CDialog - EndDialog from a MODELESS dialog? - winapi

Question

The MS documentation (and others) "clearly" states:
... Because the normal OnOk and OnCancel member functions of a CDialog
object would call EndDialog, make sure your modeless dialog box does
not call those functions and instead overrides
Since CDialog::OnOk effectively calls CDialog::EndDialog, and that method looks like:
void CDialog::EndDialog(int nResult)
{
ASSERT(::IsWindow(m_hWnd));
if (m_nFlags & (WF_MODALLOOP|WF_CONTINUEMODAL))
EndModalLoop(nResult);
::EndDialog(m_hWnd, nResult);
}
we can also check the docs for ::EndDialog which again "clearly" state:
Dialog boxes created by the DialogBox, DialogBoxParam,
DialogBoxIndirect, and DialogBoxIndirectParam functions must be
destroyed using the EndDialog function. An application calls EndDialog
from within the dialog box procedure; the function must not be used
for any other purpose.
Yet, I have a CDialog derived class that has it's default behavior wrt. OnOKand seemingly everything is working when I use it non-modal / modeless.
That is:
* When I close the (modeless) dialog, it is closed/removed from view.
* The application doesn't show any memory leaks. (MFC debug build)
So what? Do I need to prevent EndDialog and call DestroyWindow myself or not?
Note: I know what the docs and "the web" says. It's just that I haven't yet found why I need to do it differently, and this one class should be usable for modeless and modal mode, so not having to do anything different might be handy.

Answer 1

The MSDN Docs for CDialog::OnOK clearly states
If you implement the OK button in a modeless dialog box, you must
override the OnOK method and call DestroyWindow inside it. Do not call
the base-class method, because it calls EndDialog which makes the
dialog box invisible but does not destroy it
So you would need to override CDialog::OnOK and call DestroyWindow() inside -- here's a modified example from MSDN:
class CDlg : public CDialog
{
...
BOOL m_bModal;
...
}
CDlg::CDlg(CWnd* pParent /*=NULL*/)
: CDialog(CDlg::IDD, pParent)
{
...
m_bModal = FALSE;
...
}
INT_PTR CDlg::DoModal()
{ m_bModal = TRUE;
const INT_PTR rval = CDialog::DoModal();
m_bModal = FALSE;
return rval;
}
void CDlg::OnOK()
{
if (!UpdateData(TRUE))
{
TRACE(_T("UpdateData failed during dialog termination\n"));
// The UpdateData routine will set focus to correct item
return;
}
if (m_bModal)
EndDialog(IDOK);
else
DestroyWindow();
}
void CDlg::OnCancel()
{
if (m_bModal)
EndDialog(IDCANCEL);
else
DestroyWindow();
}