I am trying to display some images from URL into my collection view. But when i try to do so, my images get displayed on collection view but they randomly keep refreshing and reloaded. Also when i try to scroll the collectionView, it again reloads the whole data, which i don't want. I just want to display images like a preview to user. 
Here below is my code to fetch the images from URL and display it on collection View.

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

 __block  NSString *filename;     

for(NSDictionary *item in [jsonSD objectForKey:@"Data"]) {       
      for (int i=0; i<=[[item objectForKey:@"Count"]integerValue]; i++) {
         filename=[NSString stringWithFormat:@"http://..URL../media/content/%@%@%d_1.png",_getstring,[item objectForKey:@"subcategory_id"],i];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{     
              NSURL *url = [NSURL URLWithString:filename];
                  [self downloadImageWithURL:url completionBlock:^(BOOL succeeded, NSData *data) {
                                if (succeeded) {
                                    iv.image = [[UIImage alloc] initWithData:data];                                        
                                }
                                    }];

                      });
    }
  }

return cell;
}

- (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, NSData *data))completionBlock
{
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
    if (!error) {
        completionBlock(YES, data);
    } else {
        completionBlock(NO, nil);
    }
}];
}

```

Here 'iv' is my imageView, where i display the images on cell of collection view. 
I tried searching related contents but i didn't got any idea for above problem.

Please help me. Any help is appreciated.