刷新控制UI失败（SWIFT）

Question

我对刷新控制有一点问题。一切看起来不错但是当我导航到另一个视图控制器然后回来时，我得到了以下灰色空间：

我的代码：

override func viewDidLoad() {
    super.viewDidLoad()

    self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: UIImage(named: "add_employee.png"), style: UIBarButtonItemStyle.Plain, target: self, action: "showEmployeeRegisterView")
    self.navigationItem.rightBarButtonItem = UIBarButtonItem(image: UIImage(named: "sync.png"), style: UIBarButtonItemStyle.Plain, target: self, action: "syncData")

    self.refreshControl = UIRefreshControl()
    self.refreshControl.backgroundColor = UIColor.grayColor()
    self.refreshControl.tintColor = UIColor.whiteColor()

    self.refreshControl.attributedTitle = NSAttributedString(string: "ACTUALIZAR", attributes: [NSForegroundColorAttributeName: UIColor.whiteColor()])
    self.refreshControl.addTarget(self, action: "loadData", forControlEvents: UIControlEvents.ValueChanged)

    self.searchController = UISearchController(searchResultsController: nil)
    self.searchController.searchBar.sizeToFit()
    self.searchController.searchBar.delegate = self
    self.searchController.searchResultsUpdater = self
    self.searchController.dimsBackgroundDuringPresentation = false
    self.searchController.searchBar.placeholder = "Buscar..."
    self.searchController.searchBar.translucent = false

    let nib = UINib(nibName: "CustomTableCell", bundle: nil)

    self.tblEmployee.registerNib(nib, forCellReuseIdentifier: "cell")
    self.tblEmployee.dataSource = self
    self.tblEmployee.addSubview(refreshControl)
    self.tblEmployee.tableHeaderView = searchController.searchBar

    self.definesPresentationContext = true
}

正确的用户界面：

那么，我做错了什么？