About Common Control Notification Messages

Common controls are child windows that send notification messages to the parent window when events, such as input from the user, occur in the control. The application relies on these notification messages to determine what action the user wants it to take. Except for trackbars, which use WM_HSCROLL message, common controls send notification messages as WM_NOTIFY messages. The lParam parameter of WM_NOTIFY is either the address of an NMHDR structure or the address of a larger structure that includes NMHDR as its first member. The structure contains the notification code and identifies the common control that sent the notification message. The meaning of the remaining structure members, if any, varies depending on the notification code.

Each type of common control has a corresponding set of notification codes. The common control library also provides notification codes that can be sent by more than one type of common control. Values for common notification values are described in the following topics.