iOS 9 Safe Area Top constraint of xib and storyboard is different

Question

on iOS 9, iPhone 5, not happend on iOS 10 and later

UIViewController create from storyboard, I set the viewController's red subView's view.top equals to safe area top, the red view is just below the statusBar.

If create viewController from xib file, use init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) and also set red subView's view.top equals to safe area top, the red view is at same origin.y with the statusBar. Just as below:

The viewControllers create from storyboard and xib are the same class, maybe create from storyboard and xib have some different setting, I try to unselect all storyboard select option, but have not found the one that make the difference.

Can any one explain this? Thanks!

Repo for this question: https://github.com/codingingBoy/SafeAreaDemo.

Answer 1

There are backward compatibility issues with XIBs and Safe-Area guides with older iOS versions, because the XIB files did not have them.

In the current Xib backwards deployment behavior (iOS 10 and prior), a constraint to the safe area will be converted to the superview, because a XIB does not have top and bottom layout guides.

This may not achieve the layout behavior that you want, and we recommend you working around this case with one of the following options:

1) move the the view and layout to a storyboard view controller

2) use IB Outlets to the relevant (top and bottom) constraints, and programatically replace them with constraints to top/bottom layout guide once the view gets installed

3) install the view as a subview, and programmatically add constraints to top/bottom layout guides and sides.

Ref: https://forums.developer.apple.com/thread/87329