Mapping CDialog CComboBox controls to an enum class object instead of int?

Question

This question is a spin off this one (Is it possible to map CDialog RADIO controls to an enum class object instead of int?) and I am hoping that we can have a similar solution.

I have a few instances in my dialogs where I am representing an enum class as a drop-down list of options in a CComboBox (instead of using radio buttons).

Here is an example:

enum class ReportMode {
    Meeting = 0,
    Weekly
};

Currently my CComboBox is mapped to an int:

DDX_CBIndex(pDX, IDC_COMBO_REPORT_MODE, m_iReportMode);

I delved into the SDK for DDX_CBIndex:

void AFXAPI DDX_CBIndex(CDataExchange* pDX, int nIDC, int& index)
{
    pDX->PrepareCtrl(nIDC);
    HWND hWndCtrl;
    pDX->m_pDlgWnd->GetDlgItem(nIDC, &hWndCtrl);
    if (pDX->m_bSaveAndValidate)
        index = (int)::SendMessage(hWndCtrl, CB_GETCURSEL, 0, 0L);
    else

        ::SendMessage(hWndCtrl, CB_SETCURSEL, (WPARAM)index, 0L);
}

score 1 · Accepted Answer · answered Oct 16 '21 at 08:33

1

Based on the answer supplied to the linked question, I beleive this to be correct:

template<typename E>
void AFXAPI DDX_CBIndexEnum(CDataExchange* pDX, int nIDC, E& value)
{
    pDX->PrepareCtrl(nIDC);
    HWND hWndCtrl;
    pDX->m_pDlgWnd->GetDlgItem(nIDC, &hWndCtrl);
    if (pDX->m_bSaveAndValidate)
        value = static_cast<E>(::SendMessage(hWndCtrl, CB_GETCURSEL, 0, 0L));
    else
        ::SendMessage(hWndCtrl, CB_SETCURSEL, static_cast<WPARAM>(value), 0L);
}

answered Oct 16 '21 at 08:33

Andrew Truckle

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That's correct, assuming that the same requirements are met (enumerated values must start at zero, count up in increments of 1 with no gaps, and no duplicates). Also, like the linked Q&A, there's no error handling. If sending the `CB_GETCURSEL` returns a value of `CB_ERR` (-1), then that gets converted into type `E` as well. This is legal, as far as C++ is concerned, but will have repercussions in client code that may not be prepared to see enumerated values that don't have names. – IInspectable Oct 16 '21 at 08:42
@IInspectable Sure. Since this is a drop-down list the values are fixed and the combo data unsorted. So we should be OK. Thanks. – Andrew Truckle Oct 16 '21 at 08:48

Mapping CDialog CComboBox controls to an enum class object instead of int?

1 Answers1