Lazy loading images in a UITableView that has a scroll index

I think this is a new spin on an old question, but I'm completely stuck here.

In my app, I have a UITableView with 650 cells, each with a custom 16x16 RGB icon. On most recent iOS devices, loading all of those icons into memory before displaying the table works totally fine, but on older hardware, I'd like to implement a lazy load system that only loads icons it needs.

I've implemented the Apple LazyTableImages example, (which uses a UIScrollView delegate to determine when the table stops moving to load the visible icons), but I've run into another snag.

My UITableView also has a section index display (ie the list of labels on the right hand side you can swipe up and down to scroll quickly), and the LazyTableImages example hasn't taken this into account. If I scroll using the index, the images won't lazy-load. :(

As far as I can see, the scroll index doesn't actually have any delegate events it triggers. So I'm wondering, has anyone else tried to implement lazy-loading on a table with a scroll index? Is ther开发者_开发百科e any way to track the index and find out if the user has interacted with it?

Thanks!

After buzzing around a few of my iOS developer buddies, I came up with a solution that worked well enough.

I set it up so that in addition to the icons being loaded from the UIScrollView delegates, an NSTimer object will periodically call a method that checks the currently visible table cells ([UITableView indexPathsForVisibleRows]) every .5 seconds, and loads any icons on the screen that haven't been loaded yet in a single separate thread.

I tried to make the solution as efficient as possible, so I made sure the timer was only active when the tableView was visible and stationary, and I liked it since it meant that every visible icon regardless was addressed.

One thing I discovered was that if the tableView was reloaded while the thread was looping through the visible cells (rare, but was possible), it would crash. The solution to this was to make sure each cell data source entry was retained while the icon was being loaded.