def add_pre_action_callback(self, cb):
self._pre_action_callbacks.append(cb)<EOL>
Register a callback function to be invoked before each action (such as touch or swipe).

The callback function arguments are defined as follows:

* ``action`` (:obj:`str`): name or tag of the action
* ``proxy`` (:py:class:`UIObjectProxy <poco.proxy.UIObjectProxy>` or :obj:`NoneType`): related UI proxy which is
  involved in the action itself
* ``args`` (:obj:`tuple`): all required arguments of the specific action function

Args:
    cb: the callback function