Question

I would like to create an iphone application that displays three rows of infinite number of images that should be coming from AWS S3 and loaded on the fly while the user is scrolling to the right on each row.
What I would like to do is have the top row small, middle row large and bottom row small. Caching and smart lazy loading for memory managment is critical.

I looked at Three20 but too complicated for such a simple task. Any idea of simple libraries or even better a native approach.

Answer 1

You should take a closer look at UIScrollView. Apple has created this class for the specific intentions of scrolling content. There are quite a few samples available from Apple, and they discussed this specific issue of content re-use and high quality scrolling at the most recent WWDC.

This basic strategy is to display content, and loop the scroll position in the same frame that the update thread would animate. This results in moving the content at the perfect moment to fool the user in to believing the content is ‘infinite’.

Review:
WWDC 2010: Session 104 – Designing Apps with Scroll Views

WWDC 2011 : Session 104 – Advanced Scroll View Techniques; Session 115 – Scrolling, Swiping, Dragging

While the concept is pretty easy to grasp, seeing how Apple accomplishes this task, and incorporating their best practices will result in the best code you can write for this platform.