What is _UILayoutGuide?

Question

I need to know about _UILayoutGuide, like what it is, what it does and why it present in the hierarchy of UIView as a subview with alm

Answer 1

UILayoutGuide is normally referred to -topLayoutGuide and -bottomLayoutGuide, those are not really constraints, but they are view elements conform to a protocol called UILayoutSupport.

You can find more info about that protocol here. The value is often 0 but you should pay a lot of attention where you ask their size.