Can we map a checkbox to a bool variable in MFC instead of BOOL?

Question

Take this variable mapping in a CDialog:

DDX_Check(pDX, IDC_CHECK_PREVIEW_CURRENT_WEEK, m_bPreviewCurrentWeek);

By design in the IDE it to map to a BOOL variable instead of a bool variable.

I know that under normal circumstances you can just use a bool variable wherever TRUE or FALSE is used. But, when I try changing my member variable to a bool it fails to compile on the DDX_Check routine.

Can we use bool with a checkbox control?

No. The API takes an int (or BOOL), which is not interchangeable with bool. Just make a property method `bool IsThisChecked() const {return m_bChecked != 0;}` — franji1, May 10 '22 at 21:02
No, you can't, unless you write an overloaded `DDX_Check` function that takes a `bool &` as third parameter instead of an `BOOL`. — Jabberwocky, May 11 '22 at 07:14
This question does not even make sense. How you could ever represent the `BST_INDETERMINATE` with a boolean? — sergiol, May 13 '22 at 14:15
@sergiol Because with the standard checkbox mechanism in MFC I am not using the Tri state functionality. It is a simple toggle on or off. So it does not apply. Just like it does not apply in the MFC native code. See my answer. — Andrew Truckle, May 13 '22 at 15:12

Andrew Truckle · Accepted Answer · 2022-05-11T15:03:11.577

@Jabberwocky's comment reminded me that I have already implemented some custom DDX routines:

Is it possible to map CDialog RADIO controls to an enum class object instead of int?

So I delved into the MFC source and modified a copy in my own cpp file:

void AFXAPI DDX_CheckBool(CDataExchange* pDX, int nIDC, bool& value)
{
    pDX->PrepareCtrl(nIDC);
    HWND hWndCtrl;
    pDX->m_pDlgWnd->GetDlgItem(nIDC, &hWndCtrl);
    if (pDX->m_bSaveAndValidate)
    {
        value = static_cast<bool>(::SendMessage(hWndCtrl, BM_GETCHECK, 0, 0L));
        //ASSERT(value >= 0 && value <= 2);
    }
    else
    {
        //if (value < 0 || value > 2)
        //{
        //  TRACE(traceAppMsg, 0, "Warning: dialog data checkbox value (%d) out of range.\n",
        //      value);
        //  value = 0;  // default to off
        //}
        ::SendMessage(hWndCtrl, BM_SETCHECK, static_cast<WPARAM>(value), 0L);
    }
}

I commented out the validation checks since bool has only one of two values anyway. Shout if you think that was a mistake.

So I am now able to do this:

DDX_CheckBool(pDX, IDC_CHECK_SELECT_NAMES, m_bSelectStartingNames);

It works fine.

Can we map a checkbox to a bool variable in MFC instead of BOOL?

1 Answers1