Event Constants

This topic describes the events that are generated by the operating system and by server applications. The constants are listed in alphabetical order.

Prior to using these events, client applications should use Accessible Event Watcher to verify that these events are used by UI elements.

For more information about events in general, see What Are WinEvents? and System Level and Object Level Events. For more information about the events sent by the system, see Appendix A: Supported User Interface Elements Reference.

Constant/valueDescription
EVENT_AIA_START / EVENT_AIA_END
0xA000-0xAFFF

The range of WinEvent constant values specified by the Accessibility Interoperability Alliance (AIA) for use across the industry. For more information, see Allocation of WinEvent IDs.

EVENT_MIN / EVENT_MAX
0x00000001-0x7FFFFFFF

The lowest and highest possible event values.

EVENT_OBJECT_ACCELERATORCHANGE
0x8012

An object's KeyboardShortcut property has changed. Server applications send this event for their accessible objects.

EVENT_OBJECT_CONTENTSCROLLED
0x8015

A window object's scrolling has ended. Unlike EVENT_SYSTEM_SCROLLEND, this event is associated with the scrolling window. Whether the scrolling is horizontal or vertical scrolling, this event should be sent whenever the scroll action is completed.

The hwnd parameter of the WinEventProc callback function describes the scrolling window; the idObject parameter is OBJID_CLIENT, and the idChild parameter is CHILDID_SELF.

EVENT_OBJECT_CREATE
0x8000

An object has been created. The system sends this event for the following user interface elements: caret, header control, list-view control, tab control, toolbar control, tree view control, and window object. Server applications send this event for their accessible objects.

Before sending the event for the parent object, servers must send it for all of an object's child objects. Servers must ensure that all child objects are fully created and ready to accept IAccessible calls from clients before the parent object sends this event.

Because a parent object is created after its child objects, clients must make sure that an object's parent has been created before calling IAccessible::get_accParent, particularly if in-context hook functions are used.

EVENT_OBJECT_DEFACTIONCHANGE
0x8011

An object's DefaultAction property has changed. The system sends this event for dialog boxes. Server applications send this event for their accessible objects.

EVENT_OBJECT_DESCRIPTIONCHANGE
0x800D

An object's Description property has changed. Server applications send this event for their accessible objects.

EVENT_OBJECT_DESTROY
0x8001

An object has been destroyed. The system sends this event for the following user interface elements: caret, header control, list-view control, tab control, toolbar control, tree view control, and window object. Server applications send this event for their accessible objects.

Clients assume that all of an object's children are destroyed when the parent object sends this event.

After receiving this event, clients do not call an object's IAccessible properties or methods. However, the interface pointer must remain valid as long as there is a reference count on it (due to COM rules), but the UI element may no longer be present. Further calls on the interface pointer may return failure errors; to prevent this, servers create proxy objects and monitor their life spans.

EVENT_OBJECT_DRAGSTART
0x8021

The user started to drag an element. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the object being dragged.

EVENT_OBJECT_DRAGCANCEL
0x8022

The user has ended a drag operation before dropping the dragged element on a drop target. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the object being dragged.

EVENT_OBJECT_DRAGCOMPLETE
0x8023

The user dropped an element on a drop target. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the object being dragged.

EVENT_OBJECT_DRAGENTER
0x8024

The user dragged an element into a drop target's boundary. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the drop target.

EVENT_OBJECT_DRAGLEAVE
0x8025

The user dragged an element out of a drop target's boundary. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the drop target.

EVENT_OBJECT_DRAGDROPPED
0x8026

The user dropped an element on a drop target. The hwnd, idObject, and idChild parameters of the WinEventProc callback function identify the drop target.

EVENT_OBJECT_END
0x80FF

The highest object event value.

EVENT_OBJECT_FOCUS
0x8005

An object has received the keyboard focus. The system sends this event for the following user interface elements: list-view control, menu bar, pop-up menu, switch window, tab control, tree view control, and window object. Server applications send this event for their accessible objects.

The hwnd parameter of the WinEventProc callback function identifies the window that receives the keyboard focus.

EVENT_OBJECT_HELPCHANGE
0x8010

An object's Help property has changed. Server applications send this event for their accessible objects.

EVENT_OBJECT_HIDE
0x8003

An object is hidden. The system sends this event for the following user interface elements: caret and cursor. Server applications send this event for their accessible objects.

When this event is generated for a parent object, all child objects are already hidden. Server applications do not send this event for the child objects.

Hidden objects include the STATE_SYSTEM_INVISIBLE flag; shown objects do not include this flag. The EVENT_OBJECT_HIDE event also indicates that the STATE_SYSTEM_INVISIBLE flag is set. Therefore, servers do not send the EVENT_STATE_CHANGE event in this case.

EVENT_OBJECT_HOSTEDOBJECTSINVALIDATED
0x8020

A window that hosts other accessible objects has changed the hosted objects. A client might need to query the host window to discover the new hosted objects, especially if the client has been monitoring events from the window. A hosted object is an object from an accessibility framework (MSAA or UI Automation) that is different from that of the host. Changes in hosted objects that are from the same framework as the host should be handed with the structural change events, such as EVENT_OBJECT_CREATE for MSAA. For more info see comments within winuser.h.

EVENT_OBJECT_IME_HIDE
0x8028

An IME window has become hidden.

EVENT_OBJECT_IME_SHOW
0x8027

An IME window has become visible.

EVENT_OBJECT_IME_CHANGE
0x8029

The size or position of an IME window has changed.

EVENT_OBJECT_INVOKED
0x8013

An object has been invoked; for example, the user has clicked a button. This event is supported by common controls and is used by UI Automation.

For this event, the hwnd, ID, and idChild parameters of the WinEventProc callback function identify the item that is invoked.

EVENT_OBJECT_LIVEREGIONCHANGED
0x8019

An object that is part of a live region has changed. A live region is an area of an application that changes frequently and/or asynchronously.

EVENT_OBJECT_LOCATIONCHANGE
0x800B

An object has changed location, shape, or size. The system sends this event for the following user interface elements: caret and window objects. Server applications send this event for their accessible objects.

This event is generated in response to a change in the top-level object within the object hierarchy; it is not generated for any children that the object might have. For example, if the user resizes a window, the system sends this notification for the window, but not for the menu bar, title bar, scroll bar, or other objects that have also changed.

The system does not send this event for every non-floating child window when the parent moves. However, if an application explicitly resizes child windows as a result of resizing the parent window, the system sends multiple events for the resized children.

If an object's State property is set to STATE_SYSTEM_FLOATING, the server sends EVENT_OBJECT_LOCATIONCHANGE whenever the object changes location. If an object does not have this state, servers only trigger this event when the object moves in relation to its parent. For this event notification, the idChild parameter of the WinEventProc callback function identifies the child object that has changed.

EVENT_OBJECT_NAMECHANGE
0x800C

An object's Name property has changed. The system sends this event for the following user interface elements: check box, cursor, list-view control, push button, radio button, status bar control, tree view control, and window object. Server applications send this event for their accessible objects.

EVENT_OBJECT_PARENTCHANGE
0x800F

An object has a new parent object. Server applications send this event for their accessible objects.

EVENT_OBJECT_REORDER
0x8004

A container object has added, removed, or reordered its children. The system sends this event for the following user interface elements: header control, list-view control, toolbar control, and window object. Server applications send this event as appropriate for their accessible objects.

For example, this event is generated by a list-view object when the number of child elements or the order of the elements changes. This event is also sent by a parent window when the Z-order for the child windows changes.

EVENT_OBJECT_SELECTION
0x8006

The selection within a container object has changed. The system sends this event for the following user interface elements: list-view control, tab control, tree view control, and window object. Server applications send this event for their accessible objects.

This event signals a single selection: either a child is selected in a container that previously did not contain any selected children, or the selection has changed from one child to another.

The hwnd and idObject parameters of the WinEventProc callback function describe the container; the idChild parameter identifies the object that is selected. If the selected child is a window that also contains objects, the idChild parameter is OBJID_WINDOW.

EVENT_OBJECT_SELECTIONADD
0x8007

A child within a container object has been added to an existing selection. The system sends this event for the following user interface elements: list box, list-view control, and tree view control. Server applications send this event for their accessible objects.

The hwnd and idObject parameters of the WinEventProc callback function describe the container. The idChild parameter is the child that is added to the selection.

EVENT_OBJECT_SELECTIONREMOVE
0x8008

An item within a container object has been removed from the selection. The system sends this event for the following user interface elements: list box, list-view control, and tree view control. Server applications send this event for their accessible objects.

This event signals that a child is removed from an existing selection.

The hwnd and idObject parameters of the WinEventProc callback function describe the container; the idChild parameter identifies the child that has been removed from the selection.

EVENT_OBJECT_SELECTIONWITHIN
0x8009

Numerous selection changes have occurred within a container object. The system sends this event for list boxes; server applications send it for their accessible objects.

This event is sent when the selected items within a control have changed substantially. The event informs the client that many selection changes have occurred, and it is sent instead of several EVENT_OBJECT_SELECTIONADD or EVENT_OBJECT_SELECTIONREMOVE events. The client queries for the selected items by calling the container object's IAccessible::get_accSelection method and enumerating the selected items.

For this event notification, the hwnd and idObject parameters of the WinEventProc callback function describe the container in which the changes occurred.

EVENT_OBJECT_SHOW
0x8002

A hidden object is shown. The system sends this event for the following user interface elements: caret, cursor, and window object. Server applications send this event for their accessible objects.

Clients assume that when this event is sent by a parent object, all child objects are already displayed. Therefore, server applications do not send this event for the child objects.

Hidden objects include the STATE_SYSTEM_INVISIBLE flag; shown objects do not include this flag. The EVENT_OBJECT_SHOW event also indicates that the STATE_SYSTEM_INVISIBLE flag is cleared. Therefore, servers do not send the EVENT_STATE_CHANGE event in this case.

EVENT_OBJECT_STATECHANGE
0x800A

An object's state has changed. The system sends this event for the following user interface elements: check box, combo box, header control, push button, radio button, scroll bar, toolbar control, tree view control, up-down control, and window object. Server applications send this event for their accessible objects.

For example, a state change occurs when a button object is clicked or released, or when an object is enabled or disabled.

For this event notification, the idChild parameter of the WinEventProc callback function identifies the child object whose state has changed.

EVENT_OBJECT_TEXTEDIT_CONVERSIONTARGETCHANGED
0x8030

The conversion target within an IME composition has changed. The conversion target is the subset of the IME composition which is actively selected as the target for user-initiated conversions.

EVENT_OBJECT_TEXTSELECTIONCHANGED
0x8014

An object's text selection has changed. This event is supported by common controls and is used by UI Automation.

The hwnd, ID, and idChild parameters of the WinEventProc callback function describe the item that is contained in the updated text selection.

EVENT_OBJECT_VALUECHANGE
0x800E

An object's Value property has changed. The system sends this event for the user interface elements that include the scroll bar and the following controls: edit, header, hot key, progress bar, slider, and up-down. Server applications send this event for their accessible objects.

EVENT_OEM_DEFINED_START / EVENT_OEM_DEFINED_END
0x0101-0x01FF

The range of event constant values reserved for OEMs. For more information, see Allocation of WinEvent IDs.

EVENT_SYSTEM_ALERT
0x0002

An alert has been generated. Server applications should not send this event.

EVENT_SYSTEM_ARRANGMENTPREVIEW
0x8016

A preview rectangle is being displayed.

EVENT_SYSTEM_CAPTUREEND
0x0009

A window has lost mouse capture. This event is sent by the system, never by servers.

EVENT_SYSTEM_CAPTURESTART
0x0008

A window has received mouse capture. This event is sent by the system, never by servers.

EVENT_SYSTEM_CONTEXTHELPEND
0x000D

A window has exited context-sensitive Help mode. This event is not sent consistently by the system.

EVENT_SYSTEM_CONTEXTHELPSTART
0x000C

A window has entered context-sensitive Help mode. This event is not sent consistently by the system.

EVENT_SYSTEM_DESKTOPSWITCH
0x0020

The active desktop has been switched.

EVENT_SYSTEM_DIALOGEND
0x0011

A dialog box has been closed. The system sends this event for standard dialog boxes; servers send it for custom dialog boxes. This event is not sent consistently by the system.

EVENT_SYSTEM_DIALOGSTART
0x0010

A dialog box has been displayed. The system sends this event for standard dialog boxes, which are created using resource templates or Win32 dialog box functions. Servers send this event for custom dialog boxes, which are windows that function as dialog boxes but are not created in the standard way.

This event is not sent consistently by the system.

EVENT_SYSTEM_DRAGDROPEND
0x000F

An application is about to exit drag-and-drop mode. Applications that support drag-and-drop operations must send this event; the system does not send this event.

EVENT_SYSTEM_DRAGDROPSTART
0x000E

An application is about to enter drag-and-drop mode. Applications that support drag-and-drop operations must send this event because the system does not send it.

EVENT_SYSTEM_END
0x00FF

The highest system event value.

EVENT_SYSTEM_FOREGROUND
0x0003

The foreground window has changed. The system sends this event even if the foreground window has changed to another window in the same thread. Server applications never send this event.

For this event, the WinEventProc callback function's hwnd parameter is the handle to the window that is in the foreground, the idObject parameter is OBJID_WINDOW, and the idChild parameter is CHILDID_SELF.

EVENT_SYSTEM_MENUPOPUPEND
0x0007

A pop-up menu has been closed. The system sends this event for standard menus; servers send it for custom menus.

When a pop-up menu is closed, the client receives this message, and then the EVENT_SYSTEM_MENUEND event.

This event is not sent consistently by the system.

EVENT_SYSTEM_MENUPOPUPSTART
0x0006

A pop-up menu has been displayed. The system sends this event for standard menus, which are identified by HMENU, and are created using menu-template resources or Win32 menu functions. Servers send this event for custom menus, which are user interface elements that function as menus but are not created in the standard way. This event is not sent consistently by the system.

EVENT_SYSTEM_MENUEND
0x0005

A menu from the menu bar has been closed. The system sends this event for standard menus; servers send it for custom menus.

For this event, the WinEventProc callback function's hwnd, idObject, and idChild parameters refer to the control that contains the menu bar or the control that activates the context menu. The hwnd parameter is the handle to the window that is related to the event. The idObject parameter is OBJID_MENU or OBJID_SYSMENU for a menu, or OBJID_WINDOW for a pop-up menu. The idChild parameter is CHILDID_SELF.

EVENT_SYSTEM_MENUSTART
0x0004

A menu item on the menu bar has been selected. The system sends this event for standard menus, which are identified by HMENU, created using menu-template resources or Win32 menu API elements. Servers send this event for custom menus, which are user interface elements that function as menus but are not created in the standard way.

For this event, the WinEventProc callback function's hwnd, idObject, and idChild parameters refer to the control that contains the menu bar or the control that activates the context menu. The hwnd parameter is the handle to the window related to the event. The idObject parameter is OBJID_MENU or OBJID_SYSMENU for a menu, or OBJID_WINDOW for a pop-up menu. The idChild parameter is CHILDID_SELF.

The system triggers more than one EVENT_SYSTEM_MENUSTART event that does not always correspond with the EVENT_SYSTEM_MENUEND event.

EVENT_SYSTEM_MINIMIZEEND
0x0017

A window object is about to be restored. This event is sent by the system, never by servers.

EVENT_SYSTEM_MINIMIZESTART
0x0016

A window object is about to be minimized. This event is sent by the system, never by servers.

EVENT_SYSTEM_MOVESIZEEND
0x000B

The movement or resizing of a window has finished. This event is sent by the system, never by servers.

EVENT_SYSTEM_MOVESIZESTART
0x000A

A window is being moved or resized. This event is sent by the system, never by servers.

EVENT_SYSTEM_SCROLLINGEND
0x0013

Scrolling has ended on a scroll bar. This event is sent by the system for standard scroll bar controls and for scroll bars that are attached to a window. Servers send this event for custom scroll bars, which are user interface elements that function as scroll bars but are not created in the standard way.

The idObject parameter that is sent to the WinEventProc callback function is OBJID_HSCROLL for horizontal scroll bars, and OBJID_VSCROLL for vertical scroll bars.

EVENT_SYSTEM_SCROLLINGSTART
0x0012

Scrolling has started on a scroll bar. The system sends this event for standard scroll bar controls and for scroll bars attached to a window. Servers send this event for custom scroll bars, which are user interface elements that function as scroll bars but are not created in the standard way.

The idObject parameter that is sent to the WinEventProc callback function is OBJID_HSCROLL for horizontal scrolls bars, and OBJID_VSCROLL for vertical scroll bars.

EVENT_SYSTEM_SOUND
0x0001

A sound has been played. The system sends this event when a system sound, such as one for a menu, is played even if no sound is audible (for example, due to the lack of a sound file or a sound card). Servers send this event whenever a custom UI element generates a sound.

For this event, the WinEventProc callback function receives the OBJID_SOUND value as the idObject parameter.

EVENT_SYSTEM_SWITCHEND
0x0015

The user has released ALT+TAB. This event is sent by the system, never by servers. The hwnd parameter of the WinEventProc callback function identifies the window to which the user has switched.

If only one application is running when the user presses ALT+TAB, the system sends this event without a corresponding EVENT_SYSTEM_SWITCHSTART event.

EVENT_SYSTEM_SWITCHSTART
0x0014

The user has pressed ALT+TAB, which activates the switch window. This event is sent by the system, never by servers. The hwnd parameter of the WinEventProc callback function identifies the window to which the user is switching.

If only one application is running when the user presses ALT+TAB, the system sends an EVENT_SYSTEM_SWITCHEND event without a corresponding EVENT_SYSTEM_SWITCHSTART event.

EVENT_UIA_EVENTID_START / EVENT_UIA_EVENTID_END
0x4E00-0x4EFF

The range of event constant values reserved for UI Automation event identifiers. For more information, see Allocation of WinEvent IDs.

EVENT_UIA_PROPID_START / EVENT_UIA_PROPID_END
0x7500-0x75FF

The range of event constant values reserved for UI Automation property-changed event identifiers. For more information, see Allocation of WinEvent IDs.

Requirements

Header

Winuser.h (include Windows.h)

 

 

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