Lazy loading in uicollectionview - ios

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;
}

Answer 3

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString: #"url.com"]];
UIActivityIndicatorView * indicator = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
[yourImageView addSubview:indicator];
indicator.center = yourImageView.center;
[indicator startAnimating];
[yourImageView setImageWithURLRequest:request
placeholderImage:[UIImage imageNamed:#"placeholder.png"]
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
dispatch_async(dispatch_get_main_queue(), ^(void){
yourImageView.image = image;
});
[indicator stopAnimating];
[indicator removeFromSuperview];
} failure:nil];

Answer 4

Maybe, because your image is so large
You can use NSThread for loading
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
CollectionViewCell* cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"MJCell" forIndexPath:indexPath];
cell.tag = indexPath.row; //For index
[NSThread detachNewThreadSelector:#selector(loadImage:) toTarget:self withObject:cell];
return cell;
}
- (void) loadImage:(CollectionViewCell *)cell {
NSString *url = [[rssOutputData objectAtIndex:cell.tag]xmllink];
UIImage *img = nil;
NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
img = [[UIImage alloc] initWithData:data];
cell.MJImageView.image = img;
}