Struct for WM_DRAWITEM Message

[SteveMurphy]

I have to send a WM_DRAWITEM message to a listbox. The documentation says that the lParam is the DRAWITEMSTRUCT for the item to be drawn.

Is there a function I can call to populate the members of the struct before issuing the call?

Thanks.

[HeartBreakKid]

Generally, you will not send WM_DRAWITEM messages. I can't think of any good reason to. If you need to repaint a control, you can call Invalidate(), InvalidateRect(), or in the case of a List control call RedrawItems().

[NoHero]

I don't think so, I think you must initialize this structure on your own:


DRAWITEMSTRUCT it;

ZeroMemory(&it, sizeof(DRAWITEMSTRUCT));

it.CtlType = ODT_LISTBOX;
it.CtlID = IDC_LISTBOX; // Insert the resource identifier of your list box here
it.itemID = 0; // Item to be drawn
it.itemAction = ODA_SELECT; // See MSDN for more flags here. This will draw the item selected
it.itemState = ODS_SELECTED; // More flags > look at MSDN
it.hwndItem = GetDlgItem(IDC_LISTBOX);
it.hDC = GetDC(it.hwndItem);
GetWindowRect(it.rcItem); // Rectangle of your listbox
it.itemData = 0; // If you want to associate some data with the item


Haven't figured it out, but it should work :wave:

[NoHero]

Generally, you will not send WM_DRAWITEM messages. I can't think of any good reason to. If you need to repaint a control, you can call Invalidate(), InvalidateRect(), or in the case of a List control call RedrawItems().

Of course, redrawing only one item is much more efficent if you have a ton of items. So this can be quiet helpful. RedrawItem is the most efficient of course, it allows you the same. So I think this is the proper solution.

[SteveMurphy]

Thanks everybody.

To keep it simple, I decided to first try the InvalidateRect suggested by HeartBreakKid. Also, I'm not using MFC, so I can't use RedrawItems.

My app compiles/links fine, but it crashes. Please look at the following code and tell me if you see errors:

LPRECT pRect = 0;
SendMessage(m_hListBox,LB_GETITEMRECT, (WPARAM) idx, (LPARAM) pRect);
InvalidateRect(m_hListBox,pRect,TRUE);
UpdateWindow(m_hListBox);

TIA