Using CALLBACK in a class

[RichardF]

Hi,

Can a CALLBACK function, eg a window procedure, be a class method ?

eg
class CMyWinApp {
public:
CMyWinApp();
~CMyWinApp();

....

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
};

Thanks.

 

[LazyMe]

No it can't. If you want it to be part of a class, it must be a static method. The windows API is not OO and does not understand the "this" prefix of the member method.....
Greetings,
Rick

 

[RichardF]

but this is ok ?

class CMyWinApp {
public:
CMyWinApp();
~CMyWinApp();

....

static LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
};

 

[LazyMe]

Yes, that's ok.
Although you will have to make some sort of object map so you can distinguish between objects when receiving messages....
Greetings,
Rick

 

[Cagliostro]

class CMyWinApp {
public:
CMyWinApp()
{...SetWindowLong(hWnd, GWL_USERDATA, (LONG)this);....}
~CMyWinApp();

....

static LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
};

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
if(hWnd)
CMyWinApp* theObj = (CMyWinApp*)(void*)GetWindowLong(hWnd, GWL_USERDATA);
if(theObj)use theObj here
}
Ion Filipski

filipski@excite.com

 

[RichardF]

ok, i got it. thanks.