swift - 从Navigation改为TabBar，CoreData不加载

Question

我将导航 Controller 更改为选项卡栏 Controller ，然后我想编译该应用程序。但它不再加载我的 ManagedContext。

这是我加载应用程序时的启动代码:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    guard let navController = window?.rootViewController as? UINavigationController,
        let viewController = navController.topViewController as? ViewController else {
            return true
    }
    viewController.managedContext = coreDataStack.managedContext
    // Override point for customization after application launch.
    return true
}

因此我尝试像这样编辑代码:

编辑:

       func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let controller = storyboard.instantiateInitialViewController()
        //let controller = storyboard.instantiateViewController(withIdentifier: "TabBarVC")
        self.window?.rootViewController = controller



        guard let tabController = window?.rootViewController as? UITabBarController,
            let navController = tabController.viewControllers![0] as? UINavigationController,
            let viewController = navController.topViewController as? ViewController else {
                return true

        }
//  Version that works for UINavigationCOntroller 
//        guard let navController = window?.rootViewController as? UINavigationController,
//            let viewController = navController.topViewController as? ViewController else {
//                return true
//        }
        viewController.managedContext = coreDataStack.managedContext
        // Override point for customization after application launch.
        return true
    }

我改了代码，但还是无法加载managementContext，当我想在ViewController中使用它时，它返回nil，我还将初始Viewcontroller设置为tabBarController。

Answer 1

首先为您的窗口设置rootviewcontroller，然后再纠正您的逻辑。

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let storyboard = UIStoryboard(<StoryboardName>, bundle: nil)
    let controller = storyboard.initializeInitialViewController()
    window.rootViewController = controller
        guard let navController = window?.rootViewController as? UITabBarController,
            let viewController = navController.moreNavigationController as? ViewController else {
                return true
        }
        viewController.managedContext = coreDataStack.managedContext
        // Override point for customization after application launch.
        return