BCGControlBar Pro for MFC
virtual void CBCGPGridCtrl::OnHideColumnChooser ( )

Called by the framework when the column chooser has been hidden. The column chooser is a popup window that contains a list of hidden columns, displayed as buttons with column names. The user can drag buttons from the column chooser and drop them on the grid header. The dropped columns will appear on the grid header. Override this function if you need custom processing on this event. The default implementation sends the BCGM_GRID_ON_HIDE_COLUMNCHOOSER notification message to the grid's owner.