c++ - 使用策略模式改变方法及其关联状态

Question

我想创建一个包含状态成员和卡尔曼滤波器方法的“track”类。我喜欢使用不同类型的卡尔曼滤波器。由于每个卡尔曼滤波器的接口(interface)都是相同的，我想，我使用策略模式。我遇到的问题是，我也喜欢在更改策略时动态更改状态成员。因为使用的状态必须适合适当的卡尔曼滤波器。

这里是一个简化的代码片段:

class CVState : public StateBase { ... };
class CAState : public StateBase { ... };

卡尔曼基:

class KalmanStrategy {
public:
  virtual void Prediction(StateBase* state) = 0;
  virtual void Correction(StateBase* state) = 0;
  virtual ~KalmanStrategy(){}

protected:
  KalmanStrategy() {}
};

卡尔曼子类:

class KalmanCV : public KalmanStrategy {
public:
  KalmanCV(){}
  void Prediction(StateBase* state) {...}
  void Correction(StateBase* state) {...}
};
class KalmanCA : public KalmanStrategy {...}

这里是我的轨道类，它包含一个状态成员，必须适合卡尔曼。

class track {
public:
  track() {
    Kalman_ = new KalmanCV;
  }
  void ChangeStateModel(KalmanStrategy* K) {
     Kalman_ = K;
     //state_ = new CVState; // the state in track has to fit to the Kalman Class
                             // in this Case KalmanCV
  }
private:
  KalmanStrategy* Kalman_;
  StateBase* state_;
}

有没有办法在改变策略时也改变 state_ ？

Answer 1

你可以这样做:

struct KalmanModelCV {
  typedef KalmanCV filter_t;
  typedef StateCV state_t;
};

class track {
public:
  track() {
    filter_ = NULL;
    state_ = NULL;
  }
  typedef<typename Model>
  void ChangeModel() {
     delete filter_;
     delete state_;
     filter_ = new typename Model::filter_t();
     state_ = new typename Model::state_t();
  }
private:
  KalmanStrategy* filter_;
  StateBase* state_;
};

track t;
t.ChangeModel<KalmanModelCV>();

但是，如果每个过滤器都需要自己特定的状态类型，最好将状态的创建移至过滤器类。例如:

class KalmanStrategy {
public:
  virtual void Prediction(StateBase* state) = 0;
  virtual void Correction(StateBase* state) = 0;
  virtual StateBase* CreateState() = 0;
  virtual ~KalmanStrategy(){}

protected:
  KalmanStrategy() {}
};

class KalmanCV : public KalmanStrategy {
public:
  KalmanCV(){}
  void Prediction(StateBase* state) {...}
  void Correction(StateBase* state) {...}
  StateBase* CreateState() { return new StateCV(); } // KalmanCV only works with StateCV!
};

class track {
public:
  track() {
    filter_ = NULL;
    state_ = NULL;
  }
  void ChangeModel(KalmanStrategy* strat) {
     delete filter_;
     delete state_;
     filter_ = strat;
     state_ = strat->CreateState();
  }
private:
  KalmanStrategy* filter_;
  StateBase* state_;
};