ios - UISearchBar が起動しない

Question

UISearchController の検索バーをナビゲーション バーの titleView に配置しました。しかし、タップして検索すると、UISearchBar が応答しません。原因は何ですか？

        let tvController:UITableViewController = UITableViewController()
        tvController.tableView.delegate = self
        tvController.tableView.dataSource = self
        self.searchController = UISearchController(searchResultsController: tvController)
        self.searchController?.searchResultsUpdater = self
        self.searchController!.searchBar.placeholder = "Search for places"
        self.searchController!.hidesNavigationBarDuringPresentation = false
        self.searchController!.dimsBackgroundDuringPresentation = false;
        self.searchController!.searchBar.searchBarStyle = UISearchBarStyle.Prominent
        self.searchController!.delegate = self
        self.searchController!.searchBar.delegate = self
        self.definesPresentationContext = true
        self.searchController!.searchBar.sizeToFit()
        self.navigationItem.titleView = self.searchController!.searchBar