Changing a managed object property doesn't trigger NSFetchedResu

ghz 7months ago ⋅ 59 views

Changing a managed object property doesn't trigger NSFetchedResultsController to update the table view

I have a fetchedResultsController with a predicate, where "isOpen == YES"

When calling for closeCurrentClockSet, I set that property to NO. Therefore, it should no longer appear on my tableView.

For Some Reason, this is not happening.

Can someone help me figure this out please?

-(void)closeCurrentClockSet
{

    NSPredicate * predicate = [NSPredicate predicateWithFormat:@"isOpen == YES"];

    NSArray *fetchedObjects =
        [self fetchRequestForEntity:@"ClockSet"
                      withPredicate:predicate
             inManagedObjectContext:[myAppDelegate managedObjectContext]];

    ClockSet *currentClockSet = (ClockSet *)fetchedObjects.lastObject;

    [currentClockSet setIsOpen:[NSNumber numberWithBool:NO]];

}

--

I have a couple of methods more, using the exact same approach, by calling a custom fetchRequestForEntity:withPredicate:inManagedObjectContext method.

In those methods, when changing a property, tableView get correctly updated! But this one above (closeCurrentClockSet), doesn't! I can't figure out why.

--

My implementation for my fetchedResultsController, is from Apple's documentation.

Also, another detail. If I send my App, to the background. Close it and re-open, tableView shows updated as it should!

I have tried my best to follow previous questions here on stackOverflow. No luck. I also NSLogged this to the bone. The object is getting correctly fetched. It is the right one. isOpen Property is being correctly updated to NO. But for some reason, my fetchedResultsController doesn't update tableView.

I did try a couple a "hammer" solutions, like reloadData and calling performFetch. But that didn't work. Or would make sense to used them...

EDIT: scratch that, it DID work, calling reloadData imediatly after performFetch on my resultsController but using reloadData is hammering a solution. Plus, it takes out all animations. I want my controller to auto-update my tableView.

Can someone help me figure this out?

Any help is greatly appreciated!

Thank you,

Nuno

EDIT:

The complete implementation.

fetchedResultsController is pretty standard and straightforward. Everything else is from Apple's documentation

- (NSFetchedResultsController *)fetchedResultsController
{

    if (_fetchedResultsController) {
        return _fetchedResultsController;
    }

    NSManagedObjectContext * managedObjectContext = [myAppDelegate managedObjectContext];

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

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        [fetchRequest setEntity:entity];

    NSString *predicate = [NSString stringWithFormat: @"clockSet.isOpen == YES"];
        [fetchRequest setPredicate: [NSPredicate predicateWithFormat:predicate]];

    NSSortDescriptor *sortDescriptor1 =
        [[NSSortDescriptor alloc] initWithKey:@"clockIn" ascending:NO];

    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, nil];

        [fetchRequest setSortDescriptors:sortDescriptors];
        [fetchRequest setFetchBatchSize:20];

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


    _fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;

}

--

Boilerplate code from Apple's documentation:

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    // The fetch controller is about to start sending change notifications, so prepare the table view for updates.
    [self.tableView beginUpdates];
}



- (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:UITableViewRowAnimationTop];

            break;

        case NSFetchedResultsChangeDelete:

            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];

            break;

        case NSFetchedResultsChangeUpdate:

            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];

            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationFade];

            break;

        case NSFetchedResultsChangeMove:

            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationLeft];

            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationTop];

            break;
    }
}



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

    UITableView *tableView = self.tableView;

    switch(type) {

        case NSFetchedResultsChangeInsert:

            [tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex]
                     withRowAnimation:UITableViewRowAnimationFade];

            break;

        case NSFetchedResultsChangeDelete:

            [tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex]
                     withRowAnimation:UITableViewRowAnimationFade];

            break;
    }
}



- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    // The fetch controller has sent all current change notifications, so tell the table view to process all updates.
    [self.tableView endUpdates];
}

1ST UPDATE:

Tracking [managedObjectContext hasChanges] does return YES, as it should. But fetchedResultsController doesn't update the tableView

2ND UPDATE

didChangeObject:atIndexPath: does not get called for this particular case! I have 2 more methods, with the EXACT same code, they just happen to be a different entity. And they work perfectly. Thank you @Leonardo for pointing this out

3TH UPDATE this method, follows the same rules. But does actually work.

- (void)clockOut
{
    NSPredicate * predicate = [NSPredicate predicateWithFormat:@"isOpen == %@", [NSNumber numberWithBool:YES]];

    NSArray * fetchedObjects =
        [self fetchRequestForEntity:@"ClockPair"
                      withPredicate:predicate
             inManagedObjectContext:[myAppDelegate managedObjectContext]];

    ClockPair *aClockPair = (ClockPair *)fetchedObjects.lastObject;

    aClockPair.clockOut = [NSDate date];
    aClockPair.isOpen   = [NSNumber numberWithBool:NO];


}

Anyone has any other ideas for what I might be missing?

Thank you,

Answers

To ensure your NSFetchedResultsController correctly updates the UITableView when changes occur, especially when setting a property to exclude an object from the fetched results, it's crucial to properly handle the managed object context's save operation and the fetched results controller's delegate methods.

Steps to Ensure Updates

  1. Save the Managed Object Context: Make sure you save the managed object context after making changes. If the context is not saved, changes won't be persisted, and the fetched results controller won't be notified of updates.

  2. Verify the Fetched Results Controller's Delegate: Ensure that the fetched results controller's delegate methods are properly set up and that controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: is being called.

  3. Check the Fetch Predicate: Ensure the predicate used by the fetched results controller is correctly set to match the updated conditions.

Revised Code Example

Here's a revised approach incorporating these points:

Save the Managed Object Context

After updating the isOpen property, save the context:

-(void)closeCurrentClockSet {
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"isOpen == YES"];
    NSArray *fetchedObjects = [self fetchRequestForEntity:@"ClockSet"
                                            withPredicate:predicate
                                   inManagedObjectContext:[myAppDelegate managedObjectContext]];

    ClockSet *currentClockSet = (ClockSet *)fetchedObjects.lastObject;
    currentClockSet.isOpen = @NO;

    NSError *error = nil;
    if (![[myAppDelegate managedObjectContext] save:&error]) {
        NSLog(@"Failed to save context: %@", error);
    }
}

Ensure Delegate Methods Are Called

Double-check that your fetched results controller's delegate methods are correctly implemented and that they handle all possible changes.

Here’s the full delegate implementation again for reference:

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

- (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:@[newIndexPath] withRowAnimation:UITableViewRowAnimationTop];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeUpdate:
            [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationTop];
            break;
    }
}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id<NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type {
    UITableView *tableView = self.tableView;
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

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

Ensure Predicate Accuracy

Ensure that the predicate used by the fetched results controller matches the expected logic. For example:

- (NSFetchedResultsController *)fetchedResultsController {
    if (_fetchedResultsController) {
        return _fetchedResultsController;
    }

    NSManagedObjectContext *managedObjectContext = [myAppDelegate managedObjectContext];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"ClockPair" inManagedObjectContext:managedObjectContext];

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setEntity:entity];

    NSString *predicate = @"clockSet.isOpen == YES";
    [fetchRequest setPredicate:[NSPredicate predicateWithFormat:predicate]];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"clockIn" ascending:NO];
    [fetchRequest setSortDescriptors:@[sortDescriptor]];
    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                                                 managedObjectContext:managedObjectContext
                                                                                                   sectionNameKeyPath:nil
                                                                                                            cacheName:@"Root"];
    _fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;
}

Conclusion

By ensuring the context is saved after updates, verifying the delegate methods are correctly implemented, and checking that predicates are accurate, you can make sure the NSFetchedResultsController properly updates your UITableView. This should resolve the issue of the table view not reflecting changes when isOpen is set to NO.

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