表格视图中可见单元格的方法

Question

I want to download an image to my tableViewCell but I only want the image downloaded to be inside a cell who is VISIBLE in my tableview. I want my tableView to download image when the tableviewcell is visible and during that time to display a loading bar or something until the download is finished and then display that image to the corresponding tableviewcell

This is the code I use to display image to tableviewcell:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("ContentCell", forIndexPath: indexPath)

    let contentCell = cell as! ContentCell

    contentCell.thumbnail.kf_setImageWithURL(self.contentArray[indexPath.row].thumbnailUrl)
    print("row: \(indexPath.row)")


    return contentCell
}

What I get is all the image is download all at once. I know this because When I scroll down I find that all the image is instantly displayed without delay even though my logging method print() only print visible cell's row.

Am I implementing this wrong?

Answer 1

you will achieve using asynchronous image loading

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell" forIndexPath:indexPath];

cell.poster.image = nil; // or cell.poster.image = [UIImage imageNamed:@"placeholder.png"];

NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://myurl.com/%@.jpg", self.myJson[indexPath.row][@"movieId"]]];

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.poster.image = image;
            });
        }
    }
}];
[task resume];

return cell;

}