Trouble with adding item into an NSMutableArray inside a block

Question

UPDATE: I just found a tricky part... if I do something like this, it works:

[_friendsArrayInBlock insertObject:@"Bla" atIndex:itemIndex];

But it doesn't:

[_friendsArrayInBlock insertObject:friend atIndex:itemIndex];

Why I cannot add a custom object, but I can add NSString? What's the problem

ORIGINAL PART: Here you can see the relevant code part:

@implementation ORGFriendsTableViewController
{
    NSMutableArray *_friendsArray;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    _friendsArray = [NSMutableArray array];
    __block NSMutableArray *_friendsArrayInBlock = _friendsArray;

    [FBRequestConnection startForMyFriendsWithCompletionHandler: ^(FBRequestConnection *connection,
                                                                   id result,
                                                                   NSError *error) {
        FBGraphObject *fbGraphObject = (FBGraphObject *)result;

        NSMutableArray *userArray = fbGraphObject[@"data"];
        for (FBGraphObject *user in userArray) {

            ORGFBUser *friend = [[ORGFBUser alloc] initWithId:user[@"id"] name:user[@"name"] andPhotoURL:@"someurl"];

            NSInteger itemIndex = 0;
            [_friendsArrayInBlock insertObject:friend atIndex:itemIndex];
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForItem:itemIndex inSection:0]] withRowAnimation:UITableViewRowAnimationRight];
        }
    }];
}

The problem appears with on this line:

[_friendsArrayInBlock insertObject:friend atIndex:itemIndex];

Program recieving signal "EXC_BAD_ACCESS"

I think it's related with block concept, and altering a non thread-safe NSMutableArray from it.

Do you have any idea how to fix this?

trojanfoe · Accepted Answer · 2012-12-10 16:36:31Z

3

Blocks can access instance variables without using __block (see this). Therefore this should work:

- (void)viewDidLoad
{
    [super viewDidLoad];

    _friendsArray = [NSMutableArray array];

    [FBRequestConnection startForMyFriendsWithCompletionHandler: ^(FBRequestConnection *connection,
                                                                   id result,
                                                                   NSError *error) {
        FBGraphObject *fbGraphObject = (FBGraphObject *)result;

        NSMutableArray *userArray = fbGraphObject[@"data"];
        for (FBGraphObject *user in userArray) {

            ORGFBUser *friend = [[ORGFBUser alloc] initWithId:user[@"id"] name:user[@"name"] andPhotoURL:@"someurl"];

            NSInteger itemIndex = 0;
            [_friendsArray insertObject:friend atIndex:itemIndex];
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForItem:itemIndex inSection:0]] withRowAnimation:UITableViewRowAnimationRight];
        }
    }];
}

answered Dec 10, 2012 at 16:36

trojanfoe

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2 Comments

newacct Over a year ago

Not only that, but if we wanted to keep _friendsArrayInBlock, he would still not need __block, because he's not assigning to it anywhere.

newacct Over a year ago

Technically, using _friendsArrayInBlock and using _friendsArray directly are different; the former stores the value of _friendsArray at the time the block is created, whereas the latter uses the value when the block is run; though it probably doesn't matter in this case.

Rob · Accepted Answer · 2012-12-10 17:16:19Z

-1

try this

@implementation ORGFriendsTableViewController
{
    NSMutableArray *_friendsArray;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    _friendsArray = [NSMutableArray array];
    __block NSMutableArray *_friendsArrayInBlock = _friendsArray;

    [FBRequestConnection startForMyFriendsWithCompletionHandler: ^(FBRequestConnection *connection,
                                                                   id result,
                                                                   NSError *error) {
        FBGraphObject *fbGraphObject = (FBGraphObject *)result;

        NSMutableArray *userArray = fbGraphObject[@"data"];
        for (FBGraphObject *user in userArray) {

            ORGFBUser *friend = [[ORGFBUser alloc] initWithId:user[@"id"] name:user[@"name"] andPhotoURL:@"someurl"];

            [_friendsArrayInBlock addObject:friend];
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:_friendsArrayInBlock.count-1 inSection:0]] withRowAnimation:UITableViewRowAnimationRight];
        }
    }];
    [self.tableView reloadData];
}

edited Dec 10, 2012 at 17:16

Rob

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answered Dec 10, 2012 at 16:33

Liolik

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2 Comments

Rob Over a year ago

I gather you're replacing insertObject:AtIndex: with addObject? I wish you'd also tell us what you did so we don't have to do our own mental diff in order to figure it out...

Rob Over a year ago

1. The problem the OP describes could not be caused by insertObject, and thus replacing insertObject with addObject will not help, but changes the behavior of the app; 2. I now notice that you're doing reloadData, too, but that's not necessary if you've done insertRowsAtIndexPaths.

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