使用 prepare for segue 将托管对象上下文从 ViewController 传递到 TarBarViewController答案

【问题标题】：Pass Managed Object Context from a ViewController to TarBarViewController using prepare for segue使用 prepare for segue 将托管对象上下文从 ViewController 传递到 TarBarViewController
【发布时间】：2012-03-08 20:22:08
【问题描述】：

我正在尝试从 ViewController 传递核心数据托管对象上下文（它能够从 AppDelegate 加载相同的内容到 TabBarViewController。

AppDelegate.m

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

LoginViewController.m

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if([segue.identifier isEqualToString:@"LoginSegue"]){
        UITabBarController *tabBarViewController = (UITabBarController *) [segue destinationViewController];
        ReceiptsListViewController *receiptsListViewController = (ReceiptsListViewController *) [[tabBarViewController viewControllers] objectAtIndex:5];
        receiptsListViewController.managedObjectContext = self.managedObjectContext;
    }
}

当我运行它时，我遇到了这个错误

2012-03-09 01:47:03.723 Peets[22893:fb03]-[UINavigationController setManagedObjectContext:]：无法识别的选择器发送到实例 0x6d91900
2012-03-09 01:47:03.747 Peets[22893:fb03] *** WebKit 在 webView 中丢弃了一个未捕获的异常：shouldInsertText:replacingDOMRange:givenAction: delegate:  -[UINavigationController setManagedObjectContext:]: unrecognized selector sent to实例 0x6d91900

【问题讨论】：

标签： ios core-data nsmanagedobjectcontext segue

【解决方案1】：

我不完全了解您希望如何将 MOC 从 VC 传递到 TBVC。通常 RootViewController 是 TBVC。如果您也是这种情况，您可以像这样通过 MOC：

#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 Master-Detail Application 模板。默认情况下它没有 TBVC，但如果您像屏幕截图中那样添加 TBVC，上面的代码将起作用。

【讨论】：

【解决方案2】：

您正在尝试在 UINavigationController 上设置 NSManagedObjectContext。

ReceiptsListViewController *receiptsListViewController = (ReceiptsListViewController *) [[tabBarViewController viewControllers] objectAtIndex:5] 是你的问题，因为它返回 UINavigationController。

【讨论】：