code: def get(cls):
          
          app = AndroidApplication.instance()
          f = app.create_future()
  
          if cls._instance:
              f.set_result(cls._instance)
              return f
  
          def on_service(obj_id):
              #: Create the manager
              if not cls.instance():
                  m = cls(__id__=obj_id)
              else:
                  m = cls.instance()
              f.set_result(m)
  
          cls.from_(app).then(on_service)
  
          return f
docs: Acquires the NotificationManager service async.