Containers Should Not Query for IOleInPlaceActiveObject

ID: Q98678

The information in this article applies to:

• Microsoft OLE Libraries for Windows and Win32s, version 2.0
• Microsoft OLE Libraries, included with:

      - Microsoft Windows NT, versions 3.5 and 3.51
      - Microsoft Windows 95
  

OLE (object linking and embedding) version 2.0 container applications should never call QueryInterface to get a pointer to the IOleInPlaceActiveObject interface. Instead, the container should AddRef() the pointer passed to IOleInPlaceUIWindow::SetActiveObject and save it until needed.

Consider the scenario in which a nested object is currently inplace active; that is, the container contains an object and this contained object in turn holds another object that is inplace active. The container has a pointer only to the "outer" object, and is not aware of the "inner" object. Calling QueryInterface to get a pointer to IOleInPlaceActiveObject is meaningless on the outer object because the outer object is not currently inplace active. The only reliable way to get a pointer to the correct IOleInPlaceActiveObject interface is through IOleInPlaceUIWindow::SetActiveObject.

Objects capable of inplace activation should guard against this case, and never return IOleInPlaceActiveObject from QueryInterface.

Additional reference words: 2.00 3.50 4.00 KBCategory: kbole kbprg KBSubcategory: LeTwoInp

Last Reviewed: May 17, 1995