Is it possible to know if an image is in the iPhone system cache?

Question

I am trying to improve scrolling performance of a UITableView. I am loading the images using imageNamed: and dispatch_async, but scrolling is very good once the images have been loaded into the cells. I would like to fade in the images only if they are not in the system cache to reduce the jarring effect of the images "popping" into view.

Is there a way to know if an image is already in the system cache?

Thanks for the help!

Answer 1

There is no documented way to look inside the UIImage to check such things.

I think the only way to know for sure that the image is available immediately, is to force the UIImage to be loaded. This can be done in the background, by creating the UIImage and accessing it's pixels, using CGImage functions. If you ensure that there is no rescaling needed (i.e. don't put a 3000x2000 image in a 30x20 space) then it should display without a glitch.