UIImageView+AFNetworking - need to scroll UICollectionView to set image - ios

Question

I'm using a UICollectionView and want to display images fetched from a server in it's cells. To do this I'm using UIImageView+AFNetworking. In my cellForItemAtIndexPath method I have the following code:
__weak CustomCollectionViewCell *weakCell = cell;
[cell.cellImageView setImageWithURLRequest:request
placeholderImage:placeholderImage
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
weakCell.cellImageView.image = image;
[weakCell setNeedsLayout];
} failure:nil];
The placeholder always show, but sometimes the downloaded images aren't showing. Any ideas on how I could solve this?

Answer 1

I suspect the problem is that you're on a background thread when you try to set the image, whereas you should always perform UI operations on the main thread.
Try setting the image in the main thread with something like
__weak CustomCollectionViewCell *weakCell = cell;
[cell.cellImageView setImageWithURLRequest:request
placeholderImage:placeholderImage
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
dispatch_async(dispatch_get_main_queue(), ^{
weakCell.cellImageView.image = image;
});
} failure:nil];

Answer 2

I'm pretty sure that AFNetworking moves all the block execution on the main thread, I'm just wondering if you are sure that those images are correctly downloaded.
Try to log the image size of the retuned image, and if it is present always use a failure block, maybe just printing the error.
Something like that:
typeof(self) __weak weakCell = cell; //but you don't need in that scenario
[cell.cellImageView setImageWithURLRequest:request
placeholderImage:placeholderImage
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
NSLog(#"Image %# scale %f", NSStringFromCGSize(image.size), image.scale);
weakCell.cellImageView.image = image;
[weakCell setNeedsLayout];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
NSLog(#"Error %#",error.localizedDescription);
}];

Answer 3

Solution for you question
SDWebImage
You just need to #import <SDWebImage/UIImageView+WebCache.h> to your project, and you can define also the placeholder when image is being downloaded with just this code:
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
MyCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"MyCell"
forIndexPath:indexPath];
DLog(#"url at index %d : %#", indexPath.row, ((MyObject *)[self.list.array objectAtIndex:indexPath.row]).imageUrl);
MyObject *object = (MyObject *)[self.list.array objectAtIndex:indexPath.row];
[cell.imageView setImageWithURL:[NSURL URLWithString:#"http://www.domain.com/path/to/image.jpg"]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
return cell;
}
It also cache downloaded images and gives you great performance.
Hope it will help you!

Answer 4

After downloading the images, I replaced
[self.myCollectionView reloadData]
with
[self.myCollectionView reloadSections:[NSIndexSet indexSetWithIndex:0]];
then refresh and it works well, you can try it.