PRB: Controls Not Initialized in CPropertyPage::OnInitDialog()

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.2

SYMPTOMS

Initializing controls in a CPropertyPage in CPropertyPage:: OnInitDialog() by way of their associated member variables doesn't work. For example, to initialize an edit control that is associated with a CString member variable called "m_strData", you could do the following:

BOOL CMyPage::OnInitDialog() {

    CPropertyPage::OnInitDialog();
    m_strData = _T("Hello");
    return TRUE;

The edit control will not be set to "Hello" at run time. This used to work in MFC 4.0 and 4.1.

CAUSE

Data is transferred from member variables to their associated controls when UpdateData() is called (UpdateData() calls DoDataExchange() which calls DDX functions). UpdateData() is called by OnInitDialog() and OnSetActive(). This caused UpdateData() to be called twice when a CPropertyPage is first created. This was a problem in MFC 4.0 and MFC 4.1. It was fixed in MFC 4.2. OnSetActive() now checks a flag (m_bFirstSetActive) to see if this is the first time it is being called. If it is the first time, then UpdateData() is not called.

As a consequence, UpdateData() will not be called again right after OnInitDialog() when OnSetActive() is called during the creation of the property page.

RESOLUTION

You can initialize member variables in the CPropertyPage's constructor or right before the call to CPropertyPage::OnInitDialog().

CMyPage::CMyPage() : CPropertyPage(CMyPage::IDD) {

    //{{AFX_DATA_INIT(CMyPage)
    m_strData = _T("Hello");
    //}}AFX_DATA_INIT

or

BOOL CMyPage::OnInitDialog() {

    m_strData = _T("Hello");
    // OnInitDialog() will call UpdateData()
    CPropertyPage::OnInitDialog();
    return TRUE;

STATUS

This behavior is by design.