When is it worthwhile to cache UIImage resources?

Question

I\'ve been doing a lot of iPhone UI work with image files that are used in multiple locations in a single view or in several views throughout the application. In some cases,

Answer 1

In the latest performance sessions at WWDC (2011), Apple didn't recommend caching images for most cases. They recommend that you only cache images when you know for a fact, after a performance analysis, that you need to cache images ahead of time because you can't afford the time to load them off disk and decode them. In most cases you probably can afford it.

They specifically noted, as @Till does, that +[UIImage imageNamed:] caches images for the lifetime of your process, and so they recommend using a non-caching loading method, such as +[UIImage imageWithContentsOfFile:]

The reason is that memory is a constrained resource on iOS devices, so if you cache your images, you are likely to cause memory pressure on the system, and apps to get jetsammed. And since iOS 5 jetsams apps using more memory first, if you're caching a bunch of UIImages you're going to make it more likely for your app to get jetsammed.