Lazy loading in uicollectionview

Question

here is the code for my collectionview it is showing records but loading really please tell me how can i implement lazy loading on this i also have a placeholder pic in my project

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

// Setup image name
    NSString *url = [[rssOutputData objectAtIndex:indexPath.row]xmllink];
    UIImage *img = nil;
    NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
    img = [[UIImage alloc] initWithData:data];

    cell.MJImageView.image = img;
    return cell;
}

right now it is working but very very slow.

Answer 1

It's pretty easy to do lazy loading using GCD.

    // Create a queue for the operations
    dispatch_queue_t queue = dispatch_queue_create("photoList", NULL);

    // Start getting the data in the background
    dispatch_async(queue, ^{
        NSData* photoData = [NSData dataWithContentsOfURL:[NSURL URLWithString:object.photoURL]];
        UIImage* image = [UIImage imageWithData:photoData];

        // Once we get the data, update the UI on the main thread
        dispatch_sync(dispatch_get_main_queue(), ^{
           cell.photoImageView.image = image;
        });
    });

Answer 2

The easiest way to implement that is use SDWebImage library, it does right what you need. There is UIImageView category that will allow you to modify code for that:

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

    // Setup image name
    NSString *url = [[rssOutputData objectAtIndex:indexPath.row]xmllink];
    [cell.MJImageView sd_setImageWithURL:[NSURL URLWithString:url]];
    return cell;
}