硬件接口之间切换的最佳设计模式

Question

我正在寻求关于我当前的方法是否有意义的建议。如果没有，我想要一些关于某种类型的设计模式的建议，可以用来取代我当前的直觉。

我的前提是我有一台相机，需要带有 CameraLink 或 CoaXPress 电缆接口的图像采集卡才能连接到 PC。相机和计算机之间的所有通信和数据传输都必须使用图像采集卡进行控制，因此这两个物理硬件对象之间的耦合非常紧密。

我的问题是我想创建一个“Camera”对象（对于GUI），它有一个“FrameGrabber”卡对象，它用来获取数据并发送/接收命令和数据。然而，我有许多不同类型的图像采集卡。我们将它们称为 CoaxGrabberA、CoaxGrabberB、LinkGrabberA 和 LinkGrabberB。与 LinkGrabber 相比，CoaxGrabber 需要一组不同的初始化参数、setter 和 getter。

因此，我认为我需要使用两个级别的继承，但从我读到的所有内容来看，继承应该很少使用，并且应该倾向于组合。因此，我非常怀疑我的设计决策，并寻求某种更好的设计。这是一些半生不熟的代码的示例。虽然有点长，但重要的部分是 CoaxGrabberA、CoaxGrabberB、LinkGrabberA 和 LinkGrabberB 是 FrameGrabber 的孙子，Camera 必须可以访问它们。其他的一切都是为了补充你可能需要的细节。

我的目标是在运行时选择我想要用于相机对象的任何帧捕获器（任何品牌/型号/接口）。此外，我想轻松访问该孙子帧捕获器类型特有的所有成员函数，以在运行时修改硬件的行为。

我的问题是“是否有一种特定的设计模式可以匹配我不知道的问题，这会让我的生活比使用我天真的、直观的方法更轻松”

//-----------------------------------------
// Parent Class
//=========================================
class FrameGrabber {
 public:
    virtual void sendCommandString(std::string cmd) = 0;
    virtual void startAcquisition() = 0;
    virtual void stopAcquisition() = 0;
};


//-----------------------------------------
// Children Classes
//=========================================
class CoaxGrabber : FrameGrabber {
 public:
    //functions unique to coax grabbers
    virtual void setCommAddress(int commAddress) = 0;   
    virtual void setStatusPort(int statusPort) = 0;    

    //functions universal to all grabbers
    virtual void sendCommandString(std::string cmd) = 0; 
    virtual void startAcquisition() = 0;                 
    virtual void stopAcquisition() = 0;  

 protected:
    int _commAddress;
    int _statusPort;        

};


class LinkGrabber : FrameGrabber {
public:
    //functions unique to link grabbers
    virtual void setBaudRate(int baudRate) = 0;
    virtual void setNumChannels(int numChannels) = 0;

    //functions universal to all grabbers
    virtual void sendCommandString(std::string cmd) = 0;    
    virtual void startAcquisition() = 0;
    virtual void stopAcquisition() = 0;

protected:
    int _baudRate;
    int _numChannels;

};


//-----------------------------------------
// Grandchildren Classes
//=========================================
class CoaxGrabberA : public CoaxGrabber {
    //identical public members as CoaxGrabber
    //different implementation using
    //different low-level API, ex: BitFlow
}


class CoaxGrabberB : public CoaxGrabber {
    //identical public members as CoaxGrabber
    //different implementation using
    //different low-level API, ex: Kaya
}


class LinkGrabberA : public LinkGrabber {
    //identical public members as LinkGrabber
    //different implementation using
    //different low-level API, ex: NationalInstruments
}


class LinkGrabberB : public LinkGrabber {
    //identical public members as LinkGrabber
    //different implementation using
    //different low-level API, ex: Imperx
}


//-----------------------------------------------------
// Finally, my Camera object, nothing too interesting here
//=====================================================
class Camera {
public:
    Camera() {
        _frameGrabber = NULL;
    }

    ~Camera() { 
        delete _frameGrabber;
    }

    void setGrabber(FrameGrabber* newGrabber)
    {
        delete _frameGrabber;
        _frameGrabber = newGrabber;
    }

    void startAcquisition() {
        _frameGrabber.startAcquisiton();
    }

    void stopAcquisition() {
        _frameGrabber.stopAcquisition();
    }

    int setSensitivity(int sens) {
        _frameGrabber.sendCommandString("sens=" + std::to_string(sens)); 
    }

private:
    FrameGrabber* _frameGrabber;

};


//-----------------------------------------
// This is why I don't like my Camera object
// the actual end-user interface smells
//=========================================
class CameraGui : QMainWindow
{
public:
    void setGrabberType(int type);
    void setCoaxGrabberCommAddress(int address);
    void setLinkGrabberBaudRate(int rate);

    CameraSystem _myCamera;
    CoaxGrabber* _myCoaxGrabber;
    LinkGrabber* _myLinkGrabber;
};


//---------------------------------------------------------------
//This function smells to me, but I cannot think of any other way
//of course, int type will be enum in actual program.
//===============================================================
void CameraGui::setGrabberType(int type) {
    switch (type) {
        case 0: 
            delete _myCoaxGrabber;
            _myCoaxGrabber = new CoaxGrabberA();
            _myCamera.setGrabber(&_myCoaxGrabber); 
            break;
        case 1: 
            delete _myCoaxGrabber;
            _myCoaxGrabber = new CoaxGrabberB();
            myCamera.setGrabber(&_myCoaxGrabber)); 
            break;
        case 2: 
            delete _myLinkGrabber;
            _myLinkGrabber = new LinkGrabberA();
            _myCamera.setGrabber(&_myLinkGrabber); 
            break;
        case 3: 
            delete _myLinkGrabber;
            _myLinkGrabber = new LinkGrabberB();
            _myCamera.setGrabber(&_myLinkGrabber); 
            break;
    }
}

//---------------------------------------------------------------
// this method of setting parameters also smells to me,
// since this data is linked to the Camera object, which
// will have no way of knowing whether the state of its
// framegrabber changed... furthermore, if I change framegrabbers,
// none of the parameter settings (state) will be remembered.
// the user will need to set them all over again.
// the only way I know to circumvent this is to allocate memory for
// every type of framegrabber, and broadcast all state changes to
// all applicable parent grabbers, which will reside in permanent
// memory until the application closes.
//===============================================================
void CameraGui::setCoaxGrabberCommAddress(int address) {
    if(myCoaxGrabber != NULL) {
        myCoaxGrabber->setCommAddress(address);
    }
}

//likewise smell
void CameraGui::setLinkGrabberBaudRate(int rate) {
    if(myLinkGrabber != NULL) {
        myLinkGrabber->setBaudRate(rate);
    }
}

任何和所有的建议将不胜感激。长话短说，我对 OO 设计模式知之甚少，但这感觉像是一个已解决的问题，而且我感觉我正在重新发明轮子。有没有更好、更成熟的方法来实现我想做的事情？

Answer 1

您的设计模式称为“工厂”，继承没有任何问题（https://en.wikipedia.org/wiki/Factory_method_pattern）

在继承和聚合之间进行选择时我们应该使用的经验法则：

• 如果某些东西反映了“是”关系（例如 CoaxGrabber 是 FrameGrabber），请使用继承。
• 如果某些东西反映“有”关系（例如CameraGui有FrameGrabber），请使用聚合。

我建议使用智能指针（例如 std::shared_ptr）而不是 new 并删除当前正在使用的指针，这将使代码更易于管理且不易出错。

在这种情况下：

class Camera {
public:
    CameraSystem() {} // don't need explicit initialization

    ~CameraSystem() {} // resource in shared_ptr will be deleted automatically

    void setGrabber(const std::shared_ptr<FrameGrabber>& newGrabber)
    {
        _frameGrabber = newGrabber;
    }

    void startAcquisition() {
        _frameGrabber->startAcquisiton(); // note -> instead of .
    }

    // ....

private:
    std::shared_ptr<FrameGrabber> _frameGrabber;
};

如果使用工厂：

void CameraGui::setGrabberType(int type) {
    _myCamera.setGrabber(GrabberFactory::createGrabber(type));
}

class GrabberFactory {
public:
    std::shared_ptr<FrameGrabber> createGrabber(int type) {
        switch (type) {
        case GrabberTypeCoaxA: return {new CoaxGrabberA()};
        case GrabberTypeCoaxB: return {new CoaxGrabberB()}; 
        default: throw std::invalid_argument("Invalid grabber type");
        }
    }
};