Object identifiers are 32-bit values that identify categories of accessible objects within an application.
Clients receive these values in their WinEventProc callback function and use them to identify parts of a window. Servers also 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 to use for the following standard object identifiers.
The following constants are defined in winuser.h:
- Refers to an alert associated with a window or an application. System provided message boxes are the only UI elements that send events with this ID. Server applications cannot use the AccessibleObjectFromX functions with this object identifier. This is a known issue with Active Accessibility.
- Refers to the text insertion bar (caret) in the window.
- Refers to the window's client area. In most cases, the operating system controls the frame elements and the client object contains all elements that the application controls. When processing the WM_GETOBJECT message, servers only process the messages in which the lParam is OBJID_CLIENT, OBJID_WINDOW, or custom object IDs.
- Refers to the mouse pointer. There is only one mouse pointer in the system and it is not a child of any window.
- Refers to 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.
- Refers to the window's menu bar.
- Refers to an object identifier that OLEACC.dll uses internally. For more information, see Appendix F: Object Identifier Values for OBJID_QUERYCLASSNAMEIDX.
- Refers to the window's size grip, an optional frame component located at the lower right corner of the window frame.
- Refers to a sound object. Sound objects do not have screen locations or children, but do have name and state attributes. They are children of the application playing the sound.
- Refers to the window's system menu.
- Refers to the window's title bar.
- Refers to the window's vertical scroll bar.
- Refers to the window itself rather than a child object.