Tableviewcell controller uiviewimage slow

I have a uitableview cell that has an image like twitter app that I pull from the web via nsurl. I have it loading them in via the cells controller and of course when the user scrolls the app cOme to a crawl. How can only grab the images if/when scrolling stops if that is the best approach.

The other issue is I have that I call data refresh on the cell on viewdidload but that causes lag when the user comes out of the detail view back to the table. What method should I put my refresh call in. As I only need refresh开发者_StackOverflow中文版 if user pushes a refresh button or on initial tableview load.

Have a look at the http://developer.apple.com/library/ios/#samplecode/LazyTableImages/Introduction/Intro.html

The idea is to download images row per row and then display them when loaded in their rows without calling refresh ([tableView reloadData]) all the time - which causes "crawling".