我正在尝试将 CoreData 添加到在 Xcode 4.2 中创建的现有 iOS 应用程序。由于它是基于标签栏的应用程序，因此我没有在创建时默认包含它的选项。

到目前为止我已经:

• 将 CoreData.framework 添加到应用程序(在构建目标中确认)
• 添加了一个模型'model.coredatamodeld'(在构建目标中确认，在iOS模拟器中运行时确认'mom'文件包含在应用程序目录中)
• 用新启用 CoreData 的应用程序自动生成的版本替换了应用程序委托(delegate)

我最终创建的对象模型返回 nil。如果我查看生成的 URL，它会指向我的文件系统中的“mom”文件夹。该文件夹包含“model.momd”和“VersionInfo.plist”。这两个文件的内容看起来都很合理(前者是一些二进制数据，后者是一些听起来合理的 XML)。

__managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL: modelURL];
// __managedObjectModel is nil here

如何调试？

下面是 App delegate 的来源。

#import "AppDelegate.h"
#import <CoreData/CoreData.h>

@implementation AppDelegate

@synthesize window = _window;
@synthesize managedObjectContext = __managedObjectContext;
@synthesize managedObjectModel = __managedObjectModel;
@synthesize persistentStoreCoordinator = __persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    id ctx   = self.managedObjectContext;
    //id model = [self managedObjectModel];
    //NSLog(@"%@ %@", ctx, model);
    return YES;
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}

- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil)
    {
        if ([managedObjectContext hasChanges] && ![managedObjectContext 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();
        } 
    }
}

#pragma mark - Core Data stack

/**
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
 */
- (NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}

/**
 Returns the managed object model for the application.
 If the model doesn't already exist, it is created from the application's model.
 */
- (NSManagedObjectModel *)managedObjectModel
{
    if (__managedObjectModel != nil)
    {
        return __managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"model" withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL: modelURL];

    NSError *error = nil;
    NSData *objectIDData = [NSData dataWithContentsOfURL:modelURL options:NSDataReadingMapped error:&error];
    NSLog(@"%@",objectIDData);

    return __managedObjectModel;
}

/**
 Returns the persistent store coordinator for the application.
 If the coordinator doesn't already exist, it is created and the application's store added to it.
 */
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"model.sqlite"];

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&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. 

         Typical reasons for an error here include:
         * The persistent store is not accessible;
         * The schema for the persistent store is incompatible with current managed object model.
         Check the error message to determine what the actual problem was.


         If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.

         If you encounter schema incompatibility errors during development, you can reduce their frequency by:
         * Simply deleting the existing store:
         [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]

         * Performing automatic lightweight migration by passing the following dictionary as the options parameter: 
         [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

         Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.

         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}

#pragma mark - Application's Documents directory

/**
 Returns the URL to the application's Documents directory.
 */
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

@end

最佳答案

我在这上面浪费了足够的时间，只是创建了一个具有所需“基本功能”(核心数据、 Storyboard、ARC 等)的新项目，然后将我的代码放入其中。这并不是最好的解决方案，但只用了大约 10 分钟，而且更重要的是，它奏效了。

关于ios - 将 CoreData 添加到现有的 iOS 项目 - 无法获取 NSManagedObjectModel，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8295267/