使用选项卡栏控制器呈现视图控制器

Question

好的，所以每次我尝试使用以下代码呈现一个视图控制器(来自AppDelegate文件的"didFinishLaunchingWithOptions"函数(时，我的带有4个项目的tabBar消失了，即使显示了我想要的ViewController：

    let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: Bundle.main)
    let tabBarController = storyBoard.instantiateViewController(withIdentifier: "theEvents") as! ThirdViewController
    self.window?.rootViewController? = tabBarController

当我尝试以下代码(也在AppDelegate文件的"didFinishLaunchingWithOptions"函数中(时，我什么也得不到：

    let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: Bundle.main)
    let tabBarController = storyBoard.instantiateViewController(withIdentifier: "theEvents") as! ThirdViewController
    self.window?.rootViewController?.tabBarController?.didMove(toParentViewController: tabBarController)

我已经尝试了两者的几次迭代，但我似乎仍然无法得到我想要的......

从本质上讲，我想要以编程方式按下其中一个按钮，以便我的第三个视图控制器成为用户在某些情况下看到的第一个视图。

任何帮助将不胜感激！

Answer 1

目前还不清楚ThirdViewController到底是什么，但我猜它是选项卡控制器第三个选项卡中包含的视图控制器。

标签栏控制器仍然需要是窗口的rootViewController。

如果您只想以编程方式选择选项卡栏控制器的某个索引，则可以执行以下操作：

        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let tabVC = storyboard.instantiateViewController(withIdentifier: "tabVC") as! UITabBarController  // however you defined your UITabBarController.
        tabVC.selectedIndex = 2   // or whatever you want
        window?.rootViewController = tabVC

如果标签栏控制器已经是根，那么您可以绕过实例化它并将其设置为根的步骤：

    if let tabVC = window?.rootViewController as? UITabBarController {
        tabVC.selectedIndex = 2
    }

Answer 2

好的，这就是我为我的应用程序所做的，我所做的是，我总是导航到 MainView 并调用 performSegue 进行导航。然后我按视图控制器

class AppDelegate: UIResponder, UIApplicationDelegate {
var shortcutItem: UIApplicationShortcutItem?
var mainViewController:MainViewController?
static var  handled = false
enum ShortcutIdentifier: String {
    case AddExpense
    case AddIncome
    case AddExpenseType
    case AddIncomeType
    init?(fullIdentifier: String) {
        guard let shortIdentifier = fullIdentifier.components(separatedBy: ".").last else {
            return nil
        }
        self.init(rawValue: shortIdentifier)
    }

    func getUIViewController(storyboard : UIStoryboard) -> UIViewController{
        return storyboard.instantiateViewController(withIdentifier:self.rawValue)
    }
}

func application(_ application: UIApplication, performActionFor shortcutItem: UIApplicationShortcutItem, completionHandler: @escaping (Bool) -> Void) {
    self.shortcutItem = shortcutItem
    completionHandler(handleShortcut(shortcutItem))
}

@discardableResult fileprivate func handleShortcut(_ shortcutItem: UIApplicationShortcutItem) -> Bool {
    let shortcutType = shortcutItem.type
    guard let shortcutIdentifier = ShortcutIdentifier(fullIdentifier: shortcutType) else {
        return false
    }
    return selectTabBarItemForIdentifier(shortcutIdentifier)
}
fileprivate func selectTabBarItemForIdentifier(_ identifier: ShortcutIdentifier) -> Bool {
    if AppDelegate.handled  {
        return false
    }
    var handled = false
    guard let tabBarController = self.window?.rootViewController as? UITabBarController else {
        return false
    }
    tabBarController.selectedIndex = 1
    if let contentViewController  = tabBarController.selectedViewController?.contentViewController as? MainViewController  {
        mainViewController = contentViewController
    }else{
        guard let  navigationController = tabBarController.selectedViewController?.contentViewController.navigationController else {
            return false
        }

        print(type(of:navigationController.contentViewController))
        print(navigationController.viewControllers.count)
        let _ = navigationController.popToRootViewController(animated: true)
    }
    guard let rootView = mainViewController else {
        return false
    }
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    switch (identifier) {
    case .AddExpense:
        rootView.performSegue(withIdentifier: "Expences", sender: rootView)
        handled = true
    case .AddIncome:
        rootView.performSegue(withIdentifier: "Incomes", sender: rootView)
        handled = true
    case .AddExpenseType:
        rootView.performSegue(withIdentifier: "Expences Types", sender: rootView)
        handled = true
    case .AddIncomeType:
        rootView.performSegue(withIdentifier: "Incomes Types", sender: rootView)
        handled = true
    }
    rootView.navigationController!.pushViewController(identifier.getUIViewController(storyboard: storyboard), animated: true)
    AppDelegate.handled = handled
    return handled
}
var window: UIWindow?

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let theme = ThemManager.currentTheme()
    ThemManager.applyTheme(theme: theme)
    var performShortcutDelegate = true
    if let shortcutItem = launchOptions?[UIApplicationLaunchOptionsKey.shortcutItem] as? UIApplicationShortcutItem {
        print("Application launched via shortcut")
        self.shortcutItem = shortcutItem
        performShortcutDelegate = false
    }
    return performShortcutDelegate
}

func applicationDidEnterBackground(_ application: UIApplication) {
    AppDelegate.handled = false
}
func applicationDidBecomeActive(_ application: UIApplication) {
    print("Application did become active")
    guard let shortcut = shortcutItem else { return }
    print("- Shortcut property has been set")
    handleShortcut(shortcut)
    AppDelegate.handled = true
    self.shortcutItem = nil
}

}