DDURLConnection.h

#import <Foundation/Foundation.h>

typedef void (^DDURLCompletionBlock)(NSData *responseData, NSError *error);

@interface DDURLConnection : NSURLConnection
- (id)initWithRequest:(NSURLRequest *)request startImmediately:(BOOL)startImmediately completion:(DDURLCompletionBlock)completionBlock;
@end

DDURLConnection.m

#import "DDURLConnection.h"

@interface DDURLConnection () <NSURLConnectionDataDelegate>
@property (strong, nonatomic) DDURLCompletionBlock completionBlock;
@end

@implementation DDURLConnection

- (void)dealloc
{
    self.completionBlock = nil;
}

- (id)initWithRequest:(NSURLRequest *)request startImmediately:(BOOL)startImmediately completion:(DDURLCompletionBlock)completionBlock;
{
    self = [super initWithRequest:request delegate:self startImmediately:startImmediately];
    if (self)
    {
        if (completionBlock)
            self.completionBlock = completionBlock;
            
    }
    
    return self;
}

#pragma mark - NSURLConnectionDataDelegate

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"connection: %@ didFailWithError: %@", connection, error);
    if (self.completionBlock) self.completionBlock(nil, error);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    if (self.completionBlock) self.completionBlock(data, nil);
}

@end

DDViewController.m

#import "DDViewController.h"
#import <AVFoundation/AVFoundation.h>
#import "DDURLConnection.h"

@interface DDViewController () <UITableViewDataSource, UITableViewDelegate, NSURLConnectionDelegate>
@property (strong, nonatomic) UITableView *tableView;
@property (strong, nonatomic) NSArray *photo_urls;
@end

@implementation DDViewController
@synthesize photo_urls;

- (void)dealloc
{
    photo_urls = nil;
}

- (id)init
{
    self = [super init];
    if (self)
    {
        self.tableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStylePlain];
        self.tableView.dataSource = self;
        self.tableView.delegate = self;
        [self.view addSubview:self.tableView];
        
        NSMutableArray *urls = [NSMutableArray arrayWithCapacity:20];
        for (int i = 0; i < 25; i++)
        {
            [urls addObject:@"https://d2pnn7clgn6qxc.cloudfront.net/assets/products/mens/jeans/swatch/raw-premium/indigo-natural.jpg"];
        }
        photo_urls = urls;
    }
    
    return self;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    
    self.tableView.frame = self.view.bounds;
}

#pragma mark - Getters

- (NSInteger)imageViewTag
{
    return 1415;
}

#pragma mark - Table view data source

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return photo_urls.count;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    return 320;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MemeCell"];
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"MemeCell"];
    }
    
    // Dequeue subviews
    UIImageView *imageView = (UIImageView *)[cell viewWithTag:[self imageViewTag]];
    if (!imageView)
    {
        imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 320)];
        imageView.tag = [self imageViewTag];
        [cell addSubview:imageView];
    }
    
    NSInteger activityTag = 54321;
    if (!imageView.image && ![cell viewWithTag:activityTag])
    {
        UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
        activityIndicator.tag = activityTag;
        activityIndicator.center = cell.center;
        activityIndicator.hidesWhenStopped = YES;
        [activityIndicator startAnimating];
        [cell addSubview:activityIndicator];
        
        // No image set... fetch it on a background thread & set it dyanmically (weak reference).
        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[photo_urls objectAtIndex:indexPath.row]]];
        __block DDURLConnection *openConnection = [[DDURLConnection alloc] initWithRequest:request startImmediately:YES completion:^(NSData *responseData, NSError *error)
        {
            [activityIndicator stopAnimating];
            
            UIImage *image = [[UIImage alloc] initWithData:responseData];
            if (!error && image)
            {
                imageView.image = image;
                
                // Removing activityIndicator from it's superview will reset the cell's -viewWithTag: results.
                // The imageView's image is set so we don't need to make another DDURLConnection
                [activityIndicator removeFromSuperview];
            }
            
            openConnection = nil; // Dealloc
        }];
    }
    
    return cell;
}

@end