如何通过 C++/CLI 在 C# 中覆盖 C++ 虚拟方法（不在接口类中）

Question

作为参考，此问题涉及通过 C# 访问 C++ NaturalPoint Camera SDK。

我正在尝试将虚拟方法的实现从 C++ 传递到 C#。我遇到的问题是 C++ 虚拟方法不在接口类中，我无法更改它。这是类声明：

class CLAPI cCameraListener
{
public:
    cCameraListener()  {};
    ~cCameraListener() {};

    virtual void FrameAvailable();
    virtual void FrameOverflow();
    virtual void ButtonPressed();
};

CLAPI 定义为：

#define CLAPI __declspec(dllexport)

我不能从 ref 类中的 cCameraListener 类继承，因为它不是接口类，也没有想出任何方法将虚拟方法公开给托管类。我还需要能够注册我在下面详细讨论的侦听器。

这是用于侦听帧的 C++ 实现：

// process frames as they arrive
class FrameListener: public cCameraListener
{
public:
  Camera *myCamera;
  FrameListener(Camera *cameraPtr)
  {
    myCamera = cameraPtr;
  };

  void FrameAvailable()
  {
    Frame *thisFrame = myCamera->GetFrame();

    // do something with the frame here

    thisFrame->Release();
  };
};

int _tmain(int argc, _TCHAR* argv[])
{
  // startup camera
  CameraManager::X().WaitForInitialization();
  Camera *camera = CameraManager::X().GetCamera();
  if(camera==0)
  {
      // print an error
      return 1;
  }

  // set camera properties
  camera->SendEmptyFrames(false);
  camera->SendInvalidFrames(false);
  camera->SetVideoType(SegmentMode);

  // setup frame listener
  FrameListener *myListener = new FrameListener(camera);
  camera->AttachListener(myListener);

  // start the camera
  camera->Start();

  // while loop holding thread

  // clean up
  camera->Release();
  CameraManager::X().Shutdown();

  return 0;
}

以下是一些现有的 C++/CLI 包装器代码： 链接：https://code.google.com/p/npcamerasdkdotnet/

public ref class MCamera{
public:

  MCamera(Camera * camera){
    this->camera = camera;

  }
  ~MCamera(){
    delete this->camera;
  }

  void        Start(){camera->Start();} 

  void        SetExposure(int Value){camera->SetExposure(Value);}          
  void        SetThreshold(int Value){camera->SetThreshold(Value);}        
  void        SetIntensity(int Value){camera->SetIntensity(Value);}

  // TODO - WRAP THESE METHODS
  //void AttachListener(cCameraListener * Listener);
  //void RemoveListener(cCameraListener * Listener);

  // other wrapped methods here...

private:
  Camera * camera;
};

请注意，在 MCamera 包装类中，需要实现 AttachListener 方法，并且需要一个指向上述 cCameraListener 类的指针。

任何建议将不胜感激！谢谢！

Answer 1

解决方案并不难，您需要将侦听器包装在管理类中，如下所示：

class CameraListenerImp;

/**
 * Managed Version of the listener which will be used by managed clients
 */
public ref class ManagedCameraListener abstract 
{
public:
        ManagedCameraListener();

    virtual void FrameAvailable() abstract;
    virtual void FrameOverflow() abstract;
    virtual void ButtonPressed() abstract;

    ~ManagedCameraListener();

    CameraListenerImp* GetUnManagedListener()
    {
        return _unmanagedListener;
    }


private:
    CameraListenerImp*  _unmanagedListener;
};

// Unmanaged to managed listener wraper
class CameraListenerImp : public cCameraListener
{
public:
    CameraListenerImp( ManagedCameraListener^ in )
    {
        theClass = in;
    }
    virtual void FrameAvailable()
    {
        theClass->FrameAvailable();
    }
        virtual void FrameOverflow()
    {
        theClass->FrameOverflow();
    }
        virtual void ButtonPressed()
    {
        theClass->ButtonPressed();
    }
private:
    gcroot < ManagedCameraListener^ > theClass;
};

///////////////////////////////////////////////////////////
// ManagedCameraListener imp
ManagedCameraListener::ManagedCameraListener()
{
    _unmanagedListener = new CameraListenerImp( this );
}

ManagedCameraListener::~ManagedCameraListener()
{
    delete _unmanagedListener;
}
///////////////////////////////////////////////////////////
// ManagedCameraListener imp end

public ref class MCamera
{
public:
    MCamera(Camera * camera)
    {
        this->camera = camera;
    }
    ~MCamera()
    {
        delete this->camera;
    }

    void AttachListener( ManagedCameraListener^ listener )
    {
            // call unmanaged version of the AttachListener
            this->camera->AttachListener( listener->GetUnManagedListener() );
    }

    void RemoveListener( ManagedCameraListener^ listener )
    {
            // call unmanaged version of the RemoveListener
            this->camera->RemoveListener( listener->GetUnManagedListener() );
    }


private:
  Camera * camera;
};

/**
 * Managed implementation
 */
public ref class MyOwnManagedCameraListener : public ManagedCameraListener
{
public:
     virtual void FrameAvailable() override { / do something hard / }
     virtual void FrameOverflow() override { / do something hard / }
     virtual void ButtonPressed() override { / do something hard */ }
};

int main(array ^args)
{
    MCamera^ cam = gcnew MCamera( camera );
    MyOwnManagedCameraListener^ listener = gcnew MyOwnManagedCameraListener();

cam->AttachListener( listener );
cam->RemoveListener( listener );
return 0;

}