C / C++ / MFC

Example

// OnColorClicked() is a member function of CColorPage (a
// CPropertyPage-derived class). It is called whenever a radio button
// is selected on the page. Call SetModified() to enable the Apply 
// button whenever a new selection is made. m_Color is a member
// variable of CColorPage and it is to store the selected RGB color.

BEGIN_MESSAGE_MAP(CColorPage, CPropertyPage)
   ON_CONTROL_RANGE(BN_CLICKED, IDC_BLACK, IDC_BLUE, OnColorClicked)
   //{{AFX_MSG_MAP(CColorPage)
   //}}AFX_MSG_MAP
END_MESSAGE_MAP()

void CColorPage::OnColorClicked(UINT nCmdID)
{
   COLORREF color;
   switch (nCmdID)
   {
   case IDC_BLACK:
      color = RGB(0, 0, 0);
      break;

   case IDC_RED:
      color = RGB(255, 0, 0);
      break;

   case IDC_GREEN:
      color = RGB(0, 255, 0);
      break;

   case IDC_BLUE:
      color = RGB(0, 0, 255);
      break;
   }

   if (color != m_Color)
   {
      m_Color = color;
      SetModified();    //  Enable Apply Now button. <---
   }
}