FIX: DisplayAsDefault Ambient Property Not Updated for Control

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0

SYMPTOMS

When you use the arrow keys to change between controls in a Visual C++ 4.0 generated container, the DISPID_AMBIENT_DISPLAYASDEFAULT ambient property of the control site is not updated, and any control that relies on this property doesn't function correctly.

For example, a subclassed button control that is programmed to update its border according to the DISPID_AMBIENT_DISPLAYASDEFAULT ambient property will exhibit this behavior. In a Visual C++ generated container, the control won't update its border.

CAUSE

In Occdlg.cpp, the following line 542 shouldn't be called:

     bCheckDef = FALSE;

RESOLUTION

The best solution is to upgrade to Visual C++ 4.1. If this is not a possibility, the MFC DLL can be rebuilt without bCheckDef = FALSE; however, Microsoft recommends against this because you need to rebuild the DLL with a different name (see tech note 33).

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual C++ version 4.1.

MORE INFORMATION

Sample Code

The following code can be added to the Button Control sample shipped with Visual C++ to demonstrate this problem.

///////////////////////////////////////////////////////////////////////////

// Display the button with a thick border if appropriate

void CButtonCtrl::OnAmbientPropertyChange(DISPID dispid)

    TRACE("OnAmbientPropertyChange called\n");
    BOOL bDisplayAsDefault = FALSE;
    if(DISPID_AMBIENT_DISPLAYASDEFAULT != dispid)
        return;
    // Check the control site to see if you should add or remove the border
    if (!GetAmbientProperty(DISPID_AMBIENT_DISPLAYASDEFAULT, VT_BOOL,
            &bDisplayAsDefault))
        ASSERT(FALSE);
    if(bDisplayAsDefault)
        SendMessage(BM_SETSTYLE, BS_DEFPUSHBUTTON, 0);
    else
        SendMessage(BM_SETSTYLE, BS_PUSHBUTTON, 0);
    InvalidateControl();