     
     lazy private var _tabNavigationBar: TabNavigationBar = _createGeneralTabNavigationBar()
     
-    #if swift(>=4.0)
-    #else
-    public override var keyboardAlignmentLayoutGuide: UILayoutSupport { return _keyboardAlignmentView }
-    #endif
-    lazy fileprivate var _keyboardAlignmentView: _TabNavigationKeyboardAlignmentLayoutView = _createGeneralAlignmentView()
-    fileprivate var _keyboardAlignmentViewHeightConstraint: NSLayoutConstraint!
+    // #if swift(>=4.0)
+    // #else
+    // public override var keyboardAlignmentLayoutGuide: UILayoutSupport { return _keyboardAlignmentView }
+    // #endif
+    // lazy fileprivate var _keyboardAlignmentView: _TabNavigationKeyboardAlignmentLayoutView = _createGeneralAlignmentView()
+    // fileprivate var _keyboardAlignmentViewHeightConstraint: NSLayoutConstraint!
     
     public var interactivePopGestureRecognizer: UIPanGestureRecognizer { return _panGestureRecognizer }
     fileprivate var _panGestureRecognizer: UIPanGestureRecognizer!

        _setSelectedViewController(at: index, updateNavigationBar: true, updateNavigationItems: !isTabNavigationItemsUpdatingDisabledInRootViewControllers, animated: animated)
    }
    
    public func addViewController<T>(_ viewController: T) where T: UIViewController, T: TabNavigationReadable {
        if isViewLoaded {
            // Add view controller as child view controller if view of tab-navigation controller loaded.
            _addViewControllerWithoutUpdatingNavigationTitle(viewController)

    return bar
}

private func _createGeneralAlignmentView() -> TabNavigationController._TabNavigationKeyboardAlignmentLayoutView {
    let view = TabNavigationController._TabNavigationKeyboardAlignmentLayoutView()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.backgroundColor = .clear
    view.clipsToBounds = true
