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我创建了一个 Core Data 应用程序，并从中获取了 .xcdatamodel 文件并将其添加到另一个 iOS 应用程序中。这个新应用程序是一个 SingleView 应用程序，我现在正在尝试连接到这个 .xcdatamodel 文件来运行 Core Data 函数。我所做的是创建了一个 Singleton 类，通过它我调用一个实例方法：

NSManagedObjectContext *context = [[SingletonDB sharedInstance] managedObjectContext];

managedObjectContext 方法如下所示：

- (NSManagedObjectContext *) managedObjectContext{

    static NSManagedObjectContext *context = nil;

    if(context){
        return context;
    }

    NSPersistentStoreCoordinator *coordinator = nil;

    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"MyTestDatabase" withExtension:@"momd"];
    NSManagedObjectModel *objectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

    NSLog(@"%@", [objectModel entities]);
 ...
}

在“managedObjectContext”方法中，由于某种原因，modelURL 的值为 nil，从而导致 RuntimeException：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot create an NSPersistentStoreCoordinator with a nil model'

我是否错过了导致此错误的步骤？当我选择 MyTestDB.xcdatamodel 文件时，我看到了我在之前的应用程序中创建的完整核心数据模式，现在由于某种原因我无法读取数据。我还尝试将扩展名从“momd”更改为“mom”，但这只会将 RuntimeException 更改为：

'NSInvalidArgumentException', reason: 'Cannot create an SQL store with a nil URL.'

问题可能是什么？

4

1 回答 1

0

尝试这个，

   + (NSManagedObjectModel *)managedObjectModel
    {
        static NSManagedObjectModel *managedObjectModel;
        if (managedObjectModel != nil) {
            return managedObjectModel;
        }
        NSString * modelPath = [[NSBundle mainBundle] pathForResource:@"MyTestDatabase" ofType:@"momd"];
        managedObjectModel = [[NSManagedObjectModel alloc]initWithContentsOfURL:[NSURL fileURLWithPath:modelPath]];

        return managedObjectModel;
    }

    +(NSPersistentStoreCoordinator *)persistentStoreCoordinator{
        static NSPersistentStoreCoordinator * persistentStoreCoordinator;
        if (persistentStoreCoordinator != nil) {
            return persistentStoreCoordinator;
        }

        NSError *error=nil;
        NSString *storePath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"MyTestDatabase.sqlite"];

        NSURL *storeUrl =[NSURL fileURLWithPath:storePath];
        persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

        if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error])
        {
            NSLog(@"store url %@",storeUrl);
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            exit(-1);
        }    



        return persistentStoreCoordinator;
    }

    +(NSManagedObjectContext *)managedObjectContext
    {
        static NSManagedObjectContext * managedObjectContext;
        if(managedObjectContext!=nil){
            return managedObjectContext;
        }
        @try {
            NSPersistentStoreCoordinator * coordinator = [self persistentStoreCoordinator];
            if (coordinator != nil) {
                managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
                [managedObjectContext setPersistentStoreCoordinator: coordinator];
            }
        }
        @catch (NSException *exception) {
            NSLog(@"Exception occur %@",exception);
        }
        return managedObjectContext;

    }
于 2013-09-26T04:48:27.707 回答