About Header Control Notification Messages
A header control sends notification messages to its parent window when the user clicks or double-clicks an item, when the user drags an item divider, and when the attributes of an item change. The parent window receives the notifications in the form of WM_NOTIFY messages. The following notifications are used with header controls.
| Notification | Description |
| HDN_BEGINTRACK | Signals the start of divider dragging. |
| HDN_DIVIDERDBLCLICK | Indicates that the user double-clicked a divider. |
| HDN_ENDTRACK | Signals the end of divider dragging. |
| HDN_ITEMCHANGED | Indicates a change in the attributes of an item. |
| HDN_ITEMCHANGING | Indicates that the attributes of an item are about to change. |
| HDN_ITEMCLICK | Indicates that the user clicked an item. |
| HDN_ITEMDBLCLICK | Indicates that the user double-clicked an item. |
| HDN_TRACK | Indicates that the user dragged a divider. |