Sakura Sakura - 3 months ago 21
C++ Question

Owner draw listbox alway return (LPDRAWITEMSTRUCT)->itemID = -1

I created an owner draw listbox. Do you know why in WM_DRAWITEM message, I only receive

(LPDRAWITEMSTRUCT)lParam->itemID = -1
?

I'm coding with VS 2010 C++ Express and Win 7.

Create listbox and set scroll info:

lbHWND = CreateWindowExW(NULL, WC_LISTBOX, NULL,
WS_CHILD | WS_BORDER | WS_VISIBLE | LBS_NODATA |
LBS_OWNERDRAWFIXED | LBS_NOTIFY | LBS_NOINTEGRALHEIGHT,
0, 0, 400, 400, tkHWND, (HMENU)IDC_LISTBOX_ENTRY, hInstance, 0);

SCROLLINFO lbSi = { 0 };
lbSi.cbSize = sizeof(SCROLLINFO);
lbSi.fMask = SIF_RANGE | SIF_PAGE | SIF_POS;
lbSi.nMin = 0;
lbSi.nMax = 1000;
lbSi.nPage = 20;
lbSi.nPos = 0;
SetScrollInfo(lbHWND, SB_VERT, &lbSi, TRUE);


WinProc:

LRESULT CALLBACK WndProc(HWND phwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_MEASUREITEM:
{
MEASUREITEMSTRUCT* lpmis = (LPMEASUREITEMSTRUCT)lParam;
switch (lpmis->CtlID)
{
case IDC_LISTBOX_ENTRY:
lpmis->itemHeight = 20;
break;
default:
break;
}
return TRUE;
}
case WM_DRAWITEM:
{
DRAWITEMSTRUCT* lpdis = (LPDRAWITEMSTRUCT)lParam;

// Check lpdis->itemID, for test purpose only
FILE *f;
if (!_wfopen_s(&f, L"E:\\lb.txt", L"ab"))
{
fprintf(f,"%d\r\n", lpdis->itemID);
fclose(f);
}
// lpdis->itemID always = -1
return TRUE;
}
}
}

Answer

I have find the answer: For an owner draw listbox with LBS_NODATA style, I have to tell the listbox number of items it has.

SendMessage(lbHWND, LB_RESETCONTENT, 0, 0);    // Remove all items, if have any
SendMessage(lbHWND, LB_SETCOUNT, 1000, 0);     // Set number of items (here is 1000)