c++ - 在硬件接口(interface)之间切换的最佳设计模式

Question

我正在就我当前的方法是否合理征求意见。如果没有，我想要一些关于某种类型的设计模式的建议，而不是用来取代我目前的直觉。

我的前提是，我有一个相机，它需要一个带有 CameraLink 或 CoaXPress 电缆接口(interface)的图像采集卡来连接到 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(用于 GUI)，它有一个“FrameGrabber”卡对象，用于获取数据和发送/接收命令和数据.但是，我有许多不同类型的图像采集卡。我们称它们为 CoaxGrabberA、CoaxGrabberB、LinkGrabberA 和 LinkGrabberB。与 LinkGrabbers 相比，CoaxGrabbers 需要一组不同的初始化、setter 和 getter 参数。

因此，我认为我需要使用两级继承，但从我读过的所有内容来看，应该很少使用继承，应该优先使用组合。因此，我非常怀疑我的设计决定，并寻求某种更好的设计。这是一些半生不熟的代码示例。它有点冗长，但重要的部分是 CoaxGrabberA、CoaxGrabberB、LinkGrabberA 和 LinkGrabberB 是 FrameGrabber 的孙子的概念，Camera 必须可以访问它们。其他一切都是为了填写您可能需要的详细信息。

我的目标 是在运行时选择我想用于我的 Camera 对象的任何 framegrabber(任何品牌/型号/接口(interface))。此外，我想轻松访问该孙代 framegrabber 类型独有的所有成员函数，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解决我不知道的问题，这比使用我天真的、直观的方法更容易”

//-----------------------------------------
// 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);
    }
}

我们将不胜感激任何和所有的建议。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，我觉得我正在重新发明轮子。是否有更好、更成熟的方法来实现我正在尝试做的事情？

Answer 1

你的设计模式叫做“工厂”，继承没有错(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:

• 如果某物反射(reflect)"is"关系(例如 CoaxGrabber 是 FrameGrabber)，则使用继承。
• 如果某物反射(reflect)“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");
        }
    }
};