Question

首先，我会提到我在这个网站和其他网站上看到过很多关于此类问题的答案，但我似乎无法将这些解决方案与我的问题联系起来。不过，如果我正在寻找的答案已经存在，或者事实证明非常简单（尽管我绝对希望是这样），我会道歉。

我正在尝试将核心数据功能添加到现有应用程序中，并且我已采取以下步骤：

一个。将Core Data框架和CoreData导入添加到相关文件中湾将数据模型文件添加到名为“MyProject.xcdatamodeld”的Resources文件夹中，并将实体/属性添加到数据模型中。我还为每个实体制作了一个班级 C。在AppDelegate.h中添加了以下属性/方法：

@property (readonly, strong, nonatomic) NSManagedObjectModel* managedObjectModel;
@property (readonly, strong, nonatomic) NSManagedObjectContext* managedObjectContext;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator* persistentStoreCoordinator;

-(NSString*)applicationDocumentsDirectory;

d。将以下代码添加到我的AppDelegate.m：


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

-(NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];

    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }

    return __managedObjectContext;
}

-(NSManagedObjectModel *)managedObjectModel
{
    if (__managedObjectModel != nil)
    {
        return __managedObjectModel;
    }

    __managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];

    return __managedObjectModel;
}

-(NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }

    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"MyProject.sqlite"]];
    NSError *error = nil;

    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];

    if(![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error])
    {
        /*Error for store creation should be handled in here*/
    }

    return __persistentStoreCoordinator;
}

-(NSString *)applicationDocumentsDirectory
{
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

问题是，当这一行执行时：

__managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];

我收到一个NSInvalidArgumentException，表示正在将一个nil对象插入到NSArray中。

我尝试用以下内容替换该代码：

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

并且我没有得到任何例外，但在执行这些行之后__managedObjectModel仍为空。

我似乎无法弄清楚出了什么问题。有什么想法吗？

（作为旁注，我正在使用ARC，这就是为什么你没有看到任何保留的电话）。

非常感谢任何帮助/建议。

谢谢，

B.J。

Answer 1

如果在添加模型文件后重命名了模型文件，则可能会出现此问题。当我重命名我的模型时，我曾遇到过一个问题。要修复，我不得不将模型从项目目录中复制出来，从项目中删除它，然后重新添加它。

Answer 2

您实际上是在合并多个模型文件 - 还是仅添加新的Core Data后备存储？

您的代码看起来像要合并的模板......

我的核心数据堆栈如下所示：

    #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];
        [__managedObjectContext setUndoManager:nil];
    }
    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:@"FlurryStats" withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];    
    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:@"FlurryStats.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. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.

         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;
}

无法将Core Data功能添加到现有的iOS应用程序中

2 个答案: