Use OBJID_NATIVEOM to expose a native interface for a window

This technique allows clients to get a custom object for a window. Servers can use this to expose a pointer to a custom document object for a window.

To expose a native object model interface for a window (servers)

1. Handle the WM_GETOBJECT message in the window procedure. When the lParam value is OBJID_NATIVEOM, return an interface pointer to the custom object using LresultFromObject.
2. Release your interface pointer after calling LresultFromObject, if appropriate. For more information, see LresultFromObject.

Clients can obtain a pointer to this custom object.

To obtain a pointer for a custom object for a window (clients)

• Call AccessibleObjectFromWindow and pass OBJID_NATIVEOM as the second parameter.

Note the following issues for this technique:

• This technique is similar to returning an IAccessible interface pointer except for the object ID used and the fact that LresultFromObject returns a custom object instead of IAccessible.
• Server developers may need to publish information that allows clients to uniquely identify the HWND so that they can find it before calling AccessibleObjectFromWindow on its window handle.
• Do not implement the IAccessible interface on the custom object that is returned. If you do, OLEACC will treat it is as a standard IAccessible and may prevent the custom interfaces from being used.
• In order to be used across processes, the interfaces on the returned object may need to be registered with Component Object Model (COM).

This technique is supported by several Microsoft Office components. For more information, see AccessibleObjectFromWindow.