UIViewcontroller 在切换标签后消失 UITabBarController

Question

我正在开发一个使用 UITabBarController 的应用程序，并且突然停止出现一个 tabItem。然后我开始调查并最终发现与UISearchController 和UITabBarController 相关的问题。

为了隔离问题，构建一个简单的应用程序来演示情况。

这就是我在didFinishLaunchingWithOptions 上实例化 TabBar 的方式：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    self.window = UIWindow(frame: UIScreen.main.bounds)
    self.window?.backgroundColor = .white

    let first:SearchController = {
        let sc = SearchController()
        sc.tabBarItem = UITabBarItem(title: "First", image: UIImage(named:"iphone"), tag: 0)
        return sc
    }()

    let second:SecondViewController = {
        let s = SecondViewController()
        s.tabBarItem = UITabBarItem(title: "Second", image: UIImage(named:"iphone"), tag: 1)
        return s
    }()

    let tabBar = UITabBarController()
    let controllers = [first, second]
    tabBar.viewControllers = controllers.map {
        UINavigationController(rootViewController: $0)
    }


    self.window?.rootViewController = tabBar
    self.window?.makeKeyAndVisible()
    return true
}

这是带有 UISearchController 的 viewController：

class SearchController: UIViewController {
    var matchingItems:[String] = [] {
        didSet{
            self.tableView.reloadData()
        }
    }

    lazy var searchController:UISearchController = UISearchController(searchResultsController: nil)

    lazy var tableView: UITableView = { [unowned self] in
        let tv = UITableView(frame: CGRect.zero, style: .grouped)
        tv.translatesAutoresizingMaskIntoConstraints = false
        tv.delegate = self
        tv.dataSource = self
        tv.register(UITableViewCell.self, forCellReuseIdentifier: "id")
        return tv
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        title = "First"
        view.addSubview(self.tableView)
        self.navigationItem.searchController = searchController
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        self.perform(#selector(showKeyboard), with: nil, afterDelay: 0.1)
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        searchController.searchBar.resignFirstResponder()
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        let layout = self.view.safeAreaLayoutGuide
        tableView.topAnchor.constraint(equalTo: layout.topAnchor).isActive = true
        tableView.bottomAnchor.constraint(equalTo: layout.bottomAnchor).isActive = true
        tableView.rightAnchor.constraint(equalTo: layout.rightAnchor).isActive = true
        tableView.leftAnchor.constraint(equalTo: layout.leftAnchor).isActive = true
    }

    @objc func showKeyboard() {
        self.searchController.searchBar.becomeFirstResponder()
        self.searchController.searchBar.text = ""
    }
}

在运行时，当系统完成渲染此视图控制器时，调试控制台会打印：

SearchBar+TabBar[15454:895018] [MC] Reading from private effective user settings.
2018-04-22 12:07:19.595887-0300 SearchBar+TabBar[15454:895018] +[CATransaction synchronize] called within transaction
2018-04-22 12:07:19.608090-0300 SearchBar+TabBar[15454:895018] +[CATransaction synchronize] called within transaction
2018-04-22 12:07:19.608269-0300 SearchBar+TabBar[15454:895018] +[CATransaction synchronize] called within transaction
2018-04-22 12:07:19.608516-0300 SearchBar+TabBar[15454:895018] +[CATransaction synchronize] called within transaction

在stackoverflow上搜索我发现这条消息+[CATransaction synchronize] called within transaction 与在主线程中渲染多个动画有关。

我想知道这个视图控制器可视化问题是否与此有关。所以我在 SearchController 类中注释了searchController 实例化行：

self.navigationItem.searchController = searchController

现在UITabBarController 在我的第一个视图控制器中没有UISearchController 也能完美运行。

我的问题是：

1. 是否有另一种方法来实例化 UISearchController 以避免 这个？
2. 如果是，我应该怎么做？

带有示例代码的 GitHub 存储库：sample code

Answer 1

我的一个朋友建议在didFinishLaunchingWithOptions 中添加UITabBarController 作为UINavigationController 的根，它可以完美地工作并解决问题：

let tabBar = UITabBarController()
let controllers = [first, second]
tabBar.viewControllers = controllers.map {
    UINavigationController(rootViewController: $0)
}


let nav = UINavigationController(rootViewController: tabBar)
nav.isNavigationBarHidden = true
nav.navigationBar.isUserInteractionEnabled = false

Answer 2

在你的 TabBarController 类中实现这个功能：

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool

在这个函数中，你应该检查之前是否选择了带有 searchBar 的 Controller 并使 SearchController 处于非活动状态

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    if (tabBarController.selectedIndex == ControllerWithSearchBarIndex) {
        ((viewControllers![ControllerWithSearchBarIndex] as! UINavigationController).viewControllers.first! as! ControllerWithSearchBarIndex).searchController.isActive = false
    }
    return true
}

Answer 3

使用 tableView 在视图控制器上设置definesPresentationContext = true（在您的示例中为SearchController）。这将允许UISearchController 在您切换标签时保持活动状态。