DDX_Control example for mfc - mfc

Question

I am not able to get the DDX_Control working example.
When I create the dialog box, I am not able to create a reference for the control object.
Google doesn't have examples as well.
Thanks.
void CEditDialog::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
DDX_Control(pDX, IDC_COMBO1, m_cmbBox);
DDX_Text(pDX, IDC_EDIT1, m_Edit);
}
void CMFCApplicationDDEView::OnActionEdit2()
{
// TODO: Add your command handler code here
CEditDialog dlg;
CString str;
dlg.m_cmbBox.GetLBText(0, str);
if (dlg.DoModal() == IDOK)
{
MessageBox(dlg.cmbItemStr);
}
}
dlg.m_cmbBox is NULL. Why is it null and how can I reference it in my view

Answer 1

#barmak is correct in saying that you cannot access dialog box controls directly before the InitDialog() has executed.
However, you can set / retrieve the text of the edit portion of a combo box by using DDX_CBString, like:
// in .h file
CString m_cmbItemStr;
// in .cpp
void CEditDialog::DoDataExchange(CDataExchange* pDX)
{ CDialog::DoDataExchange(pDX);
DDX_CBString(pDX, IDC_COMBO1, m_cmbItemStr);
DDX_Text(pDX, IDC_EDIT1, m_Edit);
}
void CMFCApplicationDDEView::OnActionEdit2()
{ CEditDialog dlg;
CString str = TEXT("some value");
dlg.m_cmbItemStr = str;
if (dlg.DoModal() == IDOK)
MessageBox(dlg.m_cmbItemStr);
}

Answer 2

Your code for combo box and dialog box is correct but m_cmbBox.GetLBText() cannot be used before and after DoModal() because there is no window handle. Override like code below, then access combo_str instead of accessing windows
BEGIN_MESSAGE_MAP(CEditDialog, CDialog)
ON_COMMAND(IDOK, OnOK)
//...
END_MESSAGE_MAP()
BOOL CEditDialog::OnInitDialog()
{
BOOL res = CDialog::OnInitDialog();
//Dialog is created, window handles are available, set text here
return res;
}
void CEditDialog::OnOK()
{
//get text before dialog's window handles are destroyed
int sel = m_cmbBox.GetCurSel();
if (sel >= 0) m_cmbBox.GetLBText(sel, cmbItemStr);
CDialog::OnOK();
}