中心UILabel的工具栏中间上的键盘

我怎么能中心的一个标签，在中间的键盘的工具栏？ 我可以得到的标签中间的键盘，但它没有为中心的正确

lazy var textView: UITextView = {
    // ...
}()

lazy var dummyToolBarButton: UIButton = {
    let button = UIButton(type: .system)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.setImage(UIImage(named: "cogIcon"), for: .normal)
    button.alpha = 0
    button.sizeToFit()
    return button
}()

lazy var timerLabel: UILabel = {
    let label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false
    label.text = "00:00"
    label.font = UIFont.monospacedDigitSystemFont(ofSize: 15.5, weight: .regular)
    label.backgroundColor = .clear
    label.textColor = .gray
    label.textAlignment = .center
    label.sizeToFit()
    return label
}()

override func viewDidLoad() {
    super.viewDidLoad()

    setToolBarOnKeyboard()
}

func setToolBarOnKeyboard() {
    
    let toolBar = UIToolbar()
    toolBar.sizeToFit()
    
    let invisibleDummyButton = UIBarButtonItem(customView: dummyToolBarButton) // alpha is set to 0
    
    let flexibleSpaceLeft = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
    
    let labelItem = UIBarButtonItem(customView: timerLabel)
    
    let flexibleSpaceRight = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
    
    let doneButton = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(dismissKeyboard))
    
    toolBar.setItems([invisibleDummyButton, flexibleSpaceLeft, labelItem, flexibleSpaceRight, doneButton], animated: false)
    
    textView.inputAccessoryView = toolBar
}

@objc func dismissKeyboard() { }