tabelviewcell中的异步图像下载？

Question

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     static NSString *CellIdentifier = @"cell";
     TVcell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
     if (cell == nil) {
         cell = [[TVcell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
     }
     cell.titleLabel.text = [[[arrayData objectAtIndex:indexPath.row]valueForKey:@"title"]stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

     cell.txtlabel.text = [[[arrayData objectAtIndex:indexPath.row] valueForKey:@"description"]stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
     cell.tag = indexPath.row;
     cell.imageView.image = nil;
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
     dispatch_async(queue, ^(void) {

     NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[enclosureUrlArray objectAtIndex:indexPath.row]]];

     UIImage* image = [[UIImage alloc] initWithData:imageData];
     if (image) {
         dispatch_async(dispatch_get_main_queue(), ^{
             if (cell.tag == indexPath.row) {
                 cell.IMGLabel.image = image;
                 [cell setNeedsLayout];
                 }
              });
          }
      });
      return cell;

}

while i'm scrolling that same images are appearing on the cells,which cells im reusing.i used scroll view delegate also.im storing urls in enclosureUrlArray and i'm passing.

Answer 1

Put cell.IMGLabel.image = nil in your cellForRowAtIndexPath before downloading image, ie below cell.imageView.image = nil; this line.

Or set some place holder image (no image available kind of image to cell's image in interface builder), so if image is not downloaded then it will show this place holder image otherwise it will show downloaded image.

SDWebImage is good for this kind of case. It will cache the images so it will give better performance also. There is nothing wrong to use any good third party library.

Answer 2

By using SDWeb image:

#import <SDWebImage/UIImageView+WebCache.h>

...

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *MyIdentifier = @"MyIdentifier";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
                                       reuseIdentifier:MyIdentifier] autorelease];
    }

    // Here we use the new provided sd_setImageWithURL: method to load the web image
    [cell.imageView sd_setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                      placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

    cell.textLabel.text = @"My Text";
    return cell;
}

Answer 3

You can also use NSURLSession as well,see this link

Async image loading from url inside a UITableView cell - image changes to wrong image while scrolling

 NSURL *url = [NSURL URLWithString:[enclosureUrlArray objectAtIndex:indexPath.row]];
 NSURLSessionTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    if (data) {
        UIImage *image = [UIImage imageWithData:data];
        if (image) {
            dispatch_async(dispatch_get_main_queue(), ^{
                MyCell *updateCell = (id)[tableView cellForRowAtIndexPath:indexPath];
                if (updateCell)
                    updateCell.IMGLabel.image = image;
            });
        }
    }
}];
[task resume];

works perfect for me..

Answer 4

with the help of sdwebimage you can show the image like this:-

NSString *string2 = [[businessListArray objectAtIndex:indexPath.row ]valueForKey:@"logo"];
    NSURL *url1 = [NSURL URLWithString:
                   [NSString stringWithFormat:
                    @"%@%@",
                    @"http://dev-demo.info.bh-in-15./upload/post/",
                    string2]];

    UIImageView *imageView = (UIImageView *)[cell.contentView viewWithTag:301];

    [imageView sd_setImageWithURL:url1
                 placeholderImage:[UIImage imageNamed:@"pocket.png"]
                        completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                            imageView.image = image;
                        }];