CXTPPropertyGridItem* CXTPPropertyGridView::InsertCategory(int nIndex, CString strCaption, CXTPPropertyGridItem* pCategory)
{
.....

   pCategory->m_nFlags = xtpGridItemHasExpandButton;
...
}
 

void CXTPPropertyGridPaintManager::DrawItem(PDRAWITEMSTRUCT lpDrawItemStruct)
{
....
   if (pItem->HasChilds() && pItem->GetFlags() & xtpGridItemHasExpandButton)
   {
      CRgn rgn;
      if (!pItem->IsCategory())
      {
         rgn.CreateRectRgnIndirect(&rcCaption);
         dc.SelectClipRgn(&rgn);
      }
      DrawExpandButton(dc, pItem, rcCaption);
      dc.SelectClipRgn(NULL);
    }
}
BOOL CXTPPropertyGridItem::OnLButtonDown(UINT, CPoint point)
{
....
   if(point.x >= nOffset && point.x <= XTP_PGI_EXPAND_BORDER + nOffset && m_nFlags & xtpGridItemHasExpandButton)
   {
      if(m_bExpanded) Collapse(); else Expand();
   }
AFX_INLINE void CXTPPropertyGridItem::SetFlags(UINT nFlags) {

// ASSERT(!m_bCategory);
ASSERT((nFlags & (xtpGridItemHasComboButton | xtpGridItemHasExpandButton)) != (xtpGridItemHasComboButton | xtpGridItemHasExpandButton));
m_nFlags = nFlags;
}