但当它成为第一响应者时,UISearchBar的宽度变为0,它看起来像这样：

现在唯一的约束是右边的UIButton的宽度是44pt,整个堆栈视图固定在屏幕的顶部和侧面.这是控制台打印出来的：

我不太熟悉NSLayoutConsTraint,但显然有些东西与按钮上的44pt宽度约束相冲突.为什么UISearchbar的宽度变为0？

这是我的代码：

override func didTransition(to presentationStyle: MSmessagesAppPresentationStylE) {
    if presentationStyle == .expanded {
        searchController.searchBar.becomeFirstResponder()
        searchController.searchBar.TintColor = UIColor.white
    }
}

func didDismissSearchController(_ searchController: UISearchController) {
    requestPresentationStyle(.compact)
}

override func viewDidLoad() {
    super.viewDidLoad()
    configureSearchController()
}

func configureSearchController() {
    searchController = UISearchController(searchResultsController: nil)
    searchController.dimsBACkgroundDuringPresentation = false
    searchController.searchBar.placeholder = "Search here..."
    searchController.searchBar.sizeToFit()
    searchController.searchBar.isTranslucent = false
    searchController.searchBar.delegate = self
    searchController.delegate = self
    searchController.searchBar.barTintColor = addButton.BACkgroundColor
    stackView.insertArrangedSubview(searchController.searchBar,at: 0)
    //This removes the hairline
    let color = addButton.BACkgroundColor
    searchController.searchBar.layer.borderWidth = 1
    searchController.searchBar.layer.borderColor = color?.cgColor

}

func searchBarShouldBeginEdiTing(_ searchBar: UISearchBar) -> Bool {
    if presentationStyle == .expanded {
        return true
    } else {
        requestPresentationStyle(.expanded)
        return false
    }
}

我的故事板按要求：

解决方法