c++设计模式

简介

以下面代码为例

一、分解

Shape.h

class Point{
public:
	int x;
	int y;
};

class Line{
public:
	Point start;
    Point end;

	Line(const Point& start, const Point& end){
        this->start = start;
        this->end = end;
    }

};

class Rect{
public:
	Point leftUp;
    int width;
	int height;

	Rect(const Point& leftUp, int width, int height){
        this->leftUp = leftUp;
        this->width = width;
		this->height = height;
    }

};

//增加
class Circle{
public:
    point center;//圆心
    int r;//半径
    
    Circle(const Point& c, int r){
		this->center = c;
		this->r = r;
		
	}
  

};

MainForm.cpp

//这里写的伪代码 继承的Form不管他
class MainForm : public Form {
private:
	Point p1;
	Point p2;

    //改变
	vector lineVector;
	vector rectVector;
	//增加圆
	vector circleVector;

public:
	MainForm(){
		//...
	}
protected:

	virtual void onMouseDown(const MouseEventArgs& e);
	virtual void onMouseUp(const MouseEventArgs& e);
	virtual void onPaint(const PaintEventArgs& e);
};


void MainForm::onMouseDown(const MouseEventArgs& e){
	p1.x = e.X;
	p1.y = e.Y;

	//...
	Form::onMouseDown(e);
}

void MainForm::onMouseUp(const MouseEventArgs& e){
	p2.x = e.X;
	p2.y = e.Y;

	if (rdoLine.Checked){
		Line line(p1, p2);
		lineVector.push_back(line);
	}
	else if (rdoRect.Checked){
		int width = abs(p2.x - p1.x);
		int height = abs(p2.y - p1.y);
		Rect rect(p1, width, height);
		rectVector.push_back(rect);
	}
	//增加
	else if (rdoCircle.Checked){
    	Point center=p1;
        int r=sqrt((p2.x-p1.x)*(p2.x-p1.x) + (p2.y-p1.y)*(p2.y-p1.y)); 
        Circle circle(center,r);
		circleVector.push_back(circle);
	}

	//...
	this->Refresh();

	Form::onMouseUp(e);
}

void MainForm::onPaint(const PaintEventArgs& e){

	//画线
	for (int i = 0; i < lineVector.size(); i++){
		e.Graphics.DrawLine(Pens.Red,
			lineVector[i].start.x, 
			lineVector[i].start.y,
			lineVector[i].end.x,
			lineVector[i].end.y);
	}

	//画矩阵
	for (int i = 0; i < rectVector.size(); i++){
		e.Graphics.DrawRectangle(Pens.Red,
			rectVector[i].leftUp,
			rectVector[i].width,
			rectVector[i].height);
	}

	//憎加
	//画圆
	for (int i = 0; i < circleVector.size(); i++){
		e.Graphics.DrawCircle(Pens.Red,
			circleVector[i].center,
                circleVector[i].r );
	}

	//...
	Form::onPaint(e);
}

二、抽象

Shape.h

采用多态机制

class Shape{
public:
	virtual void Draw(const Graphics& g)=0;
	virtual ~Shape() { }
};


class Point{
public:
	int x;
	int y;
};

class Line: public Shape{
public:
	Point start;
	Point end;

	Line(const Point& start, const Point& end){
		this->start = start;
		this->end = end;
	}

	//实现自己的Draw，负责画自己
	virtual void Draw(const Graphics& g){
		g.DrawLine(Pens.Red, 
			start.x, start.y,end.x, end.y);
	}

};

class Rect: public Shape{
public:
	Point leftUp;
	int width;
	int height;

	Rect(const Point& leftUp, int width, int height){
		this->leftUp = leftUp;
		this->width = width;
		this->height = height;
	}

	//实现自己的Draw，负责画自己
	virtual void Draw(const Graphics& g){
		g.DrawRectangle(Pens.Red,
			leftUp,width,height);
	}

};

//增加圆的数据结构
class Circle : public Shape{
public:
    point center;//圆心
    int r;//半径
    
    Circle(const Point& c, int r){
		this->center = c;
		this->r = r;
		
	}
  
	//实现自己的Draw，负责画自己
	virtual void Draw(const Graphics& g){
		g.DrawCircle(Pens.Red,
			center,r);
	}

};

MainForm.cpp

class MainForm : public Form {
private:
	Point p1;
	Point p2;

	//针对所有形状 统一处理
	vector shapeVector;// shape*指针 是因为动态的机制

public:
	MainForm(){
		//...
	}
protected:

	virtual void onMouseDown(const MouseEventArgs& e);
	virtual void onMouseUp(const MouseEventArgs& e);
	virtual void onPaint(const PaintEventArgs& e);
};


void MainForm::onMouseDown(const MouseEventArgs& e){
	p1.x = e.X;
	p1.y = e.Y;

	//...
	Form::onMouseDown(e);
}

void MainForm::onMouseUp(const MouseEventArgs& e){
	p2.x = e.X;
	p2.y = e.Y;

	if (rdoLine.Checked){
		shapeVector.push_back(new Line(p1,p2));// new 一个堆指针
	}
	else if (rdoRect.Checked){
		int width = abs(p2.x - p1.x);
		int height = abs(p2.y - p1.y);
		shapeVector.push_back(new Rect(p1, width, height));
	}
	//增加
	else if (...){
		Point center=p1;
        int r=sqrt((p2.x-p1.x)*(p2.x-p1.x) + (p2.y-p1.y)*(p2.y-p1.y)); 
        Circle circle(center,r);
		shapeVector.push_back(circle);
	}

	//...
	this->Refresh();

	Form::onMouseUp(e);
}

void MainForm::onPaint(const PaintEventArgs& e){


	for (int i = 0; i < shapeVector.size(); i++){

		shapeVector[i]->Draw(e.Graphics); //多态调用，各负其责 是line就调用line的Draw  是Rect就调用Rect 的Draw
	}

	//...
	Form::onPaint(e);
}

面向对象设计原则

这个其实就是扩展

一个类不能乱指向

子类继承父类，那肯定是有原因的

不要把不必要的方法public出去，如果只是子类用就protected ,如果是本类用就private

对象组合比如就是 class a里面放一个 class b

继承子类父类耦合度过高就是父类给子类暴露了太多东西

封装变化点一侧变化一侧稳定

这里放的就是具体类型，违背面向对象原则

而这个则就是给了一个抽象接口，符合原则。

其实软件的设计也是借鉴其他行业的原则！！！

模板方法Template Method

早绑定

这里的方法没有采用template_method

template_lib.cpp

//程序库开发人员
class Library{

public:
	void Step1(){
		//...
	}

    void Step3(){
		//...
    }

    void Step5(){
		//...
    }
};

template_app.cpp

//应用程序开发人员
class Application{
public:
	bool Step2(){
		//...
    }

    void Step4(){
		//...
    }
};

int main()
{
	//模拟程序流程
	Library lib();
	Application app();

	lib.Step1();

	if (app.Step2()){
		lib.Step3();
	}

	for (int i = 0; i < 4; i++){
		app.Step4();
	}

	lib.Step5();

}

一个晚的东西调用早的东西就是早绑定

晚绑定

采用 template method 的设计模式—前提是你要有稳定的骨架

程序主流程相对稳定

template_lib.cpp

//程序库开发人员
class Library{
public:
	//稳定 template method
    void Run(){
        
        Step1();

        if (Step2()) { //支持变化 ==> 虚函数的多态调用
            Step3(); 
        }

        for (int i = 0; i < 4; i++){
            Step4(); //支持变化 ==> 虚函数的多态调用
        }

        Step5();

    }
	virtual ~Library(){ }//基类的析构写成虚的  因为如果你 new一个子类出来 你要delete子类的话 如果基类的虚构没有写成虚的，可能子类不一定能调用到自己的析构

protected:
	
	void Step1() { //稳定
        //.....
    }
	void Step3() {//稳定
        //.....
    }
	void Step5() { //稳定
		//.....
	}
    //虚函数支持变化
	virtual bool Step2() = 0;//变化 
    virtual void Step4() =0; //变化
};

template_app.cpp

//应用程序开发人员
//继承库 来进行开发
class Application : public Library {
protected:
	virtual bool Step2(){
		//... 子类重写实现
    }

    virtual void Step4() {
		//... 子类重写实现
    }
};

int main()
	{
	//多态指针
	    Library* pLib=new Application();
	    lib->Run();//这里依然会根据流程来走

		delete pLib;//
	}
}

早的东西调用晚的东西就是晚绑定

红色的代表稳定

蓝色的代表不稳定

策略模式违背开闭原则

enum Taxbase {
	CN_Tax,
	US_Tax,
	DE_Tax,
	FR_Tax       //更改 违背开闭原则
};

class SalesOrder{
    Taxbase tax;
public:
    double CalculateTax(){
        //...
        
        if (tax == CN_Tax){
            //CN***********
        }
        else if (tax == US_Tax){
            //US***********
        }
        else if (tax == DE_Tax){
            //DE***********
        }
		else if (tax == FR_Tax){  //更改
			//...
		}

        //....
     }
    
};

这里要改动的东西多，同时if else 也消耗性能

符合开闭原则

策略模式

class TaxStrategy{
public:
    virtual double Calculate(const Context& context)=0;
    virtual ~TaxStrategy(){}
};


class CNTax : public TaxStrategy{
public:
    virtual double Calculate(const Context& context){
        /

class House{
    //....
};

class HouseBuilder {
public:
    House* GetResult(){//获得house指针

        return pHouse;
    }
    virtual ~HouseBuilder(){}
protected:
    
    House* pHouse;
	virtual void BuildPart1()=0;
    virtual void BuildPart2()=0;
    virtual void BuildPart3()=0;
    virtual void BuildPart4()=0;
    virtual void BuildPart5()=0;
	
};

class StoneHouse: public House{
    
};

class StoneHouseBuilder: public HouseBuilder{
protected:
    
    virtual void BuildPart1(){
        //pHouse->Part1 = ...;//这里面用到house里面的东西
    }
    virtual void BuildPart2(){
        
    }
    virtual void BuildPart3(){
        
    }
    virtual void BuildPart4(){
        
    }
    virtual void BuildPart5(){
        
    }
    
};


class HouseDirector{
    
public:
    HouseBuilder* pHouseBuilder;
    
    HouseDirector(HouseBuilder* pHouseBuilder){
        this->pHouseBuilder=pHouseBuilder;
    }
    
    House* Construct(){
        
        pHouseBuilder->BuildPart1();
        
        for (int i = 0; i < 4; i++){
            pHouseBuilder->BuildPart2();
        }
        
        bool flag=pHouseBuilder->BuildPart3();
        
        if(flag){
            pHouseBuilder->BuildPart4();
        }
        
        pHouseBuilder->BuildPart5();
        
        return pHouseBuilder->GetResult();
    }
};

红色的代表稳定，蓝色的代表变化

这里面就是指

HouseBuilder HouseDirector稳定

StoneHouseBuilder等具体的子类是变化的

单件模式


class Singleton{
private://这样写就是外部无法使用默认构造
    Singleton();
    Singleton(const Singleton& other);
public:
    static Singleton* getInstance();
    static Singleton* m_instance;
};

Singleton* Singleton::m_instance=nullptr;

//线程非安全版本
Singleton* Singleton::getInstance() {
    if (m_instance == nullptr) {
        m_instance = new Singleton();
    }
    return m_instance;//保证唯一

}






//线程安全版本，但锁的代价过高---因为对于都是读操作的线程是浪费的。
//就是只有35行执行结束了，才会释放锁，其他线程才能到32行 这时候m_instance已经不是空了
Singleton* Singleton::getInstance() {
    Lock lock;
    if (m_instance == nullptr) {
        m_instance = new Singleton();
    }
    return m_instance;
}









//双检查锁，但由于内存读写reorder不安全
Singleton* Singleton::getInstance() {
    
    if(m_instance==nullptr){//锁前检查避免读操作代价过高的问题
        Lock lock;
        if (m_instance == nullptr) {//双检查 
            m_instance = new Singleton();//默认的顺序：先分配内存 再调用构造器，再把地址赋值给m_instance  
                                        //reorder之后顺序有可能为：先分配内存 ，把地址赋值给m_instance，再调用构造器  这样就导致读存在问题 因为只是分配了原生的内存，没有执行构造器
        }
    }
    return m_instance;
}








//C++ 11版本之后的跨平台实现 (volatile)
std::atomic Singleton::m_instance;//原子对象
std::mutex Singleton::m_mutex;

Singleton* Singleton::getInstance() {
    Singleton* tmp = m_instance.load(std::memory_order_relaxed);//tmp这个指针乐意屏蔽编译器的reorder
    std::atomic_thread_fence(std::memory_order_acquire);//内存fence (内存的屏障 内存reorder的保护)
    //下面的tmp就不会被reorder了
    if (tmp == nullptr) {
        std::lock_guard lock(m_mutex);//上锁
        tmp = m_instance.load(std::memory_order_relaxed);//1内存
        if (tmp == nullptr) {//
            tmp = new Singleton;//2 构造 不会被reorder一定是先执行它 再执行构造器，再把值返回
            std::atomic_thread_fence(std::memory_order_release);//释放内存fence
            m_instance.store(tmp, std::memory_order_relaxed);//3返回到m_instance
        }
    }
    return tmp;
}

享元模式

class Font {
private:

    //unique object key
    string key;
    
    //object state
    //....
    
public:
    Font(const string& key){
        //...
    }
};
ß

class FontFactory{//共享 把要用的对象放在一个共享池里
private:
    map fontPool;
    
public:
    Font* GetFont(const string& key){

        map::iterator item=fontPool.find(key);
        
        if(item!=footPool.end()){
            return fontPool[key];
        }
        else{
            Font* font = new Font(key);
            fontPool[key]= font;
            return font;
        }

    }
    
    void clear(){
        //...
    }

};

门面模式

以数据库为例

红色的部分是稳定的，比如返回数据库对象啊什么的

蓝色部分改变的，比如数据表结构，数据连接方式

代理模式

client.cpp

没有使用代理模式

class ISubject{
public:
    virtual void process();
};


class RealSubject: public ISubject{
public:
    virtual void process(){
        //....
    }
};

class ClientApp{
    
    ISubject* subject;
    
public:
    
    ClientApp(){
        subject=new RealSubject();
    }
    
    void DoTask(){
        //...
        subject->process();
        
        //....
    }
};

proxy.cpp

使用了代理模式

class ISubject{
public:
    virtual void process();
};


//Proxy的设计
class SubjectProxy: public ISubject{
    
    
public:
    virtual void process(){
        //对RealSubject的一种间接访问  就是这里和上面的client.cpp有区别 这里面实际上会比上面的复杂很多 ，用SubjectProxy类进行隔离。
        //....
    }
};

class ClientApp{
    
    ISubject* subject;
    
public:
    
    ClientApp(){
        subject=new SubjectProxy();
    }
    
    void DoTask(){
        //...
        subject->process();
        
        //....
    }
};

适配器

老的东西放在新的里面使用

//目标接口（新接口）
class ITarget{
public:
    virtual void process()=0;
};

//遗留接口（老接口）
class IAdaptee{
public:
    virtual void foo(int data)=0;
    virtual int bar()=0;
};

//遗留类型
class OldClass: public IAdaptee{
    //.... 重写IAdaptee里面的方法等操作
};

//对象适配器
class Adapter: public ITarget{ //继承
protected:
    IAdaptee* pAdaptee;//组合
    
public:
    
    Adapter(IAdaptee* pAdaptee){
        this->pAdaptee=pAdaptee;
    }
    
    virtual void process(){
        int data=pAdaptee->bar();
        pAdaptee->foo(data);
        
    }
    
    
};


//类适配器 没有灵活性 
class Adapter: public ITarget,
               protected OldClass{ //多继承  // protected 和private继承可以叫做实现继承 就是我没有继承你的接口，但是我用你的实现
               
               
}


int main(){
    IAdaptee* pAdaptee=new OldClass();//旧类对象
    
    
    ITarget* pTarget=new Adapter(pAdaptee);//旧类对象塞进adpater里面产生新类对象
    pTarget->process();
    
    
}

//这些也是用到了adapter
class stack{
    deqeue container;
    
};

class queue{
    deqeue container;
    
};

中介者模式

状态模式

没有使用状态模式

cenum NetworkState
{
    Network_Open,
    Network_Close,
    Network_Connect,
};

class NetworkProcessor{
    
    NetworkState state;

public:
    
    void Operation1(){
        if (state == Network_Open){

            //**********
            state = Network_Close;
        }
        else if (state == Network_Close){

            //..........
            state = Network_Connect;
        }
        else if (state == Network_Connect){

            //$$$$$$$$$$
            state = Network_Open;
        }
    }

    public void Operation2(){

        if (state == Network_Open){
            
            //**********
            state = Network_Connect;
        }
        else if (state == Network_Close){

            //.....
            state = Network_Open;
        }
        else if (state == Network_Connect){

            //$$$$$$$$$$
            state = Network_Close;
        }
    
    }

    public void Operation3(){

    }
};

上面的代码采用了很多if else

使用状态模式

class NetworkState{

public:
    NetworkState* pNext;//指向状态改变后的状态
    virtual void Operation1()=0;
    virtual void Operation2()=0;
    virtual void Operation3()=0;

    virtual ~NetworkState(){}
};

//我们把各个不同state的operation都分别在不同的state类里面实现 这样程序的框架更加明显 也更方便后期代码的添加和修改

class OpenState :public NetworkState{
    
    static NetworkState* m_instance;
public:
    static NetworkState* getInstance(){
        if (m_instance == nullptr) {
            m_instance = new OpenState();
        }
        return m_instance;
    }

    void Operation1(){
        
        //**********
        pNext = CloseState::getInstance();
    }
    
    void Operation2(){
        
        //..........
        pNext = ConnectState::getInstance();
    }
    
    void Operation3(){
        
        //$$$$$$$$$$
        pNext = OpenState::getInstance();
    }
};

class CloseState :public NetworkState{
    
    static NetworkState* m_instance;
public:
    static NetworkState* getInstance(){
        if (m_instance == nullptr) {
            m_instance = new CloseState();
        }
        return m_instance;
    }

    void Operation1(){
        
        //**********
        pNext = ConnectState::getInstance();
    }
    
    void Operation2(){
        
        //..........
         pNext = OpenState::getInstance();
    }
    
    void Operation3(){
        
        //$$$$$$$$$$
        
    }
};


//
class NetworkProcessor
{
    NetworkState* pState;
  public:
    NetworkProcessor(NetworkState* pState)
    {
        this->pState=pState;
    }
    
    void Operation1()
    {
        //...
        pState->Operation1();
        pState=pState->pNext;
        //...
	}
    void Operation2(){
        //...
        pState->Operation2();
        pState = pState->pNext;
        //...
    }
    
    void Operation3(){
        //...
        pState->Operation3();
        pState = pState->pNext;
        //...
    }
    
    
    
};

红色的是稳定的

蓝色的是变化的

备忘录Memento

class Memento//备忘录
{
    string state;
    //..
public:
    Memento(const string & s) : state(s) {}
    string getState() const { return state; }
    void setState(const string & s) { state = s; }
};



class Originator
{
    string state;
    //....
public:
    Originator() {}
    Memento createMomento() {
        Memento m(state);
        return m;
    }
    void setMomento(const Memento & m) {
        state = m.getState();
    }
};



int main()
{
    Originator orginator;
    
    //捕获对象状态，存储到备忘录
    Memento mem = orginator.createMomento();//类似于深拷贝 把原来的状态拷贝到新的对象里
    
    //... 改变orginator状态
    
    //从备忘录中恢复
    orginator.setMomento(mem);

   
    
}

组合模式

#include 
#include 
#include 
#include 

using namespace std;

class Component 
{
public:
    virtual void process() = 0;//统一接口
    virtual ~Component(){}
};

//树节点
class Composite : public Component{
    
    string name;
    list elements; //这里list里面有可能是 Composite 也有可能是 Leaf
public:
    Composite(const string & s) : name(s) {}
    
    void add(Component* element) {
        elements.push_back(element);
    }
    void remove(Component* element){
        elements.remove(element);
    }
    
    void process(){
        
        //1. process current node
        
        
        //2. process leaf nodes
        for (auto &e : elements)
            e->process(); //多态调用
         
    }
};

//叶子节点
class Leaf : public Component{
    string name;
public:
    Leaf(string s) : name(s) {}
            
    void process(){
        //process current node
    }
};

//客户程序
void Invoke(Component & c){
    //...
    c.process();
    //...
}


int main()
{

    Composite root("root");
    Composite treeNode1("treeNode1");
    Composite treeNode2("treeNode2");
    Composite treeNode3("treeNode3");
    Composite treeNode4("treeNode4");
    Leaf leat1("left1");
    Leaf leat2("left2");
    
    root.add(&treeNode1);
    treeNode1.add(&treeNode2);
    treeNode2.add(&leaf1);
    
    root.add(&treeNode3);
    treeNode3.add(&treeNode4);
    treeNode4.add(&leaf2);
    
    process(root);
    process(leaf2);
    process(treeNode3);
  
}

迭代器

现在在c++里面来看这个模式已经是落伍了因为它是基于虚函数面向对象的迭代器相比于stl 泛型编程基于模板的多态迭代器效率要低。

template
class Iterator
{
public:
    virtual void first() = 0;
    virtual void next() = 0;
    virtual bool isDone() const = 0;
    virtual T& current() = 0;
};



template
class MyCollection{
    
public:
    
    Iterator GetIterator(){
        //...
    }
    
};

template
class CollectionIterator : public Iterator{
    MyCollection mc;
public:
    
    CollectionIterator(const MyCollection & c): mc(c){ }
    
    void first() override {
        
    }
    void next() override {
        
    }
    bool isDone() const override{
        
    }
    T& current() override{
        
    }
};

void MyAlgorithm()
{
    MyCollection mc;
    
    Iterator iter= mc.GetIterator();
    
    for (iter.first(); !iter.isDone(); iter.next()){//虚函数是运行时多态 效率低于编译时多态（编译时已经把工作做了 就不需要运行的时候再计算函数地址了）
        cout << iter.current() << endl;
    }
    
}

职责链

#include 
#include 

using namespace std;

enum class RequestType
{
    REQ_HANDLER1,
    REQ_HANDLER2,
    REQ_HANDLER3
};

//  请求类
class Reqest
{
    string description;
    RequestType reqType;
public:
    Reqest(const string & desc, RequestType type) : description(desc), reqType(type) {}
    RequestType getReqType() const { return reqType; }
    const string& getDescription() const { return description; }
};

//职责链
class ChainHandler{
    
    ChainHandler *nextChain;//多态指针指向自身 形成链表  这样j
    void sendReqestTonextHandler(const Reqest & req)
    {
        if (nextChain != nullptr)
            nextChain->handle(req);
    }
protected:
    virtual bool canHandleRequest(const Reqest & req) = 0;//判断能不能处理这个请求
    virtual void processRequest(const Reqest & req) = 0;//具体处理请求
public:
    ChainHandler() { nextChain = nullptr; }//初始化
    void setNextChain(ChainHandler *next) { nextChain = next; }
    
   
    void handle(const Reqest & req)
    {
        if (canHandleRequest(req))
            processRequest(req);
        else
            sendReqestTonextHandler(req);//跳到下一个要处理
    }
};


//职责链中具体要处理的类
class Handler1 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER1;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler1 is handle reqest: " << req.getDescription() << endl;
    }
};
        
class Handler2 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER2;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler2 is handle reqest: " << req.getDescription() << endl;
    }
};

class Handler3 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER3;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler3 is handle reqest: " << req.getDescription() << endl;
    }
};

int main(){
    Handler1 h1;
    Handler2 h2;
    Handler3 h3;
    h1.setNextChain(&h2);
    h2.setNextChain(&h3);
    
    Reqest req("process task ... ", RequestType::REQ_HANDLER3);
    h1.handle(req);
    return 0;
}

void next() override {

}
bool isDone() const override{
    
}
T& current() override{
    
}

};

void MyAlgorithm()
{
MyCollection mc;

Iterator iter= mc.GetIterator();

for (iter.first(); !iter.isDone(); iter.next()){//虚函数是运行时多态 效率低于编译时多态（编译时已经把工作做了 就不需要运行的时候再计算函数地址了）
    cout << iter.current() << endl;
}

}



[外链图片转存中...(img-fyKsXrfx-1633924054004)]

[外链图片转存中...(img-CEbxcAeZ-1633924054004)]

[外链图片转存中...(img-z2eQhKpq-1633924054004)]

# 职责链

[外链图片转存中...(img-MLPjq5ZX-1633924054005)]

[外链图片转存中...(img-CC0IPwVj-1633924054005)]

~~~c++
#include 
#include 

using namespace std;

enum class RequestType
{
    REQ_HANDLER1,
    REQ_HANDLER2,
    REQ_HANDLER3
};

//  请求类
class Reqest
{
    string description;
    RequestType reqType;
public:
    Reqest(const string & desc, RequestType type) : description(desc), reqType(type) {}
    RequestType getReqType() const { return reqType; }
    const string& getDescription() const { return description; }
};

//职责链
class ChainHandler{
    
    ChainHandler *nextChain;//多态指针指向自身 形成链表  这样j
    void sendReqestTonextHandler(const Reqest & req)
    {
        if (nextChain != nullptr)
            nextChain->handle(req);
    }
protected:
    virtual bool canHandleRequest(const Reqest & req) = 0;//判断能不能处理这个请求
    virtual void processRequest(const Reqest & req) = 0;//具体处理请求
public:
    ChainHandler() { nextChain = nullptr; }//初始化
    void setNextChain(ChainHandler *next) { nextChain = next; }
    
   
    void handle(const Reqest & req)
    {
        if (canHandleRequest(req))
            processRequest(req);
        else
            sendReqestTonextHandler(req);//跳到下一个要处理
    }
};


//职责链中具体要处理的类
class Handler1 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER1;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler1 is handle reqest: " << req.getDescription() << endl;
    }
};
        
class Handler2 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER2;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler2 is handle reqest: " << req.getDescription() << endl;
    }
};

class Handler3 : public ChainHandler{
protected:
    bool canHandleRequest(const Reqest & req) override
    {
        return req.getReqType() == RequestType::REQ_HANDLER3;
    }
    void processRequest(const Reqest & req) override
    {
        cout << "Handler3 is handle reqest: " << req.getDescription() << endl;
    }
};

int main(){
    Handler1 h1;
    Handler2 h2;
    Handler3 h3;
    h1.setNextChain(&h2);
    h2.setNextChain(&h3);
    
    Reqest req("process task ... ", RequestType::REQ_HANDLER3);
    h1.handle(req);
    return 0;
}

[外链图片转存中…(img-mifDppys-1633924054005)]

[外链图片转存中…(img-0p6AM0Rn-1633924054006)]

[外链图片转存中…(img-Ax0WbJZd-1633924054006)]

c++设计模式

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