核心数据应用不会从持久性存储中加载数据

Question

I've any problems for app I'm developing...
I'm using Core Data and I just write initial code...
But one of my problem is: Core Data won't load data stored in persistent store...
This is my code!

MyWishesAppDelegate.h

#import UIKit/UIKit.h
#import CoreData/CoreData.h

@interface MyWishesAppDelegate : NSObject  {

    UIWindow *window;
 UITabBarController *tabBarController;

@private
    NSManagedObjectContext *managedObjectContext_;
    NSManagedObjectModel *managedObjectModel_;
    NSPersistentStoreCoordinator *persistentStoreCoordinator_;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UITabBarController *tabBarController;

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

- (NSString *)applicationDocumentsDirectory;

@end

MyWishesAppDelegate.m

#import "MyWishesAppDelegate.h"


@implementation MyWishesAppDelegate

@synthesize window;
@synthesize tabBarController;


#pragma mark -
#pragma mark Application lifecycle

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.
 [window insertSubview:tabBarController.view atIndex:0];
    [window makeKeyAndVisible];

 return YES;
}


- (void)applicationWillResignActive:(UIApplication *)application {
    /*
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions
  (such as an incoming phone call or SMS message)
  or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
     */
}


- (void)applicationDidEnterBackground:(UIApplication *)application {
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application
  to its current state in case it is terminated later. 
     If your application supports background execution, called instead of applicationWillTerminate: when the user quits.
     */
}


- (void)applicationWillEnterForeground:(UIApplication *)application {
    /*
     Called as part of  transition from the background to the inactive state: here you can undo many of the changes made on entering the background.
     */
}


- (void)applicationDidBecomeActive:(UIApplication *)application {
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background,
  optionally refresh the user interface.
     */
}


- (void)applicationWillTerminate:(UIApplication *)application {

    NSError *error = nil;
    if (managedObjectContext_ != nil) {
        if ([managedObjectContext_ hasChanges] && ![managedObjectContext_ save:&error]) {

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


#pragma mark -
#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_;
    }
    NSString *modelPath = [[NSBundle mainBundle] pathForResource:@"MyWishes" ofType:@"momd"];
    NSURL *modelURL = [NSURL fileURLWithPath:modelPath];
    managedObjectModel_ = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL]; 

    return managedObjectModel_;
}


- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (persistentStoreCoordinator_ != nil) {
        return persistentStoreCoordinator_;
    }

    NSURL *storeURL = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"MyWishes.sqlite"]];

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

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

    return persistentStoreCoordinator_;
}


#pragma mark -
#pragma mark Application's Documents directory

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


#pragma mark -
#pragma mark Memory management

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
}


- (void)dealloc {

    [managedObjectContext_ release];
    [managedObjectModel_ release];
    [persistentStoreCoordinator_ release];

 [tabBarController release];
    [window release];
    [super dealloc];
}


@end

WishlistViewController.h

#import UIKit/UIKit.h
#import CoreData/CoreData.h

@interface WishlistViewController : UITableViewController  {

@private
 NSFetchedResultsController *_fetchedResultsController;

}

@property (nonatomic, readonly) NSFetchedResultsController *fetchedResultsController;

-(void)add;
-(IBAction)edit;

@end

WishlistViewController.m

#import "WishlistViewController.h"
#import "MyWishesAppDelegate.h"

@implementation WishlistViewController

@synthesize fetchedResultsController = _fetchedResultsController;

#pragma mark -
#pragma mark Actions

-(void)add {
 NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
 NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
 NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];

 NSError *error;
 if (![context save:&error])
  NSLog(@"Error saving entity: %@", [error localizedDescription]);

 // TODO: instantiate detail editing controller and push onto stack
}

-(IBAction)edit {
 BOOL editing = !self.tableView.editing;
 self.navigationItem.rightBarButtonItem.enabled = !editing;
 self.navigationItem.leftBarButtonItem.title = (editing) ? (@"Done") : (@"Edit");
 [self.tableView setEditing:editing animated:YES];
}

#pragma mark -
#pragma mark View lifecycle

-(void)viewDidLoad {
 [super viewDidLoad];
 NSError *error = nil;
 if (![[self fetchedResultsController] performFetch:&error]) {
  UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Errore caricamento dati"
              message:[NSString stringWithFormat:@"L'errore è stato: %@", [error localizedDescription]]
                delegate:self
             cancelButtonTitle:@"Ok!"
             otherButtonTitles:nil];
  [alert show];
 }
}

-(void)viewDidAppear:(BOOL)animated {
 UIBarButtonItem *editButton = self.editButtonItem;
 [editButton setTarget:self];
 [editButton setAction:@selector(edit)];
 self.navigationItem.leftBarButtonItem = editButton;

 UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
                      target:self
                      action:@selector(add)];
 self.navigationItem.rightBarButtonItem = addButton;
 [addButton release];
}

#pragma mark -
#pragma mark Memory management

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (void)viewDidUnload {
}

- (void)dealloc {
 [_fetchedResultsController release];
    [super dealloc];
}

#pragma mark -
#pragma mark Table View Methods

-(NSInteger)numberOfSectionsInTableView:(UITableView *)theTableView {
 NSUInteger count = [[self.fetchedResultsController sections] count];
 if (count == 0) {
  count = 1;
 }
 return count;
}

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
 NSArray *sections = [self.fetchedResultsController sections];
 NSUInteger count = 0;
 if ([sections count]) {
  id  sectionInfo = [sections objectAtIndex:section];
  count = [sectionInfo numberOfObjects];
 }
 return count;
}

-(UITableViewCell *)tableView:(UITableView *)theTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

 static NSString *WishlistTableViewCell = @"WishlistTableViewCell";

 UITableViewCell *cell = [theTableView dequeueReusableCellWithIdentifier:WishlistTableViewCell];
 if (cell == nil) {
  cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:WishlistTableViewCell] autorelease];
 }

 NSManagedObject *oneWish = [self.fetchedResultsController objectAtIndexPath:indexPath];
 cell.textLabel.text = [oneWish valueForKey:@"nome"];

 /*UIImageView *cellBg = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"cellBg.png"]];
 cell.backgroundView = cellBg;*/
 /*cell.detailTextLabel.text = [oneWish valueForKey:@"costo"];*/

 return cell;
}

-(void)tableView:(UITableView *)theTableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
 // TODO: instantiate detail editing view controller and push onto stack
}

-(void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {

 if (editingStyle == UITableViewCellEditingStyleDelete) {
  NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
  [context deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]];

  NSError *error;
  if (![context save:&error]) {
   NSLog(@"Errore non risolto: %@, %@", error, [error userInfo]);
   UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Errore salvataggio dati"
               message:@"Impossibile salvare dopo aver cancellato un elemento"
                 delegate:self
              cancelButtonTitle:@"Ok!"
              otherButtonTitles:nil];
   [alert show];
  }
 }
}

#pragma mark -
#pragma mark Fetched Results Controller

-(NSFetchedResultsController *)fetchedResultsController {

 if (_fetchedResultsController != nil) {
  return _fetchedResultsController;
 }

 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
 MyWishesAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
 NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;

 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Wish" inManagedObjectContext:managedObjectContext];

 NSString *sectionKey = nil;
 NSSortDescriptor *sortByName = [[NSSortDescriptor alloc] initWithKey:@"nome" ascending:YES];
 NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByName, nil];
 [fetchRequest setSortDescriptors:sortDescriptors];
 [sortByName release];
 [sortDescriptors release];
 sectionKey = @"nome";

 [fetchRequest setEntity:entity];
 [fetchRequest setFetchBatchSize:20];

 NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                    managedObjectContext:managedObjectContext
                   sectionNameKeyPath:sectionKey
                      cacheName:@"Wish"];
 frc.delegate = self;
 _fetchedResultsController = frc;
 [fetchRequest release];

 return _fetchedResultsController;
}

-(void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
 [self.tableView beginUpdates];
}

-(void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
 [self.tableView endUpdates];
}

-(void)controller:(NSFetchedResultsController *)controller
  didChangeObject:(id)anObject
   atIndexPath:(NSIndexPath *)indexPath
 forChangeType:(NSFetchedResultsChangeType)type
  newIndexPath:(NSIndexPath *)newIndexPath {

 switch(type) {
  case NSFetchedResultsChangeInsert:
   [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
   break;
  case NSFetchedResultsChangeDelete:
   [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
   break;
  case NSFetchedResultsChangeUpdate: {
   NSString *sectionKeyPath = [controller sectionNameKeyPath];
   if (sectionKeyPath == nil)
    break;
   NSManagedObject *changedObject = [controller objectAtIndexPath:indexPath];
   NSArray *keyParts = [sectionKeyPath componentsSeparatedByString:@"."];
   id currentKeyValue = [changedObject valueForKeyPath:sectionKeyPath];
   for (int i = 0; i )sectionInfo
    atIndex:(NSUInteger)sectionIndex
 forChangeType:(NSFetchedResultsChangeType)type {

 switch(type) {
  case NSFetchedResultsChangeInsert:
   if (!(sectionIndex == 0 && [self.tableView numberOfSections] == 1) && [self.tableView numberOfRowsInSection:0] == 0)
    [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
   break;
  case NSFetchedResultsChangeDelete:
   if (!(sectionIndex == 0 && [self.tableView numberOfSections] == 1) && [self.tableView numberOfRowsInSection:0] == 0)
    [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
   break;
  case NSFetchedResultsChangeMove:
   break;
  case NSFetchedResultsChangeUpdate:
   break;
  default:
   break;
 }
}

#pragma mark -
#pragma mark Alert View Delegate

-(void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex {
 exit(-1);
}


@end

Anyone can help me? If there are other problems in this code, you can say it to me...

Answer 1

Check the value returned by

#pragma mark Application's Documents directory

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

I believe this should be:

- (NSString *)applicationDocumentsDirectory {
    return [(NSArray *)NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
} 

Answer 2

Start off by running in the debugger with a breakpoint on objc_exception_throw which will cause your app to stop just before it crashes so you can see what the offending line of code is. That will tell you what is causing the problem.