Swift 4, 5
To pin a view to a safe area anchor using constraints can be done anywhere in the view controller's lifecycle because they're queued by the API and handled after the view has been loaded into memory. However, getting safe-area values requires waiting toward the end of a view controller's lifecycle, like viewDidLayoutSubviews().
This plugs into any view controller:
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
let topSafeArea: CGFloat
let bottomSafeArea: CGFloat
if #available(iOS 11.0, *) {
topSafeArea = view.safeAreaInsets.top
bottomSafeArea = view.safeAreaInsets.bottom
} else {
topSafeArea = topLayoutGuide.length
bottomSafeArea = bottomLayoutGuide.length
}
// safe area values are now available to use
}
I prefer this method to getting it off of the window (when possible) because it’s how the API was designed and, more importantly, the values are updated during all view changes, like device orientation changes.
However, some custom presented view controllers cannot use the above method (I suspect because they are in transient container views). In such cases, you can get the values off of the root view controller, which will always be available anywhere in the current view controller's lifecycle.
anyLifecycleMethod()
guard let root = UIApplication.shared.keyWindow?.rootViewController else {
return
}
let topSafeArea: CGFloat
let bottomSafeArea: CGFloat
if #available(iOS 11.0, *) {
topSafeArea = root.view.safeAreaInsets.top
bottomSafeArea = root.view.safeAreaInsets.bottom
} else {
topSafeArea = root.topLayoutGuide.length
bottomSafeArea = root.bottomLayoutGuide.length
}
// safe area values are now available to use
}