Questions about freeScreen and unFreezeScreen

In the process of which this sentence

[[UIApplication sharedApplication] delegate freezeScreen.];
.......
[[UIApplication sharedApplication] delegate unFreezeScreen.];

Which freezeScreen and unFreezeScreen function

Compile time here warn display
-FreezeScreen not found in protocol (s)
-No 'unFreeScreen' method found
message without a mathing method signature will be assumed to return 'id' and accept '...' as arguments

At the same time I did not find explanation
about these two methods in the document
But these two words does play a role, lock screen and unlock screen

This is how it