Need advice on speeding up tableViewCell photo loading performance

Question

I have around 20 tableview cells that each contain a number (2-5) thumbnail sized pictures (they are VERY small Facebook profile pictures, ex. http://profile.ak.fbcdn.net/hprofile-ak-sf2p/hs254.snc3/23133_201668_2989_q.jpg). Each picture is an UIImageView added to the cell's contentview.

Scrolling performance is poor, and measuring the draw time I've found the UIImage rendering is the bottleneck.

I've researched/thought of some solutions but as I am new to iphone development I am not sure which strategy to pursue:

• preload all the images and retrieve them from disk instead of URL when drawing cells (I'm not sure if cell drawing will still be slow, so I want to hold off on the time investment here)
• Have the cells display a placeholder image from disk, while the picture is asynchronously loaded (this seems to be the best solution, but I'm currently not sure exactly how to do best do this)
• There's the fast drawing recommendation from Tweetie, but I don't know that will have much affect if it turns out my overhead is in network loading (http://blog.atebits.com/2008/12/fast-scrolling-in-tweetie-with-uitableview/)

Thoughts/implementation advice? Thanks!

Answer 1

Suggest you do a search in the XCode help docs for LazyTableImages. It's a sample app provided by Apple that asynchronously loads images into a table cell. It should be a good starting point.

You'll probably want to add a local cache to save the images so you don't have to keep downloading them each time, and a way to prune out old images out of the cache.