Question

Hi i’m fairly new to xcode and i’m having trouble getting my head around why im getting this error “use of undeclared identifier” I’m basically trying to return fetched results to a table view.

//  UNBSearchBooksViewController.m

#import "UNBSearchBooksViewController.h"
#import "NBAppDelegate.h"

@interface UNBSearchBooksViewController ()

@end

@implementation UNBSearchBooksViewController 

@synthesize booksSearchBar;
@synthesize searchTableView;
@synthesize fetchedResultsController, managedObjectContext;

- (void)viewDidLoad
{
    [super viewDidLoad];

    // NSFetchRequest needed by the fetchedResultsController
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    // NSSortDescriptor tells defines how to sort the fetched results
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"title" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    // fetchRequest needs to know what entity to fetch
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"BookInfo" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];   
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return [fetchedObjects count];
}

// Customize the appearance of table view cells.

- (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];
    }

    // Configure the cell "this is where my problem is" use of undeclared identifier
    BookInfo *info = [self.fetchedResultsController objectAtIndexPath:indexPath];

    cell.textLabel.text = info.title;

    return cell;
}


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

}

- (void) searchBarSearchButtonClicked:(UISearchBar *)theSearchBar
{

    if (self.booksSearchBar.text !=nil)
    {
        NSPredicate *predicate =[NSPredicate predicateWithFormat:@"bookName contains[cd] %@", self.booksSearchBar.text];
        [fetchedResultsController.fetchRequest setPredicate:predicate];
    }
    else
    {
        NSPredicate *predicate =[NSPredicate predicateWithFormat:@"All"];
        [fetchedResultsController.fetchRequest setPredicate:predicate];
    }

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error])
    {
        // Handle error
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    }

    fetchedObjects = fetchedResultsController.fetchedObjects;

    [booksSearchBar resignFirstResponder];

    [searchTableView reloadData];   
}

- (void) searchBarTextDidBeginEditing:(UISearchBar *)searchBar
{
    searchBar.showsCancelButton = YES;
}

- (void) searchBarTextDidEndEditing:(UISearchBar *)searchBar

{
    searchBar.showsCancelButton = NO;
}

- (void)searchBarCancelButtonClicked:(UISearchBar *)searchBar
{
    [searchBar resignFirstResponder];
}
- (void)didReceiveMemoryWarning
{

    [super didReceiveMemoryWarning];


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

}
@end

Answer 1

Your problem is that you are assigning to a specific subclass the results typed as a base class. As you stated, this is where you get the warning:

BookInfo *info = [self.fetchedResultsController objectAtIndexPath:indexPath];

‘NSFetchedResultsController’ returns an object of type ‘id’ from

- (id)objectAtIndexPath:(NSIndexPath *)indexPath

(and I suppose it could return a NSManagedObject * too), but you assign it to a BookInfo object. Since there is a mismatch here, you need to cast the return value to what you know it is:

BookInfo *info = (BookInfo *)[self.fetchedResultsController objectAtIndexPath:indexPath];

and your warning will go away.