Does NSURLConnection Block the Main/UI Thread

Question

I am downloading images in table view cells as they scroll onto the screen. For UX reasons, I start downloading the images in - (UITableViewCell *)tableView:(UITableVi

Answer 1

I have experienced this problem before. The asynchronous delegate methods of NSURLConnection are not firing while a scrollView is being scrolled. Although the downloading works in the background, your main thread is not informed of new images. Just like you, I believe the problem is related to scrollviews being scrolled in an inner NSRunLoop with a different RunLoopMode. I have been talking to Apple staff about this and have them look at my code, but we couldn't work out a solution.

On the other hand Jeff LaMarche has this post on his blog, where he does the same thing, and it works as expected. I have not been able to figure out what he does differently (mainly due to not having time), but this may be worth a look.