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Replacing list control in a dropdown ComboBox

Posted on 1998-09-25
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Last Modified: 2013-11-19
I am trying to replace the listctrl in a CComboBox with my own dropdown window.  I am handling the CB_SHOWDROPDOWN, CBN_DROPDOWN, and CBN_CLOSEUP messages and most of the time everything works perfectly.  However, the listctrl will still popup randomly.  Is there an easy way to get a HWND to the listctrl, or is there something else I am missing?  I have traced through the messages with Spy++ and don't see anything.  Thanks.
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Question by:mcollins
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plaroche earned 200 total points
ID: 1322620
The following info is taken from the MFC FAQ:

How do I subclass the list box portion of a combo box?

The listbox portion of a combo box is of type COMBOLBOX (notice the "L").    Because the ComboLBox window is not a child of the ComboBox window, it is not obvious how to subclass the COMBOLBOX control. Luckily, under the Win32 API, Windows sends a message to the COMBOBOX (notice no "L") called WM_CTLCOLORLISTBOX before the list box is drawn. The lParam passed with this message contains the handle of the list box. For example:

LRESULT CFileUpdateCombo::OnCtlColorListBox(WPARAM wParam,
   LPARAM lParam)
{
    if ( ! m_bSubclassedListBox )
{
        HWND hWnd = (HWND)lParam;
        CWnd* pWnd = FromHandle(hWnd);
        if ( pWnd && pWnd != this )
        {
            // m_ListBox is derived from CListBox.
            m_ListBox.SubclassWindow(hWnd );
            m_ListBox.SetOwner(this);
            m_bSubclassedListBox = TRUE;
        }
    }
    return (LRESULT)GetStockObject(WHITE_BRUSH);
}

As you can see it is possible from there to get a handle to the listctrl of the combobox. In your implementation you could either subclass it with your own dropdown window or just keep that handle and disable/hide the listctrl.  The subclassing might do a better job and prevent some unusual flicker.
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by:mcollins
ID: 1322621
Thanks, plaroche.  I can't believe I didn't see that before.
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