JSON中的数据未在UICollectionView中更新

Question

I'm creating an app with a Newsfeed as a UICollectionView however it doesn't seem to update when I change the JSON file. I am using a UIRefreshControl to refresh it but I can't tell if my issue is to do with this or to do with how the JSON is read (or something else entirely).

viewDidLoad

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];


    self.navigationItem.title = @"News";

    UIButton *btn =  [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(0,0,23,16);
    [btn setBackgroundImage:[UIImage imageNamed:@"menuImage.png"] forState:UIControlStateNormal];
    [btn addTarget:(NavigationViewController *)self.navigationController action:@selector(showMenu) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *barBtn = [[UIBarButtonItem alloc] initWithCustomView:btn];
    self.navigationItem.leftBarButtonItem = barBtn;

    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    _session = [NSURLSession sessionWithConfiguration:config
                                             delegate:self
                                        delegateQueue:nil];
    [self fetchFeed];



    UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];

    CGRect screenRect = [[UIScreen mainScreen] bounds];
    CGFloat frameWidth = screenRect.size.width - 20;
    CGFloat frameHeight = screenRect.size.height - 20;

    _collectionView=[[UICollectionView alloc] initWithFrame:CGRectMake(10, 10, frameWidth, frameHeight) collectionViewLayout:layout];
    [_collectionView setDataSource: self];
    [_collectionView setDelegate: self];

    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
    [_collectionView setBackgroundColor:[UIColor clearColor]];


    [self.view addSubview:_collectionView];



    UIRefreshControl * refreshControl = [[UIRefreshControl alloc] init];
    refreshControl.attributedTitle = [[NSAttributedString alloc] initWithString:@"Refresh Images"];
    [_collectionView addSubview:refreshControl];
    [refreshControl addTarget:self action:@selector(refresh:) forControlEvents:UIControlEventValueChanged];

    [self.collectionView reloadItemsAtIndexPaths:[self.collectionView indexPathsForVisibleItems]];
    [self.collectionView reloadData];

}

fetchFeed

- (void)fetchFeed
{
    NSString *requestString = @"http://www.jameslester.xyz/example.json";
    NSURL *url = [NSURL URLWithString:requestString];
    NSURLRequest *req = [NSURLRequest requestWithURL:url];

    NSURLSessionDataTask *dataTask = [self.session dataTaskWithRequest:req
                                    completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                        NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:data
                                                                                                   options:0
                                                                                                     error:nil];
                                        self.articles = jsonObject[@"articles"];

                                        NSLog(@"%@", self.articles);
                                        NSLog(@"Feed Fetched!!!");

                                        dispatch_async(dispatch_get_main_queue(), ^{[self.collectionView reloadData];
                                    });
                                    }];


    [dataTask resume];
}

refresh

- (void)refresh:(id)sender
{

    [self fetchFeed];

    [(UIRefreshControl *)sender endRefreshing];

    NSLog(@"Refreshed");
}

Any help will be really appreciated.

Collection View Data Source

#define LABEL_TAG 100001

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath];

    UILabel *articleTitle = [cell.contentView viewWithTag:LABEL_TAG];
    NSDictionary *article = self.articles[indexPath.row];

    if (!articleTitle) {
        articleTitle = [[UILabel alloc]initWithFrame:CGRectMake(5, cell.bounds.size.height - cell.bounds.size.height / 2.2, cell.bounds.size.width - 10, cell.bounds.size.height / 2)];
        articleTitle.textColor = [UIColor whiteColor];
        articleTitle.numberOfLines = 3;
        articleTitle.adjustsFontSizeToFitWidth = YES;
        articleTitle.tag = LABEL_TAG;
        [cell.contentView addSubview:articleTitle];
    }

    articleTitle.text = article[@"title"];

    NSData * imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: article[@"image"]]];

    UIImageView *bgImageView = [[UIImageView alloc] initWithImage:[UIImage imageWithData:imageData]];

    [bgImageView setContentMode:UIViewContentModeScaleAspectFill];
    [bgImageView setClipsToBounds:YES];

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = CGRectMake(0, cell.bounds.size.height - cell.bounds.size.height / 2, cell.bounds.size.width, cell.bounds.size.height/2);
    gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor clearColor] CGColor], (id)[[UIColor blackColor] CGColor], nil];
    //gradient.locations = [NSArray arrayWithObjects:[NSNumber numberWithInt:0.0],[NSNumber numberWithInt:0.5], nil];
    [bgImageView.layer insertSublayer:gradient atIndex:0];

    cell.backgroundView = bgImageView;

    return cell;
}


- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionView *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 10; // This is the minimum inter item spacing, can be more
}


- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 10;
}


- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGRect screenRect = [[UIScreen mainScreen] bounds];
    CGFloat screenWidth = screenRect.size.width;

    int x = screenWidth/2 - 15;
    int y = x;

    return CGSizeMake(x, y);
}


- (void)collectionView:(UICollectionView *)colView didSelectItemAtIndexPath:(nonnull NSIndexPath *)indexPath
{
    NSDictionary *article = self.articles[indexPath.row];
    NSURL *URL = [NSURL URLWithString:article[@"url"]];

    self.webViewController.title = article[@"title"];
    self.webViewController.URL = URL;
    [self.navigationController pushViewController:self.webViewController
                                         animated:YES];
}

Answer 1

Try to this

- (void)fetchFeed { 
    NSString *requestString = @"http://www.jameslester.xyz/example.json"; 
    NSURL *url = [NSURL URLWithString:requestString];
    NSURLRequest*req = [NSURLRequest requestWithURL:url]; 

    NSURLSessionDataTask*dataTask = [self.session dataTaskWithRequest:req completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { 
    NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil]; 
    self.articles = jsonObject[@"articles"]; 
    NSLog(@"%@", self.articles); 
    NSLog(@"Feed Fetched!!!"); 

        dispatch_async(dispatch_get_main_queue(), ^{
            [_collectionView reloadData]; 
        }); 
    }]; 
    [dataTask resume]; 
}

Answer 2

If NSLog(@"%@", self.articles) works and shows data you have proven that you are getting network data back. Did you set up your UIView as the delegate and the datasource properly? This is usually done at the top of the UIViewController class and looks like this:

class MyClassName: UICollectionViewDataSource {
   // Your code here.
}

One way to check if the datasource is set up correctly is to set a breakpoint here

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
   print(“This shows that I’m getting called”)
   // Your custom code
}

When you call

dispatch_async(dispatch_get_main_queue(), ^{
    [self.collectionView reloadData];
})

this will in turn call cellForItemAtIndexPath to display data. If cellForItemAtIndexPath isn't called then you have not properly set your UICollectionViewDataSource