def METHOD_NAME(self, freq):
    self._current_frequency = freq
    if self._lx is None:
        self._lx = self._axes.axvline(linewidth=2, color="red")
    self._lx.set_xdata(self._current_frequency)
    # if self._fig.canvas.supports_blit:
    #     self._axes.draw_artist(self._lx)
    #     self._fig.canvas.blit(self._axes.bbox)
    # else:
    #     self._fig.canvas.draw_idle()
    self._fig.canvas.draw_idle()