iOS 11 Extra Space on NavigationBar - swift

Question

I changed my searchBar code from:
self.navigationItem.titleView = searchNavigation.searchController.searchBar;
to:
if (#available(iOS 11.0, *)) {
self.navigationItem.searchController = searchNavigation.searchController;
self.navigationController.navigationBar.prefersLargeTitles = NO;
self.navigationItem.largeTitleDisplayMode = UINavigationItemLargeTitleDisplayModeNever;
} else {
self.navigationItem.titleView = searchNavigation.searchController.searchBar;
}
but when try on ios 11 it looks like
there is extra space over searchBar and when i start to typing its slide top top and looks normal

Answer 1

First for iOS 11 you are assigning your search controller to the navigation items searchController properties instead of as it's titleView. If you do that then the search bar appears below the navigation bar as you have seen.
Second there is a property on the UISearchController called hidesNavigationBarDuringPresentation which controls whether the search bar moves up to hide the navigation bar when in use.
To replicate for iOS 11 what you have for previous versions do this instead:
if (#available(iOS 11.0, *)) {
self.navigationItem.titleView =
searchNavigation.searchController.searchBar;
searchNavigation.searchController.hidesNavigationBarDuringPresentation = NO;
self.navigationController.navigationBar.prefersLargeTitles = NO;
self.navigationItem.largeTitleDisplayMode = UINavigationItemLargeTitleDisplayModeNever;
} else {
self.navigationItem.titleView =
searchNavigation.searchController.searchBar;
}

Answer 2

As previous answers have mentioned, setting the navigation bar's searchController as the desired search bar will produce the search bar sitting below the navigation bar's new "large title".
To stop this new behaviour you need to override the navigation bar's titleView with the search bar itself and disable the search controller's animation that hides the large title once input has started. This can be done like so:
navigationItem.titleView = searchController.searchBar
searchController.hidesNavigationBarDuringPresentation = false