NSFetchedResultsController的一个实例需要一个非零的fetchRequest和managedObjectContext？

Question

尝试使用Core Data时出现此错误：

  

***由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'NSFetchedResultsController的实例需要非零fetchRequest和managedObjectContext'

我在包含表视图的模态视图控制器中将错误追溯到此：

    - (void)setupFetchedResultsController
{
    NSString *entityName = @"Location";
    NSLog(@"Setting up a Fetched Results Controller for the Entity named %@", entityName);

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];

// ERROR OCCURS IN THE LINE BELOW vvv
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:nil
                                                                                   cacheName:nil];

    [self performFetch];
}

这就是我在AppDelegate中所拥有的：

    - (void)setupFetchedResultsController
{
    NSString *entityName = @"Location"; 
    NSLog(@"Setting up a Fetched Results Controller for the Entity named %@", entityName);

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];



    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:nil
                                                                                   cacheName:nil];
    [self.fetchedResultsController performFetch:nil];
}

我没有错误，这里有更多的App Delegate：

- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil)
    {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])
        {
            // Using abort() right now just for development
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        } 
    }
}

#pragma mark - Core Data stack


- (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;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return __managedObjectModel;
}

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

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

    NSError *error = nil;
    __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(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}

#pragma mark - Application's Documents directory


- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

并在我的Model.xcdatamodeid中：

任何帮助都会很棒！谢谢！

Answer 1

以下是方法：

    - (void)setupFetchedResultsController
    {
        NSManagedObjectContext *moc = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription
    entityForName:@"Location" inManagedObjectContext:moc];

NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];

NSError *error = nil;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil)
{
    // Deal with error...
}
else
{
    // your data is in array
}
}

Answer 2

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"FailedBankInfo"
                                          inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (FailedBankInfo *info in fetchedObjects) {
    NSLog(@"Name: %@", info.name);
    FailedBankDetails *details = info.details;
    NSLog(@"Zip: %@", details.zip);
}