Adding object to NSMutableArray works just for the first time

Question

In my app I have a method that, when I press a button, adds a string to a NSMutableArray which is the model for a UITableView.

 - (void)addPressed:(id)sender
{
    NSString *string = @"aString";
    [self.array addObject:string];
    NSLog(@"Array count: %d",[self.array count]);
    [self.tableView reloadData];
}

Problem is that the adding works the first time only if I press twice the button connected to this action I get this output:

2012-09-16 21:33:08.766 iUni[3066:c07] Array count: 1 //Which is fine since it worked
2012-09-16 21:33:08.952 iUni[3066:c07] Array count: 1 //Now count should be 2!!

Anyone has a guess on why is this happening?

I added the @property, synthesized it and lazy instatiated it this way:

- (NSMutableArray *)array
{
    if (!_array) {
        NSMutableArray *array = [NSMutableArray array];
        _array = array;
    }
    return _array;
}

WHat is the actual content of your array? How is your array declared and initiated? You should log self.array directly instead of its count property. — AliSoftware
– AliSoftware, Commented Sep 16, 2012 at 19:45
Have been starring this question for a minute or two but still don't see its relation to Xcode... — user529758
– user529758, Commented Sep 16, 2012 at 19:48
At the moment of the first adding array is empty. I declared it as a property, then I synthesized it and then I laze instatiated it in its getter. — BigLex
– BigLex, Commented Sep 16, 2012 at 19:51
@H2CO3 Since I am developing an iPhone app in Xcode and this code is related to that app I thought that tagging it with Xcode wasn't wrong.. If it is, my bad! I'll remove the tag! P.S. I'm sorry if there are mistakes but I'm not english — BigLex
– BigLex, Commented Sep 16, 2012 at 19:55
@H2CO3 Fine fine I removed it please don't kill me XD Just Joking, thanks for correcting me ;) — BigLex
– BigLex, Commented Sep 16, 2012 at 19:58

jscs · Accepted Answer · 2012-09-16 20:07:01Z

3

Your array is being created as an unowned (autoreleased, actually) object, which means that it is destroyed shortly after each time your accessor is called. It is then recreated the next time you access it, which gives you a new, empty array.

You need to create an owned version of the array to store into your instance variable:

if (!_array) {
    _array = [[NSMutableArray alloc] init];
    // Note no need to create a temp variable.
}
return _array;

You could also turn on ARC, which would have taken care of this for you and is a good idea anyways.

answered Sep 16, 2012 at 20:07

jscs

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1 Comment

Cfr Over a year ago

btw, you can do [NSMutableArray new] instead of [[... alloc] init]

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