Make UIScrollView fill parent view with constraints

Question

I am simply trying to add a scrollview in the view in Interface Builder and use constraints to have this scroll view fill its superview entirely

This is basically how it looks

Why - when I click on the trailing or leading constraints - is the constant set to -20 instead of 0?

Why - when I run the app and inspect the view - can I see that the view has a width of 375 (running on iPhone 6) but the scrollview has a width of 383?

Answer 1

Uncheck Constraint to margins when you setting constraint to your scrollview. By default it is checked and it constraints from margin.

check the screenshot below,