def layers(self):
        """gets the service layers"""
        if self._layers is None:
            self.__init()
        lyrs = []
        for lyr in self._layers:
            url = self._url + "/%s" % lyr['id']
            lyr['object'] = MobileServiceLayer(url=url,
                                               securityHandler=self._securityHandler,
                                               proxy_url=self._proxy_url,
                                               proxy_port=self._proxy_port,
                                               initialize=False)
        return self._layers
gets the service layers