ios - 使用segue for segue将托管对象上下文从ViewController传递到TarBarViewController

我正在尝试从ViewController传递核心数据托管对象上下文（它能够将其从AppDelegate加载到TabBarViewController。

AppDelegate.m
ojit_pre

LoginViewController.m

ojit_preWhen i run it i encounter this error

// Pass the managed object context to the root view controller (the login view)
LoginViewController *rootViewController = (LoginViewController *)self.window.rootViewController;
rootViewController.managedObjectContext = self.managedObjectContext;

最佳答案

我不完全了解如何将MOC从VC传递到TBVC。通常，RootViewController是TBVC。如果您也是这种情况，则可以通过MOC，如下所示：

#import "AppDelegate.h"
#import "MasterViewController.h"

@implementation AppDelegate

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    UITabBarController *tabController = (UITabBarController *)self.window.rootViewController;

    UINavigationController *navigationController = (UINavigationController *)[[tabController viewControllers] objectAtIndex:0];
    MasterViewController *controller = (MasterViewController *)[[navigationController viewControllers] objectAtIndex:0];
    controller.managedObjectContext = self.managedObjectContext;

    navigationController = (UINavigationController *)[[tabController viewControllers] objectAtIndex:1];
    controller = (MasterViewController *)[[navigationController viewControllers] objectAtIndex:0];
    controller.managedObjectContext = self.managedObjectContext;

    navigationController = (UINavigationController *)[[tabController viewControllers] objectAtIndex:2];
    controller = (MasterViewController *)[[navigationController viewControllers] objectAtIndex:0];
    controller.managedObjectContext = self.managedObjectContext;

    return YES;
}

顺便说一句：此示例基于Xcode中的主从应用程序模板。默认情况下，它没有TBVC，但是如果您添加TBVC（如屏幕截图所示），则上面的代码将起作用。