BCGControlBar Pro for MFC
UINT BCGM_ON_BEFORE_RIBBON_BACKSTAGE_VIEW

Sent to Ribbon's parent before backstage view has been displayed.

Parameters
wParamthis parameter is not used.
lParamthis parameter is not used.
Returns
returns FALSE to display the backstage view. Returns TRUE to prevent the backstage view from being displayed.

The framework sends BCGM_ON_BEFORE_RIBBON_BACKSTAGE_VIEW registered message to the Ribbon's parent before backstage view has been displayed.