iphone - How do I save memory when loading images from a URL in a Collection View? -

i have collection view in app , want load images url. collection view scrollable. if user scrolls down more images should paginated url.

what should images have loaded far? 1 way set pointer nil in order free space in heap. have load again, when user scrolls up.

is there better way handle scrolling , keep heap memory low possible?

use library sdwebimage or hjcache offers asynchronous download , memory , file caching features.