Re: CPropertyPage OnSetActive, UpdateData, and m_bFirstSetActive

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 13 Apr 2007 15:49:11 -0500

Message-ID:

<4pqv1357fptlhhmcei6tq3o6uehabieckj@4ax.com>

On Fri, 13 Apr 2007 11:16:02 -0700, Juancho Panza <Juancho
Panza@discussions.microsoft.com> wrote:

Using VS2005 and MFC -- the help for OnSetActive() says "Your override of
this member function would typically call the default version after updating
data members, to allow it to update the page controls with the new data."

Curiously however, CPropertyPage::OnSetActive() has a BOOL m_bFirstSetActive
which prevents the UpdateData(false) from being invoked the first time.

So it's a protected BOOL and my subclass could blast it back to false after
the CommonConstruct() has set it to TRUE, or I could call the baseclass
OnSetActive() twice, or manually call UpdateData(false), but ...

Why o why does the BOOL exist in the first place ? Obviously I'm just
curious since I can code around it a number of different ways ...

When a property page is created, it receives WM_INITDIALOG, and
CDialog::OnInitDialog calls UpdateData(false). When the property sheet
receives the PSN_SETACTIVE notification, it calls OnSetActive for the newly
active page. If both are done the first time a property page is displayed,
I'd guess the intent behind m_bFirstSetActive would be to avoid calling
UpdateData(false) twice in that context.

--
Doug Harrison
Visual C++ MVP