SetWindowLong in CustomDraw causes unhandled exception

Question

I am making some changes to a CSliderCtrl using the Custom Draw, the control is to be used in a dialog. Here is the structure: In my MessageMap I have : ON_NOTIFY_REFLECT_EX(NM_CUSTOMDRAW, OnNMCustomdraw)

The OnNMCustomdraw method looks like the following:

BOOL CCustomSliderCtrl::OnNMCustomdraw(NMHDR *pNMHDR, LRESULT *pResult)
{
    *pResult = CDRF_DODEFAULT;
    LPNMCUSTOMDRAW pNMCD = reinterpret_cast<LPNMCUSTOMDRAW>(pNMHDR);

    switch(pNMCD->dwDrawStage)
    {
        case CDDS_PREPAINT:
        {
            //Dialogs don't receive CDRF_NOTIFYITEMDRAW notifcations by returning it as part of pResult, we must
            //use the following so we ensure we receive the msg
            SetWindowLong(pNMHDR->hwndFrom, DWL_MSGRESULT, CDRF_NOTIFYITEMDRAW);
            return TRUE;
        }
        case CDDS_ITEMPREPAINT:
            if(pNMCD->dwItemSpec == TBCD_CHANNEL)
            {
                ...SNIP...
                SetWindowLong(pNMHDR->hwndFrom, DWL_MSGRESULT, CDRF_SKIPDEFAULT);
                return TRUE;
            }
    }
    return FALSE;
}

Reading around I learnt that you had to use SetWindowLong to set the return value for the custom draw, otherwise your method will not always receive the CDDS_ITEMPREPAINT message. However, when using SetWindowLong my application will never receive the CDDS_ITEMPREPAINT and so my slider just looks like a standard slider. The application crashes when any sort of interaction takes place upon the slider, such as hovering over it or minimizing and maximizing the dialog.

I snipped the TBCD_CHANNEL code as it is never reached.

When running in debug mode, it crashes at the end of the AfxUnlockGlobals method, in afxcrit.cpp. Here is a stack trace: Update: Since adding debug symbols, the crash seems to be picked up at CWnd::DefWindowProc mwthod.

comctl32.dll!_TrackBarWndProc@16()  + 0x551 bytes   
user32.dll!_InternalCallWinProc@20()  + 0x28 bytes  
user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 bytes  
user32.dll!_CallWindowProcAorW@24()  + 0x51 bytes   
user32.dll!_CallWindowProcW@20()  + 0x1b bytes  
mfc90ud.dll!CWnd::DefWindowProcW(unsigned int nMsg=15, unsigned int wParam=0, long lParam=0)  Line 1043 + 0x20 bytes    C++
mfc90ud.dll!CWnd::WindowProc(unsigned int message=15, unsigned int wParam=0, long lParam=0)  Line 1756 + 0x1c bytes C++
mfc90ud.dll!AfxCallWndProc(CWnd * pWnd=0x0012fdbc, HWND__ * hWnd=0x000308fe, unsigned int nMsg=15, unsigned int wParam=0, long lParam=0)  Line 240 + 0x1c bytes C++
mfc90ud.dll!AfxWndProc(HWND__ * hWnd=0x000308fe, unsigned int nMsg=15, unsigned int wParam=0, long lParam=0)  Line 403  C++
mfc90ud.dll!AfxWndProcBase(HWND__ * hWnd=0x000308fe, unsigned int nMsg=15, unsigned int wParam=0, long lParam=0)  Line 441 + 0x15 bytes C++
user32.dll!_InternalCallWinProc@20()  + 0x28 bytes  
user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 bytes  
user32.dll!_DispatchClientMessage@20()  + 0x4d bytes    
user32.dll!___fnDWORD@4()  + 0x24 bytes 
ntdll.dll!_KiUserCallbackDispatcher@12()  + 0x13 bytes  
user32.dll!_NtUserDispatchMessage@4()  + 0xc bytes  
user32.dll!_DispatchMessageW@4()  + 0xf bytes   
mfc90ud.dll!AfxInternalPumpMessage()  Line 183  C++
mfc90ud.dll!CWinThread::PumpMessage()  Line 900 C++
mfc90ud.dll!AfxPumpMessage()  Line 190 + 0xd bytes  C++
mfc90ud.dll!CWnd::RunModalLoop(unsigned long dwFlags=4)  Line 4386 + 0x5 bytes  C++
mfc90ud.dll!CDialog::DoModal()  Line 584 + 0xc bytes    C++
SetSelection.exe!CSetSelectionApp::InitInstance()  Line 64 + 0xb bytes  C++
mfc90ud.dll!AfxWinMain(HINSTANCE__ * hInstance=0x00400000, HINSTANCE__ * hPrevInstance=0x00000000, wchar_t * lpCmdLine=0x00020a84, int nCmdShow=1)  Line 37 + 0xd bytes C++
SetSelection.exe!wWinMain(HINSTANCE__ * hInstance=0x00400000, HINSTANCE__ * hPrevInstance=0x00000000, wchar_t * lpCmdLine=0x00020a84, int nCmdShow=1)  Line 34  C++
SetSelection.exe!__tmainCRTStartup()  Line 578 + 0x35 bytes C
SetSelection.exe!wWinMainCRTStartup()  Line 403 C
kernel32.dll!_BaseProcessStart@4()  + 0x23 bytes

So, does anyone have any insight into this matter? If you need more info just let me know.

Update: I have found a work around for now, instead of using SetWindowLong I just assign the result to pResult, then return. I force a re-draw that does repaint the sub items by calling SetRangeMin(GetRangeMin(), TRUE);, not exactly elegant but it works.

Raymond Chen Raymond Chen · Accepted Answer · 2011-08-22T04:41:45

You are calling SetWindowLong on the wrong window. The first parameter to SetWindowLong is the dialog that is handling the message, not the window that sent the message. SetWindowLong(m_hWnd, DWL_MSGRESULT, CDRF_NOTIFYITEMDRAW);.

Your code is changing the window long on the sender window, which ends up corrupting that window's private data.

SetWindowLong in CustomDraw causes unhandled exception

1 Answers