Question

I’m new to iOS, so apologies if this is brain dead simple… I’ve been iteratively working through some small proof of concept apps before starting to implement my full app so that it wouldn’t be as overwhelming. I had my table view working fine when I created it following the “Your Second iOS App” tutorial on the Apple website. Now I’ve tried creating it in a tab bar app though, and I’m seeing problems with the NSFetchedResultsController, and I’m not sure if it’s related to something that I’m doing wrong in the Storyboard, or something else.

I have a Tab Bar Controller that connects to a Table View Controller (CatalogViewController.h/m) that is embedded in a Navigation Controller. The Table View Controller is configured to have static cells. In the first static cell I have a push segue to another Table View Controller (FoodCatalogViewController.h/m) which is configured to use dynamic prototypes – this is the view in which I expect to see the objects from my database (from the Food entity – currently just shows name and calories). This view has an “Add” button to create new entries in the database – the add button has a modal segue to another static table view (AddFoodViewController.h/m) that is embedded in it’s own navigation controller. I know that the “Add” button is working and that it’s view is correctly connecting to the database (i.e. I’m passing/setting the NSManagedObjectContext correctly), because if I open the app’s sqlite database file using “SQLite Database Browser”, I see the items that I’ve added in the simulator. I just don’t understand why they’re not getting displayed in my table view via the NSFetchedResultsController. I stepped through the code using breakpoints and confirmed that the performFetch code is being called in my FoodCatalogViewController’s fetchedResultsController function. I added a debug NSLog line in the numberOfRowsInSection code, and it seems to be nil, so I never get into cellForRowAtIndexPath or configureCell. So it looks like the NSFetchedResultsController is the culprit – I just don’t know why it’s not fetching the results correctly, and what I can do to debug this further. Can anyone help me with this?

In order to pass the Core Data info through the hierarchy, I have the following code snippets:

AppDelegate.m:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    UITabBarController *tabBarController = (UITabBarController *)self.window.rootViewController;

    // Setup the Catalogs Tab
    UINavigationController *navigationController = [[tabBarController viewControllers] objectAtIndex:0];
    CatalogViewController *catalogViewController = [[navigationController viewControllers] objectAtIndex:0];
    catalogViewController.managedObjectContext = self.managedObjectContext;
    return YES;
}

CatalogViewController.m (the first table view controller in the sequence – I pass the NSManagedObjectContext through to it):

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:@"BrowseFoodCatalog"]) {        
        [[segue destinationViewController] setManagedObjectContext:self.managedObjectContext];
    }
}

FoodCatalogViewController.h (the second table view controller in the sequence – I use the NSManagedObjectContext to setup the NSFetchedResultsController):

@interface FoodCatalogViewController : UITableViewController <NSFetchedResultsControllerDelegate>

@property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;

- (void) addFoodWithName:(NSString *)name calories:(NSNumber *)calories;

@end

FoodCatalogViewController.m (the second table view controller in the sequence – I use the NSManagedObjectContext to setup the NSFetchedResultsController):

@interface FoodCatalogViewController () <AddFoodViewControllerDelegate>
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end

@implementation FoodCatalogViewController

@synthesize fetchedResultsController = __fetchedResultsController;
@synthesize managedObjectContext = __managedObjectContext;


- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    // Set up the fetched results controller.
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Food" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
}    


- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[self.fetchedResultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo numberOfObjects];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"FoodCell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    [self configureCell:cell atIndexPath:indexPath];
    return cell;
}

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = [[managedObject valueForKey:@"name"] description];
    NSNumber *calorieNum = [managedObject valueForKey:@"calories"];
    cell.detailTextLabel.text = [[calorieNum stringValue] description];
}

Additional Info
Not sure if this is relevant, but in order to get CoreData to automatically be included in my project, I started with the Single View template, but modified it’s TemplateInfo.plist to add the following line under the similar line for storyboarding:

<string>com.apple.dt.unit.coreDataCocoaTouchApplication</string>

I’d found this online somewhere in someone’s forum or something. Could this have messed up the CoreData somehow?

Additional Code
As requested, here’s the code that I use to add new elements to the database:

AddFoodViewController.h:

#import <UIKit/UIKit.h>
@protocol AddFoodViewControllerDelegate;

@interface AddFoodViewController : UITableViewController <UITextFieldDelegate>
@property (weak, nonatomic) IBOutlet UITextField *foodNameInput;
@property (weak, nonatomic) IBOutlet UITextField *caloriesInput;
@property (weak, nonatomic) id <AddFoodViewControllerDelegate> delegate;

- (IBAction)save:(id)sender;
- (IBAction)cancel:(id)sender;

@end

@protocol AddFoodViewControllerDelegate <NSObject>
- (void)addFoodViewControllerDidCancel:(AddFoodViewController *)controller;
- (void)addFoodViewControllerDidSave:(AddFoodViewController *)controller name:(NSString *)name calories:(NSNumber *)calories;
@end

AddFoodViewController.m:

#import "AddFoodViewController.h"

@implementation AddFoodViewController
@synthesize foodNameInput;
@synthesize caloriesInput;
@synthesize delegate = _delegate;

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
}

- (void)viewDidUnload
{
    [self setFoodNameInput:nil];
    [self setCaloriesInput:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    if ((textField == self.foodNameInput) || (textField == self.caloriesInput )) {
        [textField resignFirstResponder];
    }
    return YES;
}

- (IBAction)save:(id)sender {
    int caloriesInt = [self.caloriesInput.text intValue];
    NSNumber *caloriesNum = [NSNumber numberWithInt:caloriesInt];
    [[self delegate] addFoodViewControllerDidSave:self name:self.foodNameInput.text calories:caloriesNum];
}

- (IBAction)cancel:(id)sender {
    [[self delegate] addFoodViewControllerDidCancel:self];
}
@end

FoodCatalogViewController.m (the AddFoodViewControllerDelegate protocol code to add to the database):

- (void)addFoodViewControllerDidCancel:(AddFoodViewController *)controller {
    [self dismissViewControllerAnimated:YES completion:NULL];
}

- (void)addFoodViewControllerDidSave:(AddFoodViewController *)controller name:(NSString *)name calories:(NSNumber *)calories {
    if ([name length]) {
        [self addFoodWithName:name calories:calories];
        [[self tableView] reloadData];
    }
    [self dismissModalViewControllerAnimated:YES];
}

- (void) addFoodWithName:(NSString *)name calories:(NSNumber *)calories {
    // Create a new instance of the entity managed by the fetched results controller.
    NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
    NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
    NSLog(@"entity name is %@", [entity name]);
    NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];

    // If appropriate, configure the new managed object.
    // Normally you should use accessor methods, but using KVC here avoids the need to add a custom class to the template.
    [newManagedObject setValue:name forKey:@"name"];
    [newManagedObject setValue:calories forKey:@"calories"];
    CFUUIDRef uuidRef = CFUUIDCreate(NULL);
    CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
    NSString* uuid = [NSString stringWithString:(__bridge NSString *)uuidStringRef];
    [newManagedObject setValue:uuid forKey:@"uuid"];

    // Save the context.
    NSError *error = nil;
    if (![context save:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }   
}

More Debug Info
Strange – it looks like the fetchedResultsController isn’t working correctly in the FoodCatalogViewController even though the managedObjectContext seems to be working… Here’s the modified fetchedResultsController function from FoodCatalogViewController.m with some debug NSLog statements and replacing self.fetchedResultsController with __fetchedResultsController (because I wondered if that was causing the problem).

Here’s the output from the fetchedResultsController function NSLog calls:

2012-01-29 10:22:21.118 UltraTrack[19294:fb03] Result: (
    "<Food: 0x6e651b0> (entity: Food; id: 0x6e64630 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p1> ; data: <fault>)",
    "<Food: 0x6e653e0> (entity: Food; id: 0x6e61870 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p3> ; data: <fault>)",
    "<Food: 0x6e65450> (entity: Food; id: 0x6e64420 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p4> ; data: <fault>)",
    "<Food: 0x6e654c0> (entity: Food; id: 0x6e64430 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p5> ; data: <fault>)",
    "<Food: 0x6e65530> (entity: Food; id: 0x6e64e80 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p2> ; data: <fault>)",
    "<Food: 0x6e655b0> (entity: Food; id: 0x6e64e90 <x-coredata://8A10B827-9F10-4760-934C-0061A982B73C/Food/p6> ; data: <fault>)"
)
2012-01-29 10:22:21.907 UltraTrack[19294:fb03] Number or objects: 6

And here’s the modified fetchedResultsController function:

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    // Set up the fetched results controller.
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Food" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];
    aFetchedResultsController.delegate = self;
    __fetchedResultsController = aFetchedResultsController;

    NSArray *result = [self.managedObjectContext executeFetchRequest:fetchRequest error:nil];
    NSLog(@"Result: %@", result);

    NSError *error = nil;
    if (![__fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    NSLog(@"Number or objects: %d", [__fetchedResultsController.fetchedObjects count]);

    return __fetchedResultsController;
}

Someone suggested that the sections were the problem, so I hard-coded numberOfSectionsInTableView to return 1, and then the first object from the fetchResults seems to be handled correctly, but I get the following exception:

2012-01-29 10:29:27.296 UltraTrack[19370:fb03] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no object at index 1 in section at index 0'

If I hardcode numberOfRowsInSection to also return 1, then the first object from my database is correctly displayed in the table view. What could be the problem with regard to the sections info in the fetchedResultsController? Could I have setup something incorrectly in the storyboard for the table view with regard to sections?

Here’s the 2 table view functions where I’ve tried the hard-coding:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
    //NSLog(@"Number of sections in table view is %d", [[self.fetchedResultsController sections] count]);
    //return [[self.fetchedResultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSLog(@"Number or objects: %d", [self.fetchedResultsController.fetchedObjects count]);
    // If I return 1, the object is displayed correctly, if I return count, I get the exception
    //return 1;
    return [self.fetchedResultsController.fetchedObjects count];

    // Return the number of rows in the section.
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    NSLog(@"Number of rows being returned is %d", [sectionInfo numberOfObjects]);
    return [sectionInfo numberOfObjects];
}

Answer 1

From your description it seems that the code with the sections is the culprit. But you are not actually using any sections. So try this to simplify:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [self.fetchedResultsController.fetchedObjects count];
}

If this still returns zero rows, check your fetchedObjects.count in the fetchedResultsController getter method.