BCGSuite for MFC
BCGCBPRODLLEXPORT UINT BCGP_PLANNER_BEFORE_SELECT_APPOINTMENT

The message is sent to the parent of planner control before an appointment has been selected or unselected.

Parameters
wParamTRUE - the appointment is being selected. FALSE - the appointment will be unselected
lParama pointer to the appointment.
Returns
TRUE - cancel operation; FALSE - allow operation.