ios - UICollectionView doesn't update immediately when calling reloadData, but randomly after 30-60 seconds

Question

As the title implies, my UICollectionView doesn't update and display the cells immediately after calling reloadData. Instead, it seems to eventually update my collection view after 30-60 seconds. My setup is as follows:

UICollectionView added to view controller in Storyboard with both delegate and dataSource setup for the view controller and standard outlet setup numberOfSectionsInRow & cellForItemAtIndexPath are both implemented and reference the prototyped cell and the imageView inside of it

Here is the code that goes to Twitter, get's a timeline, assigns it to a variable, reloads a table view with the tweets and then goes through the tweets to find photos and reloads the collection view with those items.

Even if I comment out the code to display the image, it still doesn't change anything.

SLRequest *timelineRequest = [SLRequest requestForServiceType:SLServiceTypeTwitter requestMethod:SLRequestMethodGET URL:timelineURL parameters:timelineParams];
[timelineRequest performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error) {
    if(responseData) {
        JSONDecoder *decoder = [[JSONDecoder alloc] init];

        NSArray *timeline = [decoder objectWithData:responseData];

        [self setTwitterTableData:timeline];

        for(NSDictionary *tweet in [self twitterTableData]) {
            if(![tweet valueForKeyPath:@"entities.media"]) { continue; }

            for(NSDictionary *photo in [[tweet objectForKey:@"entities"] objectForKey:@"media"]) {
                [[self photoStreamArray] addObject:[NSDictionary dictionaryWithObjectsAndKeys:
                                                    [photo objectForKey:@"media_url"], @"url",
                                                    [NSValue valueWithCGSize:CGSizeMake([[photo valueForKeyPath:@"sizes.large.w"] floatValue], [[photo valueForKeyPath:@"sizes.large.h"] floatValue])], @"size"
                                                    , nil]];
            }
        }

        [[self photoStreamCollectionView] reloadData];
    }
}];

Answer 1

This is a classic symptom of calling UIKit methods from a background thread. If you view the -[SLRequest performRequestWithHandler:] documentation, it says the handler makes no guarantee of which thread it will be run on.

Wrap your call to reloadData in a block and pass this to dispatch_async(); also pass dispatch_get_main_queue() as the queue argument.