Accessing parent window from a dialog in mfc

I am making a doc/view arch SDI application. I invoke a COptionsDialog in CSquaresView.

void CSquaresView::OnOptions()
{
 COptionsDialog dlg(this);
 if (dlg.DoModal() == IDOK) 
 ...
}

In COptionsDialog I want to access CSquaresView.

BOOL COptionsDialog::OnInitDialog()
{
 CDialog::OnInitDialog();
 CWnd *pParent = GetParent();
 if (pParent) {
  CSquaresView *pView = dynamic_cast<CSquaresView*>(pParent); //pView is always NULL
  if (pView != NULL) 
  {
    CSquaresDoc* pDoc = pView->GetDocument();
 ...
 }

But I always get pView as NULL; Please help me to solve this problem.

Solution

The observed behavior makes sense. A (modal) dialog's owner must be

an overlapped or pop-up window [...]; a child window cannot be an owner window.

CView-derived class instances generally are child windows. As such they cannot be the owner of a (modal) dialog. When you pass a child window into the c'tor of a CDialog-derived class, the system walks up the window hierarchy until it finds an overlapped or pop-up window, and uses that as the owner of the dialog. Regardless of whether you then call GetParent, GetAncestor, or CWnd::GetOwner, it is this true owner (usually your CFrameWnd-derived implementation) where window traversal starts.

Thus, you cannot generally use standard window traversal to find the window passed into a (modal) dialog's constructor. However, MFC records the CWnd(-derived) class instance you pass into your COptionsDialog constructor and stores it in a protected member variable m_pParentWnd, inherited from the CDialog class.

As long as COptionsDialog derives public/protected from CDialog or CDialogEx, the implementation can access this class member.

The following OnInitDialog implementation will do what you're looking for:

BOOL COptionsDialog::OnInitDialog()
{
    CDialog::OnInitDialog();
    CSquaresView *pView = dynamic_cast<CSquaresView*>(m_pParentWnd);
    if (pView != NULL) 
    {
        CSquaresDoc* pDoc = pView->GetDocument();
        ...
    }

There are other options available. For example, you could supply a COptionsDialog constructor that takes both a CWnd* and a CSquaresDoc*, delegating the first onto the base class c'tor and storing the document pointer in a (private) class member. This makes for code that's easier to follow in that it explicitly spells out, that the dialog depends on the document.