uisearchbar doesn't get focus

Hey there,

I have a problem with a search bar inside the navigation controller, because it doesn't get focus by code like it should. I want to achieve similar behavior, like the search bar in the calendar app has. I have a search icon in the navigation bar. If pressed, I segue to a new view controller and add a search bar to the navigation bar through code. Then I animate the nav bar in and the search text field should get focus automatically, so that the keyboard opens and everything. But this does not happen. If I click the field manually, the keyboard appears, but there is no blinking cursor inside the text field. Here is the code I use to create the search controller and bar. Last two lines seem not to do anything. I have already double checked, that searchController is not nil.

class WOSSearchViewController: UIViewController, UISearchBarDelegate, UISearchResultsUpdating, UISearchControllerDelegate, UITableViewDataSource, UITableViewDelegate {


    var searchController: UISearchController? = nil
    var searchResults: [WOSSearchResult] = []
   
    override func viewDidLoad() {
      
        super.viewDidLoad()
        
        searchController = UISearchController(searchResultsController: nil) 
        searchController?.searchResultsUpdater = self
        searchController?.delegate = self
        searchController?.searchBar.delegate = self
        searchController?.dimsBackgroundDuringPresentation = false
        searchController?.hidesNavigationBarDuringPresentation = false
        searchController?.searchBar.showsCancelButton = true
        searchController?.searchBar.sizeToFit()
        navigationItem.titleView = searchController?.searchBar
      
        navigationController?.setNavigationBarHidden(true, animated: false)
    }
  
    override func viewDidAppear(animated: Bool) {
      
        super.viewDidAppear(animated)
      
        navigationController?.setNavigationBarHidden(false, animated: true)

        UIView.animateWithDuration(0.2, animations: {() -> Void in
            self.view.layer.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).CGColor
        })
      
        searchController?.searchBar.becomeFirstResponder()                    // does not work
        searchController?.searchBar.window?.makeKeyAndVisible()               // does not work
       
    }
}

Thanks for any help.