《大话设计模式》读书笔记之C++实现--chapter24命令模式

#include <iostream>#include <QDebug>using namespace std;class ConcreteHandleSecond;class ConcreteHandleThird;//利用枚举类确定请求的等级enum Request{    Normal,    Important,    Urgent,    UrgentAndImport};//接口类定义处理请求的子类设置继承者以及具体的请求处理方法class Handle{public:    void SetSuccessor(Handle* successor)    {        m_successor = successor;    }    virtual void HandleRequest(Request type) = 0;    virtual ~Handle(){}                             //为避免内存泄漏，将基类的虚构函数定义为虚析构函数protected:    Handle* m_successor;};class ConcreteHandleFirst:public Handle{public:    void HandleRequest(Request type)    {        if(Normal == type)            cout << "ConcreteHandleFirst handle normal request" << endl;        else if(m_successor != nullptr && m_successor != Handle::m_successor)            m_successor->HandleRequest(type);        else                                        //如果继承者指针为空或者是基类的继承者指针，则无法处理请求            cout << "ConcreteHandleFirst no successor handle this request" << endl;    }};class ConcreteHandleSecond:public Handle{public:    void HandleRequest(Request type)    {        if(Important == type)            cout << "ConcreteHandleSecond handle important request" << endl;        else if(m_successor != nullptr && m_successor != Handle::m_successor)            m_successor->HandleRequest(type);        else            cout << "ConcreteHandleSecond no successor handle this request" << endl;    }};class ConcreteHandleThird:public Handle{public:    void HandleRequest(Request type)    {        if(Urgent == type)            cout << "ConcreteHandleThird handle urgent request" <<endl;        else if(m_successor != nullptr && m_successor != Handle::m_successor)        {            qDebug() << m_successor;            m_successor->HandleRequest(type);        }        else            cout << "ConcreteHandleThird no successor handle this request" << endl;    }};int main(int argc,char** argv){    Handle* handleFirst = new ConcreteHandleFirst();    Handle* handleSecond = new ConcreteHandleSecond();    Handle* handleThird = new ConcreteHandleThird();    handleFirst->SetSuccessor(handleSecond);    handleSecond->SetSuccessor(handleThird);    handleFirst->HandleRequest(Urgent);    return 0;}