In your plan, you must learn the word 10 or more. (pro-test. Otherwise, the lock screen is five words, which can't be displayed at all)

Android phone system lock screen must be turned off. These two kinds of lock screens seem to conflict. You can try more yourself.

You can't close this application in the background of your mobile phone. Before, my dictionary was inexplicably closed in the background, so the lock screen kept disappearing.

The above is my answer, I hope it will help you.