SearchBar切断导航栏内部

Question

我正在导航栏中处理非常简单的动画：我有导航栏，右侧有2个按钮。在搜索图标点击我动画导航栏，以便它隐藏按钮和搜索图标，并显示搜索栏。在取消按钮点击它相反。简单

 lazy var searchBar:UISearchBar = UISearchBar()

override func viewDidLoad() {
    super.viewDidLoad()
    self.automaticallyAdjustsScrollViewInsets = false
    searchBar.delegate = self
    searchBar.backgroundColor = UIColor.darkGray
    searchBar.tintColor = UIColor(red: 140/255, green: 195/255, blue: 65/255, alpha: 1.0)

}

点击搜索按钮时，搜索栏会添加到导航栏中，但左侧和右侧略微剪掉。

 @IBAction func subjectTapped(_ sender: Any) {

    self.navigationItem.setRightBarButtonItems(nil, animated: true)
    self.navigationItem.setLeftBarButtonItems(nil,animated: true)
    self.navigationItem.titleView = nil
    searchBar.placeholder = "I am looking for ..."
    searchBar.alpha = 0
    self.navigationItem.titleView = searchBar

    UIView.animate(withDuration: 0.5, animations: {
        self.searchBar.alpha = 1
    }, completion: { finished in
        self.searchBar.becomeFirstResponder()
    })

}

请告诉我我做错了什么，并解决了这个问题