table view scrolling smooth with url images

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;

}

load image on background thread , not on main thread.

Pawan Rai
– Pawan Rai

2014-06-08 19:33:04 +00:00
Commented Jun 8, 2014 at 19:33 — Pawan Rai
– Pawan Rai, Commented Jun 8, 2014 at 19:33

Community · Accepted Answer · 2017-05-23 12:33:02Z

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

Goppinath · Accepted Answer · 2014-06-08 19:44:34Z

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.

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