UITableView lazy-loaded image does not load until finger is off - ios

Question

I have an app where I load a lot of large images. When I lazy-load them, and even after the image has been loaded, the cell does not load them until I take my finger off the screen. I am calling my downloadImageForVisiblePaths function in the UIScrollViewDelegate methods scrollViewDidEndDragging and in scrollViewDidEndDecelerating apart from this, I am also setting the image in the UITableView's cellForRowAtIndexPath method like so:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
// Code to load reusable custom cell
CustomObject *object = (CustomObject*) [self.tableArray objectAtIndex: indexPath];
if(!object.mainImage){
[self downloadImageForIndexPath:indexPath];
cell.mainImageView.image = [UIImage imageNamed:#"placeholder"];
}else{
cell.mainImageView.image = object.mainImage;
}
return cell;
}
Where the downloadImageForIndexPath looks like this:
-(void) downloadImageForIndexPath:(NSIndexPath*) indexPath{
UIImage *loadedImage = [[UIImage alloc] init];
// take url and download image with dispatch_async
// Once the load is done, the following is done
CustomCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
cell.mainImageView.image = loadedImage;
CustomObject *object = (CustomObject*) [self.tableArray objectAtIndex: indexPath];
object.mainImage = loadedImage;
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableVIew reloadData];
});
}
I can't see where I am going wrong. I need the images to load even when the finger is on the screen. This behaviour is similar to how the images load on apps like Google+, Instagram or Facebook.
Any pointers will be much appreciated.

Answer 1

It's hard to tell since you didn't include all the code for downloadImageForIndexPath, but it looks like you are assigning an image to a cell from a background thread (you shouldn't touch UI controls from background threads). Also, if you'r updating cell directly, you don't need to call reloadData.
I would also suggest using SDWebImage for displaying remote images in a tableview.