iOS Developer interview question
How do you manage memory in an iOS app?
iOS memory management combines ARC ownership with bounded caches and release of large resources; inspect the memory graph and Instruments for cycles, unbounded growth, and allocations that survive their owner.
Direct answer
What a strong answer covers
How it works
Most iOS memory work is ownership hygiene: knowing which object owns which, breaking cycles with weak references, and releasing large resources such as decoded images, video buffers, and Core Data contexts when their screen goes away. Caches use NSCache or an explicit size limit so they shrink under pressure, and the app responds to memory warnings by dropping regenerable data. The memory graph debugger shows who retains a suspicious object, Instruments’ Allocations and Leaks templates show growth over time, and the goal is a flat memory line after repeating the same navigation many times.
Example
Pushing and popping a photo editor twenty times raised memory by 40 MB each cycle; the memory graph showed the editor retained by a CADisplayLink that was never invalidated. Invalidating it in viewWillDisappear brought the line flat, and image thumbnails moved into an NSCache with a 50 MB cost limit so the grid stops growing without bound.
Common mistakes
- Storing full-resolution UIImages in an array as a cache.
- Ignoring memory warnings and getting terminated by jetsam on older devices.
- Chasing small allocations in Instruments while one retained view controller holds hundreds of megabytes.
A useful answer structure
Answer from your own work.
Do not memorise a script: use only examples you can explain honestly in follow-up questions.
Open the desktop workspace and rehearse a clear answer in your own words.