PRB: OLE Drop Target Does Not Permit Drop

MORE INFORMATION

Applications that register a window as an OLE drop target should probably check the position of a data object that is dragged over the window before permitting a drop to occur. For example, the MFC sample program Oclient performs the following check in its OnDragOver method:

   DROPEFFECT CMainView::OnDragOver(COleDataObject*,
      DWORD grfKeyState, CPoint point)
   {
      // adjust target rect by original cursor offset
      point -= m_dragOffset;

      // check for point outside logical area (in hatched region)
      // GetTotalSize() returns the size passed to SetScrollSizes
      CRect rectScroll(CPoint(0, 0), GetTotalSize());

      CRect rectItem(point,m_dragSize);
      rectItem.OffsetRect(GetDeviceScrollPosition());

      DROPEFFECT de = DROPEFFECT_NONE;
      CRect rectTemp;
      if (rectTemp.IntersectRect(rectScroll, rectItem))
      {
         //... figure out the drop effect
      }

      //...update drop effect

      return de;
   }
				

However, for some objects, such as Microsoft Word version 6.0 Documents, the m_dragSize reported by the data object is (0,0). In this case, the call to IntersectRect returns FALSE, and the drop effect returned is DROPEFFECT_NONE.

When the object position rectangle is inflated to size (1,1), IntersectRect returns TRUE and the correct drop effect is returned. In the previous example, you would inflate the rectangle by adding the following lines after the rectItem is declared:

   if (rectItem.IsRectEmpty())
   {
      // Some applications might have a null size in the object descriptor
      rectItem.InflateRect(1,1);
   }