Invalid use of member (did you forget the '&' ?)

[e2easy]

I've run into a problem creating a C++ class.

I'm trying to write something based on this...

http://www.airplaysdk.com/docs.php#/api/api/ExampleS3EPointerMulti.html

The problem I'm having concerns the callback functions passed as parameters to the s3ePointerRegister(), and s3ePointerUnRegister() methods.

On each of these lines, I can a compilation error:-

"Invalid use of member (did you forget the '&' ?)"

My relevant part of my .cpp file looks like this:

void TouchHandler::registerListeners() {
	gMultiTouch = s3ePointerGetInt(S3E_POINTER_MULTI_TOUCH_AVAILABLE);
	if (gMultiTouch) {
		s3ePointerRegister(S3E_POINTER_TOUCH_EVENT, (s3eCallback)multiTouchHandler, NULL);
        s3ePointerRegister(S3E_POINTER_TOUCH_MOTION_EVENT, (s3eCallback)multiTouchMotionHandler, NULL);
	}
	else {
		s3ePointerRegister(S3E_POINTER_BUTTON_EVENT, (s3eCallback)touchHandler, NULL);
		s3ePointerRegister(S3E_POINTER_MOTION_EVENT, (s3eCallback)touchMotionHandler, NULL);
	}
}


void TouchHandler::unregisterListeners() {
	if (gMultiTouch) {
        s3ePointerUnRegister(S3E_POINTER_TOUCH_EVENT, (s3eCallback)multiTouchHandler);
        s3ePointerUnRegister(S3E_POINTER_TOUCH_MOTION_EVENT, (s3eCallback)multiTouchMotionHandler);
    }
	else {
		s3ePointerUnRegister(S3E_POINTER_BUTTON_EVENT, (s3eCallback)touchHandler);
		s3ePointerUnRegister(S3E_POINTER_MOTION_EVENT, (s3eCallback)touchMotionHandler);
	}
}

I investigated the definitions of s3ePointerRegister() and s3ePointerUnRegister(), although I don't want to change anything that side of the API. It looks like this:-

//blah
typedef int32 (*s3eCallback) (void* systemData, void* userData);
//blah blah blah
S3E_API s3eResult s3ePointerRegister(s3ePointerCallback cbid, s3eCallback fn, void* userData);
//blah
S3E_API s3eResult s3ePointerUnRegister(s3ePointerCallback cbid, s3eCallback fn);
//... 

So, how can I get around the "Invalid use..." syntax error?

[kbw]

Why are you casting?

What is the signature of multiTouchHandler, multiTouchMotionHandler, touchHandler and touchMotionHandler?

[e2easy]

Casting because s3ePointerRegister() and s3ePointerUnRegister() expect an s3eCallback parameter... and also because the example did this, and the example worked.

But sorry, yes I should have provided the signature of the callback methods. My .h file looks like this:-

#ifndef _TOUCH_HANDLER_H
#define _TOUCH_HANDLER_H

#include "s3e.h"

class TouchHandler {
	
public:

	#define MAX_TOUCHES 10

	struct CTouch {
		int32 x;
		int32 y;
		bool active;
		int32 id;
	};
	
	typedef CTouch CTouchArray [MAX_TOUCHES];
	
	TouchHandler();
	virtual ~TouchHandler();
	CTouchArray* getTouches();

	
protected:

	CTouchArray gTouches;	
	bool gMultiTouch;
	
	CTouch* getTouch(int32 id);
	void multiTouchHandler(s3ePointerTouchEvent* event);
	void multiTouchMotionHandler(s3ePointerTouchMotionEvent* event);
	void touchHandler(s3ePointerEvent* event);
	void touchMotionHandler(s3ePointerMotionEvent* event);
	void registerListeners();
	void unregisterListeners();
	
};

#endif 

[kbw]

You're trying to pass in member functions. You can only pass in static member functions as member functions get passed a this pointer, which you're not doing.

In C++, if you have to cast, you really need to stop and think if what you're doing is correct. In this case, you are not.

I would imagine you'll need something like:

class TouchHandler {
protected:
  void multiTouchMotionHandler(s3ePointerTouchMotionEvent* event);

  void registerListeners()
  {
    s3ePointerRegister(S3E_POINTER_TOUCH_EVENT, multiTouchStaticHandler, this);
  }
  void unregisterListeners()
  {
    s3ePointerUnRegister(S3E_POINTER_TOUCH_EVENT, multiTouchStaticHandler);
  }

private:
  static void multiTouchMotionStaticHandler(void *systemData, void *userData)
  {
    if (TouchHandler* pHandler = reinterpret_cast<TouchHandler*>(userData))
    {
      pHandler->multiTouchMotionHandler(reinterpret_cast<s3ePointerTouchMotionEvent*>(systemData));
    }
  }
};