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Altering windows message handler parameters?

Started by SiDtheTurtle Feb 21, 2005 at 11:48 AM 0 replies 400+ views

Original Post

Feb 21, 2005 at 11:48 AM

I'm trying to deal with an Directshow events, all encapsulated in a class called LDS. When I want the windows message handler to respond to these messages, I want it to call a prodcedure handleEvent which is a member function of LDS. I cannont, however, pass in an instance of the class to the message procedure, as whenever I alter the parameters, it won't work. Is is possible to alter the parameters? They are currently: LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) I want to append LDS &pLDS to the end, but it won't let me.

Evil Steve

382

Evil Steve

Feb 21, 2005 at 12:52 PM

Nope, it's not possible to alter the parameters. However, you can use SetWindowLong() and GetWindowLong() to set the 32-bit user data value associated with a HWND.

E.g:

// At startup...LPLDS pLDS;CreateWindowEx(...,pLDS);// Your window procedure...LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){LPLDS pLDS;   if(uMsg == WM_CREATE)   {      pLDS = (pLDS*)((LPCREATESTRUCT)lParam)->lpCreateParams;      SetWindowLongPtr(hWnd,GWL_USERDATA,(LONG_PTR)pLDS);   }   else      pLDS = (pLDS*)GetWindowLongPtr(hWnd,GWL_USERDATA);   // Do something with pLDS here   return DefaultWndProc(hWnd,uMsg,wParam,lParam);}

You can use a similar tecnique to wrap your window procedure in a class, for example, from my code:

LRESULT CALLBACK CStateMachine::StaticWndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){CStateMachine* pParent;	// Get pointer to app //	if(uMsg == WM_CREATE)	{		pParent = (CStateMachine*)((LPCREATESTRUCT)lParam)->lpCreateParams;		SetWindowLongPtr(hWnd,GWL_USERDATA,(LONG_PTR)pParent);	}	else	{		pParent = (CStateMachine*)GetWindowLongPtr(hWnd,GWL_USERDATA);		if(!pParent) return DefWindowProc(hWnd,uMsg,wParam,lParam);	}	pParent->m_hWnd = hWnd;	return pParent->WndProc(uMsg,wParam,lParam);}LRESULT CStateMachine::WndProc(UINT uMsg, WPARAM wParam, LPARAM lParam){   // Code here   return DefWindowProc(m_hWnd,uMsg,wParam,lParam);}

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