I try to add schedule activity in form view.But , when I click SCHEDULE button in mail activity wizard form, not displayed in chatter. But when I click  MARK  AS  DONE  or  DONE  &  SCHEDULE  NEXT  button,  displayed  in  chatter.  Here is my code.

class MyMixedInCalendar(models.Model):
_name = 'calendar.event'
_inherit = ['calendar.event','\mail.activity.mixin','mail.thread']

full_name = fields.Char()