Object Identifiers

Object Identifiers

This topic describes the Microsoft Active Accessibility object identifiers, 32-bit values that identify categories of accessible objects within a window. Microsoft Active Accessibility servers and Microsoft UI Automation providers use the object identifiers to determine the object to which a WM_GETOBJECT message request refers.

Clients receive these values in their WinEventProc callback function and use them to identify parts of a window. Servers use these values to identify the corresponding parts of a window when calling NotifyWinEvent or when responding to the WM_GETOBJECT message.

Servers can define custom object IDs to identify other categories of objects within their applications. Custom object IDs must be assigned positive values because Microsoft Active Accessibility reserves zero and all negative values for the following standard object identifiers.

The following constants are defined in winuser.h:


An alert that is associated with a window or an application. System provided message boxes are the only UI elements that send events with this object identifier. Server applications cannot use the AccessibleObjectFromX functions with this object identifier. This is a known issue with Microsoft Active Accessibility.


The text insertion bar (caret) in the window.


The window's client area. In most cases, the operating system controls the frame elements and the client object contains all elements that are controlled by the application. Servers only process the WM_GETOBJECT messages in which the lParam is OBJID_CLIENT, OBJID_WINDOW, or a custom object identifier.


The mouse pointer. There is only one mouse pointer in the system, and it is not a child of any window.


The window's horizontal scroll bar.


In response to this object identifier, third-party applications can expose their own object model. Third-party applications can return any COM interface in response to this object identifier.


The window's menu bar.


An object identifier that Oleacc.dll uses internally. For more information, see Appendix F: Object Identifier Values for OBJID_QUERYCLASSNAMEIDX.


The window's size grip: an optional frame component located at the lower-right corner of the window frame.


A sound object. Sound objects do not have screen locations or children, but they do have name and state attributes. They are children of the application that is playing the sound.


The window's system menu.


The window's title bar.


The window's vertical scroll bar.


The window itself rather than a child object.



Winuser.h (include Windows.h)



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