def METHOD_NAME(self, data_dir):
    if self.data_dir is not None:
        # remove old watch
        if self._watch is not None:
            self.observer.unschedule(self._watch)
    if data_dir is None or len(data_dir) == 0:
        self.data_dir = None
        return
    # add new watch folder
    event_handler = FileSystemEventHandler()
    event_handler.on_closed = self._file_detected_cb
    self._watch = self.observer.schedule(event_handler, data_dir,
                                         recursive=False)
    self.data_dir = data_dir