頂視圖控制器錯誤

Question

我有一個根視圖控制器的困難。

enter image description here圖片（1）

在下面的代碼和圖片1，一切工作正常。 但圖片2 enter image description here圖片（2）中，我得到了一個錯誤說

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[BannerViewController topViewController]: unrecognized selector sent to instance 0x7feb9b64dbc0'

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { 

    UITabBarController *tabBarController = (UITabBarController *)self.window.rootViewController; 
    UINavigationController *navController = tabBarController.viewControllers[0]; 

    ItemListTableViewController *itemList = (ItemListTableViewController *)navController.topViewController; 
    itemList.managedObjectContext = self.managedObjectContext; 

    return YES; 
} 

所以，請幫助我如何在導航控制器的前面插入一個視圖控制器？

Answer 1

您可以通過容器VC的childViewControllers財產得到導航控制器參考：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { 
    UITabBarController *tabBarController = (UITabBarController *)self.window.rootViewController; 
    UIViewController *containerVC = tabBarController.viewControllers[0]; 
    UIView *containerVCview = containerVC.view; 
    UINavigationController *navController = containerVC.childViewControllers[0]; 

    ItemListTableViewController *itemList = (ItemListTableViewController *)navController.topViewController; 
    itemList.managedObjectContext = self.managedObjectContext; 

    return YES; 
}