Windows Message Notifications

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WM_ACTIVATEAPP

The WM_ACTIVATEAPP message is sent when a window belonging to a different application than the active window is about to be activated. The message is sent to the application whose window is being activated and to the application whose window is being deactivated.

A window receives this message through its WindowProc function.

WM_CANCELMODE

The WM_CANCELMODE message is sent to cancel certain modes, such as mouse capture. For example, the system sends this message to the active window when a dialog box or message box is displayed. Certain functions also send this message explicitly to the specified window regardless of whether it is the active window. For example, the EnableWindow function sends this message when disabling the specified window.

A window receives this message through its WindowProc function.

WM_CHILDACTIVATE

The WM_CHILDACTIVATE message is sent to a child window when the user clicks the window's title bar or when the window is activated, moved, or sized.

A window receives this message through its WindowProc function.

WM_CLOSE

The WM_CLOSE message is sent as a signal that a window or an application should terminate.

A window receives this message through its WindowProc function.

WM_COMPACTING

The WM_COMPACTING message is sent to all top-level windows when the system detects more than 12.5 percent of system time over a 30- to 60-second interval is being spent compacting memory. This indicates that system memory is low.

A window receives this message through its WindowProc function.

Note  This message is provided only for compatibility with 16-bit Windows-based applications.

WM_CREATE

The WM_CREATE message is sent when an application requests that a window be created by calling the CreateWindowEx or CreateWindow function. (The message is sent before the function returns.) The window procedure of the new window receives this message after the window is created, but before the window becomes visible.

A window receives this message through its WindowProc function.

WM_DESTROY

The WM_DESTROY message is sent when a window is being destroyed. It is sent to the window procedure of the window being destroyed after the window is removed from the screen.

This message is sent first to the window being destroyed and then to the child windows (if any) as they are destroyed. During the processing of the message, it can be assumed that all child windows still exist.

A window receives this message through its WindowProc function.

WM_ENABLE

The WM_ENABLE message is sent when an application changes the enabled state of a window. It is sent to the window whose enabled state is changing. This message is sent before the EnableWindow function returns, but after the enabled state (WS_DISABLED style bit) of the window has changed.

A window receives this message through its WindowProc function.

WM_ENTERSIZEMOVE

The WM_ENTERSIZEMOVE message is sent one time to a window after it enters the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

The system sends the WM_ENTERSIZEMOVE message regardless of whether the dragging of full windows is enabled.

A window receives this message through its WindowProc function.

WM_EXITSIZEMOVE

The WM_EXITSIZEMOVE message is sent one time to a window, after it has exited the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

A window receives this message through its WindowProc function.

WM_GETICON

The WM_GETICON message is sent to a window to retrieve a handle to the large or small icon associated with a window. The system displays the large icon in the ALT+TAB dialog, and the small icon in the window caption.

A window receives this message through its WindowProc function.

WM_GETMINMAXINFO

The WM_GETMINMAXINFO message is sent to a window when the size or position of the window is about to change. An application can use this message to override the window's default maximized size and position, or its default minimum or maximum tracking size.

A window receives this message through its WindowProc function.

WM_INPUTLANGCHANGE

The WM_INPUTLANGCHANGE message is sent to the topmost affected window after an application's input language has been changed. You should make any application-specific settings and pass the message to the DefWindowProc function, which passes the message to all first-level child windows. These child windows can pass the message to DefWindowProc to have it pass the message to their child windows, and so on.

A window receives this message through its WindowProc function.

WM_INPUTLANGCHANGEREQUEST

The WM_INPUTLANGCHANGEREQUEST message is posted to the window with the focus when the user chooses a new input language, either with the hotkey (specified in the Keyboard control panel application) or from the indicator on the system taskbar. An application can accept the change by passing the message to the DefWindowProc function or reject the change (and prevent it from taking place) by returning immediately.

A window receives this message through its WindowProc function.

WM_MOVE

The WM_MOVE message is sent after a window has been moved.

A window receives this message through its WindowProc function.

WM_MOVING

The WM_MOVING message is sent to a window that the user is moving. By processing this message, an application can monitor the position of the drag rectangle and, if needed, change its position.

A window receives this message through its WindowProc function.

WM_NCACTIVATE

The WM_NCACTIVATE message is sent to a window when its nonclient area needs to be changed to indicate an active or inactive state.

A window receives this message through its WindowProc function.

WM_NCCALCSIZE

The WM_NCCALCSIZE message is sent when the size and position of a window's client area must be calculated. By processing this message, an application can control the content of the window's client area when the size or position of the window changes.

A window receives this message through its WindowProc function.

WM_NCCREATE

The WM_NCCREATE message is sent prior to the WM_CREATE message when a window is first created.

A window receives this message through its WindowProc function.

WM_NCDESTROY

The WM_NCDESTROY message informs a window that its nonclient area is being destroyed. The DestroyWindow function sends the WM_NCDESTROY message to the window following the WM_DESTROY message. WM_DESTROY is used to free the allocated memory object associated with the window.

The WM_NCDESTROY message is sent after the child windows have been destroyed. In contrast, WM_DESTROY is sent before the child windows are destroyed.

A window receives this message through its WindowProc function.

WM_NULL

The WM_NULL message performs no operation. An application sends the WM_NULL message if it wants to post a message that the recipient window will ignore.

A window receives this message through its WindowProc function.

WM_PARENTNOTIFY

The WM_PARENTNOTIFY message is sent to the parent of a child window when the child window is created or destroyed, or when the user clicks a mouse button while the cursor is over the child window. When the child window is being created, the system sends WM_PARENTNOTIFY just before the CreateWindow or CreateWindowEx function that creates the window returns. When the child window is being destroyed, the system sends the message before any processing to destroy the window takes place.

A window receives this message through its WindowProc function.

WM_QUERYDRAGICON

The WM_QUERYDRAGICON message is sent to a minimized (iconic) window. The window is about to be dragged by the user but does not have an icon defined for its class. An application can return a handle to an icon or cursor. The system displays this cursor or icon while the user drags the icon.

A window receives this message through its WindowProc function.

WM_QUERYOPEN

The WM_QUERYOPEN message is sent to an icon when the user requests that the window be restored to its previous size and position.

A window receives this message through its WindowProc function.

WM_SHOWWINDOW

The WM_SHOWWINDOW message is sent to a window when the window is about to be hidden or shown.

A window receives this message through its WindowProc function.

WM_SIZE

The WM_SIZE message is sent to a window after its size has changed.

A window receives this message through its WindowProc function.

WM_SIZING

The WM_SIZING message is sent to a window that the user is resizing. By processing this message, an application can monitor the size and position of the drag rectangle and, if needed, change its size or position.

A window receives this message through its WindowProc function.

WM_STYLECHANGED

The WM_STYLECHANGED message is sent to a window after the SetWindowLong function has changed one or more of the window's styles.

A window receives this message through its WindowProc function.

WM_STYLECHANGING

The WM_STYLECHANGING message is sent to a window when the SetWindowLong function is about to change one or more of the window's styles.

A window receives this message through its WindowProc function.

WM_THEMECHANGED

The WM_THEMECHANGED message is broadcast to every window following a theme change event. Examples of theme change events are the activation of a theme, the deactivation of a theme, or a transition from one theme to another.

WM_USERCHANGED

The WM_USERCHANGED message is sent to all windows after the user has logged on or off. When the user logs on or off, the system updates the user-specific settings. The system sends this message immediately after updating the settings.

A window receives this message through its WindowProc function.

WM_WINDOWPOSCHANGED

The WM_WINDOWPOSCHANGED message is sent to a window whose size, position, or place in the Z order has changed as a result of a call to the SetWindowPos function or another window-management function.

A window receives this message through its WindowProc function.

WM_WINDOWPOSCHANGING

The WM_WINDOWPOSCHANGING message is sent to a window whose size, position, or place in the Z order is about to change as a result of a call to the SetWindowPos function or another window-management function.

A window receives this message through its WindowProc function.