Implementation.m

- (void)setImageWithURL:(NSURL *)url;
 
- (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage;

UICollectionViewCell.m

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    
    //here is where you set the image using the one line of code
    [cell.imageView setImageWithURL: [NSURL URLWithString:@"https://url/to/image.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder"]];
    return cell;
}

UITableViewCell.m

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"Cell";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }
    
   //here is where you set the image using the one line of code
    [cell.imageView setImageWithURL: [NSURL URLWithString:@"https://url/to/image.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder"]];
    return cell;
}