👀 Views: 55 💬 Answers: 1 📅 Created: 2025-08-08

objective-c uicollectionview urlsession image-loading performance Objective-C

I'm having a hard time understanding I'm confused about I'm facing a challenge with asynchronously loading images in a `UICollectionView` using Objective-C... Despite using `NSURLSession` to fetch images, I'm noticing that the images do not appear in the cells until the scrolling has stopped, leading to a poor user experience. I configured my `UICollectionViewCell` like this: ```objective-c - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"CellIdentifier" forIndexPath:indexPath]; NSString *imageURLString = self.imageURLs[indexPath.row]; // Reset cell's image cell.imageView.image = nil; NSURL *imageURL = [NSURL URLWithString:imageURLString]; NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:imageURL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (error) { NSLog(@"Error fetching image: %@", error); return; } UIImage *image = [UIImage imageWithData:data]; if (image) { dispatch_async(dispatch_get_main_queue(), ^{ cell.imageView.image = image; }); } }]; [task resume]; return cell; } ``` This approach seems to create a lag as the cells load images only once I stop scrolling. I verified that the data is being fetched correctly, and the `completionHandler` is being called as expected. However, it seems like the UI updates aren't happening until after the scrolling stops. I even tried prefetching images using the `UICollectionViewDataSourcePrefetching` protocol, but it still didn't address the issue effectively. Here is how I attempted to implement prefetching: ```objective-c - (void)collectionView:(UICollectionView *)collectionView prefetchItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths { for (NSIndexPath *indexPath in indexPaths) { NSString *imageURLString = self.imageURLs[indexPath.row]; NSURL *imageURL = [NSURL URLWithString:imageURLString]; // Start fetching images asynchronously NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:imageURL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { // Handle data as before }]; [task resume]; } } ``` Despite these attempts, the images still don't load smoothly during the scroll. I've tried using `setNeedsLayout` and `layoutIfNeeded` in hopes of forcing the layout to update, but that didn't help either. I’d appreciate any advice on how to improve the performance of image loading in this context or any best practices to follow when working with `UICollectionView` in this manner. Am I missing something crucial in my implementation? I'm working on a API that needs to handle this. I'd really appreciate any guidance on this. I'd love to hear your thoughts on this. I'm working on a application that needs to handle this.