JSON File Not Loading until UITableView

Question

In order to test my App I have created a JSON file that I am drawing fake values from, however in my table View I want to exclude the user's data. In order to load this file I have used this code:

//create a new JSONLoader with a local file from URL
JSONLoader *jsonLoader = [[JSONLoader alloc] init];
NSURL *url = [[NSBundle mainBundle] URLForResource:@"chatters" withExtension:@"json"];
//load the data on a background queue
//use for when connecting a real URL
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                                                                        _localChatters =    [jsonLoader chattersFromJSONFile:url];
                                                                        //push data on   main thread (reload table view once JSON has arrived)
                                                                           //[self.tableView performSelectorOnMainThread:@selector(reloadData) withObject:nil   waitUntilDone:YES];
                                                                        });

Then I load it into a tableView with no problems:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath: (NSIndexPath *)indexPath{
static NSString *CellIdentifier = @"PopulationCell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil){
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
Chatter *chatter = [_localChatters objectAtIndex:indexPath.row];

NSData *fbImageData = [NSData dataWithContentsOfURL:[NSURL URLWithString: chatter.url]];
UIImage *profilePicture = [UIImage imageWithData:fbImageData];
cell.imageView.image =profilePicture;

[cell.textLabel setAdjustsFontSizeToFitWidth: NO];

cell.textLabel.text = [NSString stringWithFormat:@"%@ joined at %@",chatter.name,chatter.joined];

cell.textLabel.textColor = [UIColor grayColor];

return cell;
}

However this includes the user information as well, which is something we don't want. In order to get around this problem I have created a separate method that would in theory create a second mutable array with just the data excluding the user's:

- (void)getData{
NSLog(@"%@",_localChatters);

NSMutableArray *newArray = [[NSMutableArray alloc] init];

for (NSInteger i = 0; i<[_localChatters count]; i++) {

    Chatter *newChatter = [_localChatters objectAtIndex:i];

    if ([newChatter.facebookID isEqualToString:_loggedInFBID]) {
    } else {

        [newArray addObject:newChatter];
    };
}
NSLog(@"%@",newArray);

}

However when this method is called from the view did load with a

 [self getData]

the _localChatters NSLogs as (null) and I believe subsequently the newArray is never filled and NSLogs as empty (). It is strange because when I log the _localChatters in the uitableview it is not null and of course all of the data is there when it loads. I'm at a loss why the _localChatters would read as null in this method when I am fairly certain the array loads just fine from the dispatch_async request.

EDIT:

Here is a small sample of JSON, I've removed some of the personal information such as FB ID and picture URL, however all of the objects are the same.

           "name": "Johnny",
           "room": "London",
           "latitude": 41.414483,
           "longitude": 2.152579,
           "message": "I agree, I think I'm going there right now",
           "timestamp": "9:23 PM",
           "url": " <<actual FB profile URL>>",
           "facebookID":"<<personal FB ID >>",
           "joined":"12:13 AM",

Don't name methods with the prefix "get" unless they return values by reference. — zaph
– zaph, Commented Jul 17, 2014 at 15:53
thanks @Zaph, I just slapped it together for a test, it wasn't meant to be a permanent solution. — canaanmckenzie
– canaanmckenzie, Commented Jul 17, 2014 at 15:56

blazejmar · Accepted Answer · 2014-07-17 15:53:37Z

2

The problem is multithreading. _localChatters array is created asynchronously so in most cases this will happen after viewDidLoad. You could move [self getData] to dispatch_async block (before reloading table view and after fetching data from JSON).

answered Jul 17, 2014 at 15:53

blazejmar

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