         let complete = TabNavigationItem(title: "完成", target: self, selector: #selector(_handleCompleteAction(_:)))
         setTabNavigationItems([complete, cancel])
         
-        _setupBackToTopButton()
         // Load data of table view.
         tableView.reloadData()
     }

        
        return (lightColor, darkColor)
    }
    
    fileprivate func _setupBackToTopButton() {
        guard let tabNavigationBar = tabNavigationController?.tabNavigationBar else {
            return
        }
        _backToTopButton = UIButton(type: .system)
        _backToTopButton.translatesAutoresizingMaskIntoConstraints = false
        _backToTopButton.setImage(#imageLiteral(resourceName: "back_to_top"), for: .normal)
        _backToTopButton.tintColor = UIColor.application.titleColor
        _backToTopButton.addTarget(self, action: #selector(_handleBackToTop(_:)), for: .touchUpInside)
        tabNavigationBar.addSubview(_backToTopButton)
        _backToTopButton.centerXAnchor.constraint(equalTo: tabNavigationBar.centerXAnchor).isActive = true
        _backToTopButton.widthAnchor.constraint(equalToConstant: 44.0).isActive = true
        _backToTopButton.heightAnchor.constraint(equalToConstant: 44.0).isActive = true
        _backToTopButton.lastBaselineAnchor.constraint(equalTo: tabNavigationBar.lastBaselineAnchor).isActive = true
    }
}

// MARK: - Storyboard Supporting.

            realm.add(category)
        }
        self.tabNavigationController?.dismiss(animated: true, completion: nil)
    }
}

