xscreensaver lock screen with Unity lock screen in Ubuntu 16.04

Question

I have searched many posts about "xscreensaver lock screen to use unity lock screen" such as: How do I configure xscreensaver to use the GNOME lockscreen on Ubuntu 14.04?
But I still don't know how to make it works.

I have removed the gnome-screensaver and there is no /usr/share/applications/gnome-screensaver.desktop. But there is one ~/.config/autostart/gnome-screensaver.desktop.

And I have add the xscreensaver entry into the "Startup Applications Preferences". Here is the xscreensaver setting:

And I have set the "Brightness & Lock" in setting panel:

And the final result is that the screensaver works, but it can't lock screen with the "unity lock screen".
And my system is Ubuntu 16.04 and the desktop environment is Unity (The output of echo $XDG_CURRENT_DESKTOP is Unity). (Though I don't know what is the difference between gnome and unity, I haven't change the desktop enviroment.) So how can I make the lock screen work with the Unity lock screen?

Thanks.