         // NotificationCenter.default.addObserver(self, selector: #selector(_handleKeyboardWillChangeFrameNotification(_:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
         NotificationCenter.default.addObserver(self, selector: #selector(_handleKeyboardWillChangeFrameNotification(_:)), name: NSNotification.Name.UIKeyboardWillChangeFrame, object: nil)
         // NotificationCenter.default.addObserver(self, selector: #selector(_handleKeyboardWillChangeFrameNotification(_:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
+        // Add tap to scroll to top gesture.
+        _tabNavigationBar.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(_handleTapTopOfTabNavigationBar(_:))))
     }
     
     deinit {

    }
    
    // MARK: - Actions.
    
    @objc
    private func _handlePanGestureRecognizer(_ sender: UIPanGestureRecognizer) {

    }
}

// MARK: ScrollView's scrolling to top.

extension UIViewController {
    open func makeViewScrollToTopIfNecessary(at location: CGPoint) {}
}

extension ViewController {
    override func removeFromParentViewController() {
        super.removeFromParentViewController()
