Creating UIImage array

Question

I've written code that gathers images from JSON requests and attempts to add them to an NSMutableArray to be used later in a table view. The problem is after adding the image objects to the array, the size of my NSMutableArray is 0. Here is the relevant code:

@implementation example{
    NSMutableArray *_placeImages;
}

-(void)viewDidLoad{
    ...
    _placeImages = [[NSMutableArray alloc] init];
}

-(void)JsonQuery {
    ...
    // Retrieve the results of the URL.
    dispatch_async(kMyQueue, ^{
    [self downloadImages];
    [self performSelectorOnMainThread:@selector(reloadTableData) withObject:NULL waitUntilDone:YES];
    });
}

-(void)downloadImages{
     ...
     NSData* data = [NSData dataWithContentsOfURL: url];
    UIImage* image = [UIImage imageWithData:data];
    [_placeImages addObject:image];
}

Have you initialized your array anywhere? _placeImages = [NSMutableArray new] — Mike S
– Mike S, Commented Aug 19, 2014 at 1:51
Yes! I forgot to add that bit, but I do [[NSMutableArray alloc] init]. I wonder if it has to do with accessing the array from another thread. — lazarus
– lazarus, Commented Aug 19, 2014 at 23:19
Regardless your current problem, what you did here is not a correct way to collect and show images. I suggest you should use SDWebImage for images to show on UITableView. It is easy to deploy and use. Almost everyone use it for UITableView + Image combo. It has own caching mechanism, you do not need to download same images again and again. — modusCell
– modusCell, Commented Aug 19, 2014 at 23:34
@SevP Are you sure viewDidLoad is firing before downloadImages? — Mike S
– Mike S, Commented Aug 20, 2014 at 2:11
Yes. I've also tried alloc/init immediately before adding objects. It must've been something else buried in my code, too much too paste here. I ended up using @mohacs suggestion which completely voided the question. Thanks for the help! — lazarus
– lazarus, Commented Aug 21, 2014 at 8:09

Tran Quan · Accepted Answer · 2014-08-19 02:12:30Z

3

you must alloc NSMutableArray first:

_placeImages = [[NSMutableArray alloc] init];

or you can using lazy init:

- (NSMutableArray *)placeImages
{
    if (!_placeImages) {
       _placeImages = [[NSMutableArray alloc] init];
    }
    return _placeImages
}

answered Aug 19, 2014 at 2:12

Tran Quan

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2 Comments

lazarus Over a year ago

Thanks for the response. I actually do alloc and init in my viewDidLoad method, but this would certainly have been an issue.

Tran Quan Over a year ago

If it not necessary to use NSMutableAarray, I recommend you using NSArray, because NSMutableArray have no thread safe. Beside, declare _placeImages as property, using lazy init and only access it with self.placeImages. Hope this can help u, good luck.

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