Question

How do I get a 3-state checkbox to use a different bitmap for the Indeterminate state?

I want to change the image used by my 3-state checkboxes to use a different one; the controls are in Win98-style, and the indeterminate state of such checkboxes is difficult to distinguish from disabled checkboxes (this is presumably why they changed this for the WinXP-style controls, but I cannot use those because of other details in my project).

I’m using Visual C++ 2010, and I’ve defined an 8×8 bitmap in VS’s Resource Editor. The bitmap’s ID is IDB_INDET_CHECK.

I’m not entirely sure what the standard “technique” for something like this is; I’ve only really just started getting into manipulating Windows controls and MFC.

My first attempt was to create a class, CTriButton, that derives from CButton, override the DrawItem function, and try to draw it myself. I then used SubclassDlgItem to turn one of the checkboxes in my window into this class (I think?). This… sort of works? The checkbox no longer appears, and if I click on where it should be, an empty checkbox frame appears, but nothing else happens (and the debug message in my code is not being sent).

Here’s the relevant code, though I’m not sure any of this is right. First, code from my window’s OnInitDialog.

BOOL CAffixFilterDlg::OnInitDialog() // CAffixFilterDlg is my CDialog-derived window
{
    CDialog::OnInitDialog(); // call basic version

    // subclass a CButton-derived control with CTriButton
    if ( CBipedHead.SubclassDlgItem(IDC_HEAD, this) ) // CBipedHead is a CTriButton member of CAffixFilterDlg, IDC_HEAD is a checkbox
        SetWindowLong(CBipedHead.m_hWnd, GWL_STYLE, CBipedHead.GetStyle() | BS_OWNERDRAW); // set the ownerdraw style
    else // subclassing didn't work
        _ERROR("Subclassing failed."); // I do not see this error message, so SubclassDlgItem worked?

    // initialization continues, but is not relevant...
    UpdateWindow();
    Invalidate();

    return TRUE;
}

Next, the code for my custom button’s DrawItem.

void CTriButton::DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct)
{
    _DMESSAGE("Drawing TriButton"); // never see this message

    CDC dc;
    dc.Attach(lpDrawItemStruct->hDC);     //Get device context object
    int nWidth = GetSystemMetrics(SM_CXMENUCHECK);
    int nMargin = ( nWidth - 8 ) / 2;

    CRect textRt = lpDrawItemStruct->rcItem;
    textRt.right = textRt.right - nWidth - nMargin;

    CString text;
    GetWindowText(text);

    UINT textDrawState = DST_TEXT;
    if ( lpDrawItemStruct->itemState & ODS_DISABLED )
        textDrawState |= DSS_DISABLED;

    dc.DrawState(CPoint(textRt.left, textRt.top), textRt.Size(), text, textDrawState, TRUE, 0, (CBrush*)NULL);

    CRect rt = lpDrawItemStruct->rcItem;    // initial rect is for entire button
    rt.left = rt.right - nWidth;            // set left margin
    LONG center = ( rt.bottom + rt.top ) / 2;
    rt.top = center - nWidth/2;
    rt.bottom = center + nWidth/2;

    UINT checkDrawState = DFCS_BUTTONCHECK;
    if ( lpDrawItemStruct->itemState & ODS_DISABLED )
        checkDrawState |= DFCS_INACTIVE;

    if ( lpDrawItemStruct->itemState & ODS_CHECKED )
        checkDrawState |= DFCS_CHECKED;

    else if ( GetCheck() == BST_INDETERMINATE ) {
        _VMESSAGE("Indeterminate; custom draw.");

        CBitmap indet_check = CBitmap();
        indet_check.LoadBitmap(IDB_INDET_CHECK);

        CPoint pt = CPoint(rt.left + nMargin, rt.top + nMargin);
        CSize sz = CSize(8, 8);

        dc.DrawState(pt, sz, &indet_check, DST_BITMAP|DSS_NORMAL);
    }

    dc.DrawFrameControl(rt, DFC_BUTTON, checkDrawState);
}

Answer 1

Not the answer, but an answer: this custom CCheckBox I found more-or-less enables what I want. It doesn’t, by default, allow 3 states, but I fixed that up with some of my own tweaks. I’m not 100% sure it works out of the box (I’ve had some issues, that don’t seem to be due to my edits, but I can’t be sure), but it was the solution I’ve used. I’m not going to call this the answer, though, in case someone can spy what was wrong with my code and wants to illuminate me.