介紹

? ? ? ? 狀態(tài)模式允許一個(gè)對(duì)象在其內(nèi)部狀態(tài)改變時(shí)改變它的行為，對(duì)象看起來(lái)似乎修改了它的類。其別名為狀態(tài)對(duì)象，狀態(tài)模式是一種對(duì)象行為模式。

實(shí)現(xiàn)

myclass.h

//
// Created by yuwp on 2024/1/12.
//

#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H

#include <iostream>
#include <unordered_map>
#include <atomic>
#include <vector>
#include <memory>

class State {   // 抽象狀態(tài)類
public:
    virtual void handle() = 0;
};

class Context { // 環(huán)境類
public:
    Context();
    void setState(const std::shared_ptr<State> &state);
    void request(int num);
    void changeState();

private:
    std::shared_ptr<State> m_state;
    int m_value;
};

class ConcreteStateA : public State {    // 具體狀態(tài)類A
public:
    void handle() override;
};

class ConcreteStateB : public State {    // 具體狀態(tài)類B
public:
    void handle() override;
};


#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//

#include "myclass.h"
#include <thread>
#include <unistd.h>
#include <sstream>

Context::Context() {
    m_value = 0;
    m_state.reset(new ConcreteStateA());
}

void Context::setState(const std::shared_ptr<State> &state) {
    m_state = state;
}

void Context::request(int num) {
    int tmp = m_value;
    m_value += num;
    if ((tmp >= 0 && m_value < 0) || (tmp < 0 && m_value >= 0)) {
        changeState();
    }
    m_state->handle();
}

void Context::changeState() {
    std::cout << "切換狀態(tài)" << std::endl;
    if (m_value >= 0) {
        m_state.reset(new ConcreteStateA());
    } else {
        m_state.reset(new ConcreteStateB());
    }
}

void ConcreteStateA::handle() {
    std::cout << "ConcreteStateA::handle()" << std::endl;
}

void ConcreteStateB::handle() {
    std::cout << "ConcreteStateB::handle()" << std::endl;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"

int main() {
    Context *context = new Context;
    context->request(0);
    std::cout << "-------------------" << std::endl;
    context->request(-10);
    std::cout << "-------------------" << std::endl;
    context->request(20);

    return 0;
}

總結(jié)

優(yōu)點(diǎn)

? ? ? ? 1.?封裝了狀態(tài)的轉(zhuǎn)換規(guī)則。在狀態(tài)模式中可以將狀態(tài)的轉(zhuǎn)換代碼封裝在環(huán)境類或者具體狀態(tài)類中，對(duì)狀態(tài)轉(zhuǎn)換代碼進(jìn)行集中管理，而不是分散在一個(gè)個(gè)業(yè)務(wù)方法中。

? ? ? ? 2.?將所有與某個(gè)狀態(tài)有關(guān)的行為放到一個(gè)類中，只需要注入一個(gè)不同的狀態(tài)對(duì)象即可使環(huán)境對(duì)象擁有不同的行為。

? ? ? ? 3.?允許狀態(tài)轉(zhuǎn)換邏輯與狀態(tài)對(duì)象合成一體，而不是提供一個(gè)巨大的條件語(yǔ)句塊。狀態(tài)模式可以避免使用龐大的條件語(yǔ)句來(lái)將業(yè)務(wù)方法和狀態(tài)轉(zhuǎn)換代碼交織在一起。

? ? ? ? 4.?可以讓多個(gè)環(huán)境對(duì)象共享一個(gè)狀態(tài)對(duì)象，從而減少系統(tǒng)中對(duì)象的個(gè)數(shù)。

缺點(diǎn)

? ? ? ? 1.?狀態(tài)模式的使用必然會(huì)增加系統(tǒng)中類和對(duì)象的個(gè)數(shù)，導(dǎo)致系統(tǒng)運(yùn)行開(kāi)銷增大。

? ? ? ? 2.?狀態(tài)模式的程序結(jié)構(gòu)與實(shí)現(xiàn)都較為復(fù)雜，如果使用不當(dāng)將導(dǎo)致程序結(jié)構(gòu)和代碼的混亂，增加系統(tǒng)設(shè)計(jì)的難度。

? ? ? ? 3.?狀態(tài)模式對(duì)開(kāi)閉原則的支持并不太好。增加新的狀態(tài)類需要修改那些負(fù)責(zé)狀態(tài)轉(zhuǎn)換的源代碼，否則無(wú)法轉(zhuǎn)換到新增狀態(tài)；而且修改某個(gè)狀態(tài)類的行為也需修改對(duì)應(yīng)類的源代碼。

適用場(chǎng)景

? ? ? ? 1.?對(duì)象的行為依賴于它的狀態(tài)（例如某些屬性值），狀態(tài)的改變將導(dǎo)致行為的變化。

? ? ? ? 2.?在代碼中包含大量與對(duì)象狀態(tài)有關(guān)的條件語(yǔ)句。這些條件語(yǔ)句的出現(xiàn)，會(huì)導(dǎo)致代碼的可維護(hù)性和靈活性變差，不能方便地增加和刪除狀態(tài)，并且導(dǎo)致客戶類與類庫(kù)之間的耦合增強(qiáng)。

練習(xí)

myclass.h

//
// Created by yuwp on 2024/1/12.
//

#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H

#include <iostream>
#include <unordered_map>
#include <atomic>
#include <vector>
#include <memory>

class Level {   // 抽象狀態(tài)類
public:
    virtual void play() = 0;
    virtual void doubleScore();
    virtual void changeCards();
    virtual void peekCards();
};

class CardsGame {
public:
    CardsGame();
    ~CardsGame();

    void play(int score);   // 模擬玩游戲得分
    void doubleScore();
    void changeCards();
    void peekCards();

private:
    Level *m_level;     // 當(dāng)前等級(jí)
    Level *m_primary;   // 入門級(jí)
    Level *m_secondary; // 熟練級(jí)
    Level *m_professional;  // 高手級(jí)
    Level *m_final;     // 骨灰級(jí)
    int m_score;    // 得分
};

class PrimaryLevel : public Level {
public:
    void play() override;

    void doubleScore() override;

    void changeCards() override;

    void peekCards() override;
};

class SecondaryLevel : public Level {
public:
    void play() override;

    void changeCards() override;

    void peekCards() override;
};

class ProfessionalLevel : public Level {
public:
    void play() override;

    void peekCards() override;
};

class FinalLevel : public Level {
public:
    void play() override;
};


#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//

#include "myclass.h"
#include <thread>
#include <unistd.h>
#include <sstream>

void Level::doubleScore() {
    std::cout << "勝利積分加倍" << std::endl;
}

void Level::changeCards() {
    std::cout << "換牌" << std::endl;
}

void Level::peekCards() {
    std::cout << "偷看他人的牌" << std::endl;
}

CardsGame::CardsGame() {
    m_primary = new PrimaryLevel();
    m_secondary = new SecondaryLevel();
    m_professional = new ProfessionalLevel();
    m_final = new FinalLevel();
    m_level = m_primary;
    m_score = 0;
}

CardsGame::~CardsGame() {
    if (m_primary) {
        delete m_primary;
    }
    if (m_secondary) {
        delete m_secondary;
    }
    if (m_professional) {
        delete m_professional;
    }
    if (m_final) {
        delete m_final;
    }
}

void CardsGame::play(int score) {
    m_level->play();
    m_score += score;
    if (m_score < 100) {
        if (m_level != m_primary) {
            std::cout << "切換到入門級(jí)" << std::endl;
            m_level = m_primary;
        }
    } else if (m_score < 500) {
        if (m_level != m_secondary) {
            std::cout << "切換到熟練級(jí)" << std::endl;
            m_level = m_secondary;
        }
    } else if (m_score < 1000) {
        if (m_level != m_professional) {
            std::cout << "切換到高手級(jí)" << std::endl;
            m_level = m_professional;
        }
    } else {
        if (m_level != m_final) {
            std::cout << "切換到骨灰級(jí)" << std::endl;
            m_level = m_final;
        }
    }
}

void CardsGame::changeCards() {
    m_level->changeCards();
}

void CardsGame::doubleScore() {
    m_level->doubleScore();
}

void CardsGame::peekCards() {
    m_level->peekCards();
}

void PrimaryLevel::play() {
    std::cout << "入門級(jí)游戲開(kāi)始" << std::endl;
}

void PrimaryLevel::doubleScore() {
    std::cout << "入門級(jí)不支持游戲勝利積分加倍功能" << std::endl;
}

void PrimaryLevel::changeCards() {
    std::cout << "入門級(jí)不支持換牌功能" << std::endl;
}

void PrimaryLevel::peekCards() {
    std::cout << "入門級(jí)不支持偷看他人的牌功能" << std::endl;
}

void SecondaryLevel::play() {
    std::cout << "熟練級(jí)游戲開(kāi)始" << std::endl;
}

void SecondaryLevel::changeCards() {
    std::cout << "熟練級(jí)不支持換牌功能" << std::endl;
}

void SecondaryLevel::peekCards() {
    std::cout << "熟練級(jí)不支持偷看他人的牌功能" << std::endl;
}

void ProfessionalLevel::play() {
    std::cout << "高手級(jí)游戲開(kāi)始" << std::endl;
}

void ProfessionalLevel::peekCards() {
    std::cout << "高手級(jí)不支持偷看他人的牌功能" << std::endl;
}

void FinalLevel::play() {
    std::cout << "骨灰級(jí)游戲開(kāi)始" << std::endl;
}

main.cpp文章來(lái)源地址http://www.zghlxwxcb.cn/news/detail-824368.html

#include <iostream>
#include <mutex>
#include "myclass.h"

int main() {
    CardsGame *cardsGame = new CardsGame();
    cardsGame->doubleScore();
    cardsGame->changeCards();
    cardsGame->peekCards();
    cardsGame->play(200);
    std::cout << "------------------------" << std::endl;
    cardsGame->doubleScore();
    cardsGame->changeCards();
    cardsGame->peekCards();
    cardsGame->play(500);
    std::cout << "------------------------" << std::endl;
    cardsGame->doubleScore();
    cardsGame->changeCards();
    cardsGame->peekCards();
    cardsGame->play(500);
    std::cout << "------------------------" << std::endl;
    cardsGame->doubleScore();
    cardsGame->changeCards();
    cardsGame->peekCards();
    cardsGame->play(0);

    delete cardsGame;

    return 0;
}

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