NSFetchresultController

@sandris · March 2012

Hi!
I'd like to search in my core data project with predicate.
So I created this code:

- (NSFetchedResultsController *)fetchedResultsController {
    NSLog(@\"Fethrequest\");
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    //Fetch request
    CoreData_SzotarAppDelegate *coreData = [[UIApplication sharedApplication] delegate];
    
    NSManagedObjectContext *context = coreData.managedObjectContext;
    fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@\"Data\" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    if (magyar.isFirstResponder == YES) {
        predicate = [NSPredicate predicateWithFormat:@\"magyarszo contain %@\", magyar.text];
        [fetchRequest setPredicate:predicate];
        
        NSError *error = nil;
        NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
        if (fetchedObjects == nil) {
        }

    }
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@\"datum\"
                                                                       ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
    
    [fetchRequest setFetchBatchSize:20];
    
    NSFetchedResultsController *theFetchedResultsController = 
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                        managedObjectContext:context sectionNameKeyPath:nil 
                                                   cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;
    
    [theFetchedResultsController release];
    [fetchRequest release];
    
    return _fetchedResultsController;    
}

But it doesn't update the predicate so how can i update it?
What can I do?
Thank for your answer

BrianSlick · March 2012

You only set the predicate here:

if (magyar.isFirstResponder == YES) {
        predicate = [NSPredicate predicateWithFormat:@\"magyarszo contain %@\", magyar.text];
        [fetchRequest setPredicate:predicate];
        
        NSError *error = nil;
        NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
        if (fetchedObjects == nil) {
        }

    }

...so if that isn't running, then isn't it really rather obvious that magyar is not the first responder?

@sandris · March 2012

Yes i got it. but when I running the app the search bar (= magyar.text) is not first responder just became when I tapped on them and now the fetchedResultsController don't recognize that so don't update the predicate because

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

here return to _fetchedResultsController and don't execute the code what under that.
So how can I do to recognize when the firstResponder the searchBar if the
_fetchedResultsController != nil and execute the predicate

BrianSlick · March 2012

Set the FRC to nil when you activate the search bar.

@sandris · March 2012

When I set to nil the FRC is not update the tableView so should I set back the FRC != nil?

BrianSlick · March 2012

That is a lazy-loading getter. The FRC will be automatically recreated the next time you ask for it. If you need the table to reload, then reload it.

@sandris · March 2012

BrianSlick;421108 said:
That is a lazy-loading getter. The FRC will be automatically recreated the next time you ask for it. If you need the table to reload, then reload it.

Thanks for your all answers. The last question: How can I ask the FRC to recreate.

BrianSlick · March 2012

Do you understand what that code does?

@sandris · March 2012

BrianSlick;421151 said:
Do you understand what that code does?

Yes I do it atumaticaly update the tableview when the context change but i change the predicate(insert into the fetchrequest) but the fetchresult is not change (set to nil and bulid and execute the predicate but nothing)

BrianSlick · March 2012

Post code to show what you are doing.

@sandris · March 2012

I just like to make an simple list in a tableView what is sorted(can sorted by different conditions),search in the list(I think with the predicate) and I can add items to the list, all of that in runtime.

- (NSFetchedResultsController *)fetchedResultsController {
    NSLog(@\"Fethrequest\");
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    //Fetch request
    CoreData_SzotarAppDelegate *coreData = [[UIApplication sharedApplication] delegate];
    
    NSManagedObjectContext *context = coreData.managedObjectContext;
    fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@\"Data\" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    if (magyar.isFirstResponder == YES) {
        predicate = [NSPredicate predicateWithFormat:@\"magyarszo contain %@\", magyar.text];
        [fetchRequest setPredicate:predicate];
        
        NSError *error = nil;
        NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
        if (fetchedObjects == nil) {
        }

    }
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@\"datum\"
                                                                       ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
    
    [fetchRequest setFetchBatchSize:20];
    
    NSFetchedResultsController *theFetchedResultsController = 
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                        managedObjectContext:context sectionNameKeyPath:nil 
                                                   cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;
    
    [theFetchedResultsController release];
    [fetchRequest release];
    
    return _fetchedResultsController;    
}

At the start I sorted the loaded list, and then I would like to search(magyar.text became firstResponder, i tap that) and if I haven't got any matches I would add the value(what I write to the searchBar) to the list.

-(void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText{
    _fetchedResultsController  = nil;
    [self fetchedResultsController];
   }

I made this to check is the magyar.text firstResponder and FRC set to nil to predicate can executed, but when FRC = nil I can't add items to thee list (and the predicate doesn't work I don't know why)

BrianSlick · March 2012

You have to tell a FRC to perform the fetch. You aren't doing that anywhere.

And you are leaking the FRC. Use the property.

@sandris · April 2012

BrianSlick;421330 said:
You have to tell a FRC to perform the fetch. You aren't doing that anywhere.

And you are leaking the FRC. Use the property.

How can I tell a FRC to perform the Fetch. How works this. Can you suggest a good tutorial for this.

BrianSlick · April 2012

Pro Core Data for iOS, Second Edition

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