C++状态模式与对象行为动态变化结合

Document

// 抽象状态接口
class Document; // 前向声明

class DocumentState {
public:
    virtual ~DocumentState() = default;
    virtual void publish(Document* doc) = 0;
    virtual void review(Document* doc) = 0;
    virtual void edit(Document* doc) = 0;
    // ... 其他状态相关行为
};

// 上下文类
class Document {
private:
    DocumentState* currentState; // 当前状态
    // ... 其他文档属性

public:
    Document();
    ~Document();

    void changeState(DocumentState* newState);

    void publish();
    void review();
    void edit();
    // ... 其他委托方法
};

// 具体状态类实现（以DraftState为例）
class DraftState : public DocumentState {
public:
    void publish(Document* doc) override; // 在这里改变文档状态到ModerationState
    void review(Document* doc) override {
        // 草稿不能直接审核
        std::cout << "Document is in Draft state, cannot be reviewed directly." << std::endl;
    }
    void edit(Document* doc) override {
        std::cout << "Editing document in Draft state." << std::endl;
        // 允许编辑
    }
};

// ... 其他具体状态类，如 ModerationState, PublishedState

// Document 构造函数和析构函数
Document::Document() {
    // 初始状态为草稿
    currentState = new DraftState();
    std::cout << "Document created in Draft state." << std::endl;
}

Document::~Document() {
    delete currentState;
}

void Document::changeState(DocumentState* newState) {
    delete currentState; // 释放旧状态
    currentState = newState; // 设置新状态
    std::cout << "Document state changed." << std::endl;
}

void Document::publish() {
    currentState->publish(this);
}

void Document::review() {
    currentState->review(this);
}

void Document::edit() {
    currentState->edit(this);
}

// DraftState 的 publish 实现
void DraftState::publish(Document* doc) {
    std::cout << "Publishing document from Draft state. Changing to Moderation." << std::endl;
    doc->changeState(new ModerationState()); // 假设ModerationState已定义
}

Document

Document

if (state == STATE_A) { ... } else if (state == STATE_B) { ... }