深入浅出设计模式原则之单一原则（SRP)

﹏ヽ暗。殇╰゛Y 2023-01-03 15:28 161阅读 0赞

## ![91a73976b13d9d42ba5fe5d0b9bb065e.png][] ##

**下面以两个例子来解释一下单一原则（[工程源代码][Link 1]）**

**【案例1】用户权限系统**

设计案例用户权限系统（用户、机构、角色管理这些模块），基本上使用的都是RBAC模型（基于角色的访问控制，通过分配和取消角色来完成用户权限的授予和取消，使动作主体（用户）与资源的行为（权限）分离），确实是一个很好的解决方案。

**传统方法：**

#include <QCoreApplication>
    #include <iostream>
    /*!
     * \brief The UserInfo class
     */
    class UserInfo
     {
     public:
    
         void SetUserID(std::string userID);
         std::string GetUserID();
         void SetUserName(std::string userName);
         std::string GetUserName();
         void SetUserPasswd(std::string userPasswd);
         std::string GetUserPasswd();
    
         void DeleteUser(std::string userName);
         void ChangeUserPasswd(std::string &oldUserPasswd,std::string &newUserPasswd);
         void AddOrg(int orgID);
         void AddRole(int roleID);
    
     private:
         std::string _user_id;
         std::string _user_name;
         std::string _user_passwd;
    
     };
    
    /*!
     * \brief UserInfo::SetUserID
     * \param userID
     */
    void UserInfo::SetUserID(std::string userID)
    {
        this->_user_id = userID;
    }
    /*!
     * \brief UserInfo::GetUserID
     * \return
     */
    std::string UserInfo::GetUserID()
    {
        std::cout<<this->_user_id.c_str()<<std::endl;
        return this->_user_id;
    }
    /*!
     * \brief UserInfo::SetUserName
     * \param userName
     */
    void UserInfo::SetUserName(std::string userName)
    {
        this->_user_name = userName;
    }
    /*!
     * \brief UserInfo::GetUserName
     * \return
     */
    std::string UserInfo::GetUserName()
    {
        std::cout<<this->_user_name.c_str()<<std::endl;
        return this->_user_name;
    }
    /*!
     * \brief UserInfo::SetUserPasswd
     * \param userPasswd
     */
    void UserInfo::SetUserPasswd(std::string userPasswd)
    {
        this->_user_passwd = userPasswd;
    }
    /*!
     * \brief UserInfo::GetUserPasswd
     * \return
     */
    std::string UserInfo::GetUserPasswd()
    {
        std::cout<<this->_user_passwd.c_str()<<std::endl;
        return this->_user_passwd;
    }
    /*!
     * \brief UserInfo::DeleteUser
     * \param userName
     */
    void UserInfo::DeleteUser(std::string userName)
    {
    
    }
    /*!
     * \brief UserInfo::ChangeUserPasswd
     * \param oldUserPasswd
     * \param newUserPasswd
     */
    void UserInfo::ChangeUserPasswd(std::string &oldUserPasswd, std::string &newUserPasswd)
    {
    
    }
    /*!
     * \brief UserInfo::AddOrg
     * \param orgID
     */
    void UserInfo::AddOrg(int orgID)
    {
    
    }
    /*!
     * \brief UserInfo::AddRole
     * \param roleID
     */
    void UserInfo::AddRole(int roleID)
    {
    
    }
    
    
    int main(int argc, char *argv[])
    {
        QCoreApplication a(argc, argv);
        UserInfo *myUserInfo = new UserInfo;
        myUserInfo->SetUserName("lili");
        myUserInfo->SetUserID("C-1");
        myUserInfo->SetUserPasswd("123456");
        myUserInfo->GetUserName();
        myUserInfo->GetUserID();
        myUserInfo->GetUserPasswd();
        delete myUserInfo;
        return a.exec();
    }

以上设计不符合单一原则，解决方法如下：

依据定义咱们可以再重新设计下，把用户的信息抽取成一个业务对象（Business Object ，BO）,把行为抽取成一个业务逻辑（Business Logic，Biz）

#include <QCoreApplication>
    #include <iostream>
    /*!
     * \brief The UserBo class
     */
    class UserBo
     {
     public:
         void SetUserID(std::string userID);
         std::string GetUserID();
         void SetUserName(std::string userName);
         std::string GetUserName();
         void SetUserPasswd(std::string userPasswd);
         std::string GetUserPasswd();
    
     public:
         std::string _user_id;
         std::string _user_name;
         std::string _user_passwd;
     };
    /*!
     * \brief UserBo::SetUserID
     * \param userID
     */
    void UserBo::SetUserID(std::string userID)
    {
        this->_user_id = userID;
    }
    /*!
     * \brief UserBo::GetUserID
     * \return
     */
    std::string UserBo::GetUserID()
    {
        std::cout<<this->_user_id.c_str()<<std::endl;
        return this->_user_id;
    }
    /*!
     * \brief UserBo::SetUserName
     * \param userName
     */
    void UserBo::SetUserName(std::string userName)
    {
        this->_user_name = userName;
    }
    /*!
     * \brief UserBo::GetUserName
     * \return
     */
    std::string UserBo::GetUserName()
    {
        std::cout<<this->_user_name.c_str()<<std::endl;
        return this->_user_name;
    }
    /*!
     * \brief UserBo::SetUserPasswd
     * \param userPasswd
     */
    void UserBo::SetUserPasswd(std::string userPasswd)
    {
          this->_user_passwd = userPasswd;
    }
    /*!
     * \brief UserBo::GetUserPasswd
     * \return
     */
    std::string UserBo::GetUserPasswd()
    {
        std::cout<<this->_user_passwd.c_str()<<std::endl;
        return this->_user_passwd;
    }
    /*!
     * \brief The UserBiz class
     */
    class UserBiz
     {
     public:
         void DeleteUser(UserBo myUserBo);
         void ChangeUserPasswd(UserBo *myUserBo,std::string &oldUserPasswd,std::string &newUserPasswd);
         void AddOrg(UserBo myUserBo,int orgID);
         void AddRole(UserBo myUserBo,int roleID);
     };
    
    /*!
     * \brief UserBiz::DeleteUser
     * \param myUserBo
     */
    void UserBiz::DeleteUser(UserBo myUserBo)
    {
    
    }
    /*!
     * \brief UserBiz::ChangeUserPasswd
     * \param oldUserPasswd
     * \param newUserPasswd
     */
    void UserBiz::ChangeUserPasswd(UserBo *myUserBo,std::string &oldUserPasswd, std::string &newUserPasswd)
    {
       if (!myUserBo->_user_passwd.compare(oldUserPasswd)){
           myUserBo->_user_passwd = newUserPasswd;
           std::cout<<myUserBo->_user_passwd<<std::endl;
       }
    
    }
    /*!
     * \brief UserBiz::AddOrg
     * \param myUserBo
     * \param orgID
     */
    void UserBiz::AddOrg(UserBo myUserBo, int orgID)
    {
    
    }
    /*!
     * \brief UserBiz::AddRole
     * \param myUserBo
     * \param roleID
     */
    void UserBiz::AddRole(UserBo myUserBo, int roleID)
    {
    
    }
    /*!
     * \brief The NewUserInfo class
     */
    class UserInfo : public UserBo,public UserBiz
     {
    
     };
    
    
    int main(int argc, char *argv[])
    {
        QCoreApplication a(argc, argv);
    
        UserInfo *myUserInfo = new UserInfo;
    
        UserBo *myUserBo= (UserBo *)myUserInfo;
        myUserBo->SetUserName("lili");
        myUserBo->SetUserID("C-1");
        myUserBo->SetUserPasswd("123456");
        myUserBo->GetUserID();
        myUserBo->GetUserName();
        myUserBo->GetUserPasswd();
    
        UserBiz *myUserBiz = (UserBiz *)myUserInfo;
        myUserBiz->ChangeUserPasswd(myUserBo,myUserBo->_user_passwd,std::string("789012"));
        return a.exec();
    }

**单一职责原则规定一个类应该有且仅有一个引起它变化的原因，否则类应该被拆分。**

**在实际应用中，类的设计尽量做到只有一个原因引起变化，接口一定要做到单一职责原则，方法一定要做到单一职责原则，即一个方法只实现一个功能。**

参考文献：

1.  [单一职责原则（Single Responsibility Principle）][Single Responsibility Principle]
2.  [单一职责原则——面向对象设计原则][Link 2]
3.  [设计模式七大原则][Link 3]
4.  [单一职责原则（C++)][C]
5.  [单一职责原则][Link 4]
6.  [C++ string字符串比较方法详解][C_ string]

[91a73976b13d9d42ba5fe5d0b9bb065e.png]: /images/20221119/7a279f9a94bf4b1286c069235545349d.png
[Link 1]: https://download.csdn.net/download/a8039974/14094665
[Single Responsibility Principle]: https://www.cnblogs.com/gaochundong/p/single_responsibility_principle.html
[Link 2]: http://c.biancheng.net/view/1327.html
[Link 3]: https://www.cnblogs.com/zhaye/p/11176906.html
[C]: https://www.kanzhun.com/jiaocheng/394169.html
[Link 4]: https://www.jianshu.com/p/09c147a19631
[C_ string]: http://c.biancheng.net/view/1447.html