Question

我正在尝试学习核心数据并遵循youtube的一些教程。在自己练习代码时，我正在尝试创建＆＃34; NSManagedObjectContext＆＃34;通过传递＆＃34; managedObjectContext＆＃34;消息到app委托对象。以下是代码：

+ (Employee *)addEmployeeDetails:(NSDictionary *)employeeData {
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    Employee *employeeEntity = nil;

    return employeeEntity;
}

我收到了此问题标题中提到的错误。我记得我选择了＃34;使用核心数据＆＃34;创建项目时的选项。我错过了项目中的其他内容吗？

以下是与项目一起自动添加的AppDelegate文件的内容。

AppDelegate.h

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (readonly, strong) NSPersistentContainer *persistentContainer;
- (void)saveContext;
@end

AppDelegate.m

#import "AppDelegate.h"

@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    return YES;
}


- (void)applicationWillResignActive:(UIApplication *)application {
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
}


- (void)applicationDidEnterBackground:(UIApplication *)application {
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}


- (void)applicationWillEnterForeground:(UIApplication *)application {
    // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}


- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}


- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}


#pragma mark - Core Data stack

@synthesize persistentContainer = _persistentContainer;

- (NSPersistentContainer *)persistentContainer {
    // The persistent container for the application. This implementation creates and returns a container, having loaded the store for the application to it.
    @synchronized (self) {
        if (_persistentContainer == nil) {
            _persistentContainer = [[NSPersistentContainer alloc] initWithName:@"Core_Data_Tutorial_1"];
            [_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *storeDescription, NSError *error) {
                if (error != nil) {
                    // Replace this implementation with code to handle the error appropriately.
                    // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

                    /*
                     Typical reasons for an error here include:
                     * The parent directory does not exist, cannot be created, or disallows writing.
                     * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                     * The device is out of space.
                     * The store could not be migrated to the current model version.
                     Check the error message to determine what the actual problem was.
                    */
                    NSLog(@"Unresolved error %@, %@", error, error.userInfo);
                    abort();
                }
            }];
        }
    }

    return _persistentContainer;
}

#pragma mark - Core Data Saving support

- (void)saveContext {
    NSManagedObjectContext *context = self.persistentContainer.viewContext;
    NSError *error = nil;
    if ([context hasChanges] && ![context save:&error]) {
        // Replace this implementation with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog(@"Unresolved error %@, %@", error, error.userInfo);
        abort();
    }
}

@end

Answer 1

AppDelegate没有名为managedObjectContext的媒体资源。您需要在AppDelegate.h

中声明它

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;

当然，请正确分配。

没有可见的@interface为＆＃39; Appdelegate＆＃39;声明选择器＆＃39; managedObjectContext＆＃39;

1 个答案: