PRB: Appearance Property Uses Windows 4.0 WS_EX_CLIENTEDGE

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with: Microsoft Visual C++, 32-bit Edition, versions 4.0, 4.1

SYMPTOMS

MFC Controls support a set of standard properties. One of these properties is Appearance (DISPID_APPEARANCE). Appearance is implemented to give a control a 3-D look. If the control is used on a version of Windows or Windows NT less than 4.0, the Appearance property will not affect the appearance of the control at run time.

CAUSE

At run time, the Appearance property is implemented in an MFC control by setting an extended window style WS_EX_CLIENTEDGE. This window style is not supported on versions of Windows or Windows NT less than 4.0.

RESOLUTION

It is possible to supply your own implementation of the Appearance property although this technique will not work for subclassed Windows controls.

STATUS

This behavior is by design.

MORE INFORMATION

Using the Class Wizard, add the stock Appearance property but choose Get/Set methods rather that accepting the stock implementation. In the control, declare a member variable of type BOOL to represent the Appearance property. The stock Get/Set functions can be copied and changed slightly to manipulate this variable as well as handle the property binding requirements. In the Draw function, draw a 3-D border depending on the value of this variable.

Sample Code

   // these get and set functions are the same as the original with a minor
   // change (noted in the code)

   short CTestAppearanceCtrl::GetAppearance()
   {
       return m_MyAppearance;
   }

   void CTestAppearanceCtrl::SetAppearance(short nNewValue)
   {
       if (nNewValue != 0 && nNewValue != 1)
           ThrowError(CTL_E_INVALIDPROPERTYVALUE,
                      AFX_IDP_E_INVALIDPROPERTYVALUE);

       // Is the property changing?
       if (m_MyAppearance == nNewValue)
           return;

       if (!BoundPropertyRequestEdit(DISPID_APPEARANCE))
           SetNotPermitted();

   // changed from original
       // do not use the WS_EX_CLIENTEDGE style
       //ASSERT((m_hWnd == NULL) ||
       //  ((GetExStyle() & WS_EX_CLIENTEDGE) == (DWORD)(m_sAppearance ?
       //      WS_EX_CLIENTEDGE : 0)));

       m_MyAppearance = nNewValue;
       SetModifiedFlag();

       //ToggleAppearance(this);
   // end of changes

       OnAppearanceChanged();

       BoundPropertyChanged(DISPID_APPEARANCE);
   }

   void CTestAppearanceCtrl::OnDraw(
               CDC* pdc, const CRect& rcBounds, const CRect& rcInvalid)
   {
       // TODO: Replace the following code with your own drawing code.
       pdc->FillRect(rcBounds,
            CBrush::FromHandle((HBRUSH)GetStockObject(WHITE_BRUSH)));
       pdc->Ellipse(rcBounds);

       // draw as 3D if m_appearance is set

       if(m_appearance)
       {
           CRect rect(rcBounds);
           pdc->DrawEdge(rect, EDGE_SUNKEN, BF_RECT | BF_ADJUST);
       }
   }