Core Data: Cannot Access Managed Objects Returned By Fetched Results Controller

I am developing an application for iPad but is unable to display the data already save in core data. I have asked this earlier and many people has helped me but still I am having the same problem. This time, while debugging I am getting the error that the array which I have set up to receive the fetched objects cannot be accessed.

My code is as follows:

    #import "RootViewController.h"
    #import "DetailViewController.h"
    #import "AddViewController.h"
    #import "EmployeeDetailsAppDelegate.h"

/*
 This template does not ensure user interface consistency during editing operations in the table view. You must implement appropriate methods to provide the user experience you require.
 */

@interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end



@implementation RootViewController

@synthesize detailViewController, fetchedResultsController, managedObjectContext, array, dictionary;
//@synthesize array;

#pragma mark -
#pragma mark View lifecycle

- (void)viewDidLoad {

    self.title = @"Employee Name";
    self.navigationItem.rightBarButtonItem = self.editButtonItem;
    [super viewDidLoad];

    if (self.fetchedResultsController) 
    {
        NSArray *tempArr = self.fetchedResultsController.fetchedObjects;
        NSLog(@"temp array is %@",tempArr);
        int count =[tempArr count];
        int i;
        for(i=0;i <count;i++)
        {
            NSManagedObject *category = [tempArr objectAtIndex:i];
            dictionary = [[NSMutableDictionary alloc] initWithCapacity:0];

            if([[category valueForKey:@"EmployeeName"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeName"] forKey:@"EmployeeName"];
            }

            if([[category valueForKey:@"EmployeeID"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeID"] forKey:@"EmployeeID"];
            }
            if([[category valueForKey:@"EmployeeDepartment"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeDepartment"] forKey:@"EmployeeDepartment"];
            }

            [dictionary setObject:[NSNumber numberWithInt:0] forKey:@"EmployeeName"];

        [self.array addObject:dictionary];

        [dictionary release];
        [tempArr release];
        }
    }
}




- (void)viewWillAppear:(BOOL)animated {

    [self.tableView reloadData];
//    [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 {
    // Ensure that the view controller supports rotation and that the split view can therefore show in both portrait and landscape.    
    return YES;
}

#pragma mark -
#pragma mark Add a new object

- (void)insertNewObject:(id)sender {

    AddViewController *add = [[AddViewController alloc]initWithNibName:@"AddViewController" bundle:nil];
    self.modalPresentationStyle = UIModalPresentationFormSheet;
    add.wantsFullScreenLayout = NO;

    [self presentModalViewController:add animated:YES];
    [add release];  
}   


#pragma mark -
#pragma mark Table view data source

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


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

//  id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
//    return [sectionInfo numberOfObjects];
    if([self.array count])
    {
        return [array count];
    }
    return 1;
}


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

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    // Configure the cell.

//  [self configureCell:cell atIndexPath:indexPath];

    if(dictionary = [array objectAtIndex:indexPath.row])
    {
        [dictionary objectForKey:@"EmployeeName"];
        cell.textLabel.text = @"(EmployeeName = %@)";        
    }

    else {
        cell.textLabel.text = @"No Employee Name";
    }


    return cell;
}

-(void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath{

//  AddViewController *detail = [fetchedResultsController objectAtIndexPath:indexPath];
//  cell.textLabel.text = detail.empName.text;
}

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

    if (editingStyle == UITableViewCellEditingStyleDelete) {

        // Delete the managed object.
        NSManagedObject *objectToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
        if (self.detailViewController.detailItem == objectToDelete) {
            self.detailViewController.detailItem = nil;
        }

        NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
        [context deleteObject:[fetchedResultsController objectAtIndexPath:indexPath]];

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


- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
    // The table view should not be re-orderable.
    return NO;
}


#pragma mark -
#pragma mark Table view delegate

- (void)tableView:(UITableView *)aTableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    // Set the detail item in the detail view controller.

    detailViewController = [[DetailViewController alloc]initWithStyle:UITableViewStylePlain];
//  AddViewController *selectedName = (AddViewController *)[[self fetchedResultsController]objectAtIndexPath:indexPath];
//  detailViewController.detail = selectedName;
    [self.navigationController pushViewController:detailViewController animated:YES];
    [detailViewController release];
}


#pragma mark -
#pragma mark Fetched results controller

- (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:@"Details" 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:@"EmployeeName" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    AddViewController *name = [[AddViewController alloc]init];

    if (name.empName.text) {
        NSPredicate *inPredicate = [NSPredicate predicateWithFormat: @"EmployeeName = %@", name.empName.text];
        [fetchRequest setPredicate:inPredicate];
    }

    [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:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptors release];

    return fetchedResultsController;
}    


#pragma mark -
#pragma mark Fetched results controller delegate

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


- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        ca开发者_StackOverflow社区se NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


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

    UITableView *tableView = self.tableView;

    switch(type) {

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


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


#pragma mark -
#pragma mark Memory management

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

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


- (void)viewDidUnload {

    self.fetchedResultsController = nil;
    // Relinquish ownership of anything that can be recreated in viewDidLoad or on demand.
    // For example: self.myOutlet = nil;

//  self.array = nil;
}


- (void)dealloc {

//  [array release];
    [detailViewController release];
    [fetchedResultsController release];
    [managedObjectContext release];

    [super dealloc];
}

@end

---

Firstly, you are needlessly creating an array of dictionaries that does nothing more than duplicate the array already return in fetched results controllers fetchedObjects.

You seem to want to check for null values for managed object attributes but your going about it wrong. This type of check:

if([[category valueForKey:@"EmployeeName"] isKindOfClass:[NSString class]])

... will evaluate as TRUE even if the attribute as no value because value returned by key-value coding will be a string (because of the generated accessor method that always returns a string.

The best place to handle empty fields is in the data model itself. Just set the default value of the attribute EmployeeName to "No Employee Name" and you can dispense with all the checking.

Secondly, you are using inconsistent references to your array. Sometimes you use self.array and other times just array. You will get proper retention only when using the first form. If you use the second, your array may disappear at random.

Thirdly, in tableView:(UITableView *)tableView cellForRowAtIndexPath: this line:

if(dictionary = [array objectAtIndex:indexPath.row])

... uses the wrong access form so it may or may not find the array object. This line:

cell.textLabel.text = @"(EmployeeName = %@)";

... sets all the cell's text to "(EmployeeName =)" and will probably produce a compile error. It should be:

    cell.textLabel.text = [NSString stringWithFormat:@"(EmployeeName = %@)",[dictionary objectForKey:@"EmployeeName"]];

You really should just use the fetched results controller and default fields (as above) like this:

NSManagedObject *mo=[[fetchedResultsController fetchedObjects] objectAtIndex:index.row]];   
    cell.textLabel.text = [NSString stringWithFormat:@"(EmployeeName = %@)",[mo valueForKey:@"EmployeeName"]];

You don't have to do error checking because the number of row in the table always matches the number of fetched managed objects.

I think you are making this a lot more complicated than necessary. You are probably used to doing a lot of integrity checks with data returned by SQL. However, Core Data and the fetched results controller will handle most of that work for you. In a simple setup like this, you usually only have to add about ten lines of code to the tableview controller template.

---

I'm not sure, but I think you the way you are getting the elements to the array fails:

NSArray *tempArr = self.fetchedResultsController.fetchedObjects;

You could try to do a for-loop and add each object into the array. Something like this:

 NSMutableArray *tempArray = [[NSMutableArray alloc] init];

for(elementType *element in [self.fetchedResultsController fetchedObjects])
{
    [tempArray addObject: [element objectForKey: appropriateKey]];
}