    {
        this->m_realSubject->request();
        this->LogAccess();
    }
}

bool Proxy::CheckAccess() const
{
    qDebug()<<"Proxy: Checking access prior to firing a real request.n";
    return true;
}

void Proxy::LogAccess() const
{
    qDebug()<<"Proxy: Record logn";
}

#include 

#include "subject.h"
#include "proxy.h"
#include "realsubject.h"

static void Client(Subject *subject)
{
    subject->request();
}


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    RealSubject *realSubject = new RealSubject();
    Client(realSubject);

    Proxy *proxy = new  Proxy(realSubject);
    Client(proxy);

    return a.exec();
}

RealSubject: Handler request

Proxy: Checking access prior to firing a real request.

RealSubject: Handler request

Proxy: Record log

1.在C++中使用代理模式
2.代理模式详解