table view scrolling smooth with url images - ios

Question

I have a table view that loads title and images from url address. Since I added the images, the scrolling isn't smooth. I have changed the background to clear. The images are low resolution. I prefer accessing them with url, not to downloaded the image and re-upload it on the app. Looking forward for your solutions to make the scrolling smooth. Thanks
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
TableCell *cell = [tableView dequeueReusableCellWithIdentifier:#"TableCell" forIndexPath:indexPath];
NSString *str = [[feeds objectAtIndex:indexPath.row] objectForKey: #"title"];
[[cell textLabel] setNumberOfLines:0]; // unlimited number of lines
[[cell textLabel] setFont:[UIFont systemFontOfSize: 16.0]];
cell.backgroundColor = [UIColor clearColor];
cell.contentView.backgroundColor = [UIColor clearColor];
cell.TitleLabel.text=str;
UIImage *pImage=[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:feeds2[indexPath.row]]]];;
[cell.ThumbImage setImage:pImage];
return cell;
}

Answer 1

replace your code in cellForRowAtIndexPath:
after this line cell.TitleLabel.text=str;
That way you load each image in the background and as soon as its loaded the corresponding cell is updated on the mainThread.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void) {
NSData *imgData = NSData *imgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:feeds2[indexPath.row]]];
if (imgData) {
UIImage *image = [UIImage imageWithData:imgData];
dispatch_sync(dispatch_get_main_queue(), ^(void) {
UIImage *image = [UIImage imageWithData:imgData];
if (image) {
cell.ThumbImage.image = image;
}
});
});
A better approach is to cache the image , so you dont need to download them each time , the table scroll.
here are some very good references to accomplish this.
LazyTableImages Reference
SDWebImage
UIImageView+AFNetworking

Answer 2

Answer is simply you have to implement the loading with NSOperation where a custom class to handle your download and have your NSOperationQueue as downloadQueue. Every UITableView is a (sub class) UIScrollView therefore you can use the methods directly.
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
[downloadQueue cancelAllOperations]; // clear your queue
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
if (!decelerate) {
// start download only for visible cells
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
// start download only for visible cells
}
for more detail information visit this tutorial. There you can really find good solution for your need.