The HDN_BEGINTRACK notification message notifies a header control's parent window that the user has begun dragging a divider in the control (that is, the user has pressed the left mouse button while the mouse cursor is on a divider in the header control). This notification message is sent in the form of a WM_NOTIFY message.
HDN_BEGINTRACK
phdn = (HD_NOTIFY FAR *) lParam;
Parameters
phdn
Pointer to an HD_NOTIFY structure that contains information about the header control and the item whose divider is to be dragged.
Return Values
Returns FALSE to allow tracking of the divider or TRUE to prevent tracking.
See Also