NSCache and background
ios, nscache
Solution
In my case, that happened when objects stored in NSCache does not conform to NSDiscardableContent protocol. When I added the said protocol, eviction of objects when the app is entering background disappears.
In addition, based on source of NSCache.m I found here, objects that do not conform to NSDiscardableContent protocol are never removed at runtime even the app needs more memory and should evict some of its elements. Maybe that's the reason why non-NSDiscardableContent objects are evicted when the app is entering background because that's a good time for them to be evicted.
Problem
I've noticed that NSCache evicts all of its object when the application goes in background. is that the expected behaviour? is there a way to avoid it? I would expect it to evict objects when the device run out of memory not immediately when the app goes in background. Do you know any valid alternative?