Interview guides / ios

Crashy notes list: iOS Interview Question

Crashy notes list interview question with a clear example answer for iOS engineers. Practice with AceMobileInterview.

This is a common iOS interview topic: Crashy notes list.

Below is a concise answer you can adapt in a real interview, then go deeper in the full AceMobileInterview track.

1. 1.Download the buggy zip. Deleting notes or opening detail can crash. Find unsafe indexing/force-unwraps and harden the flow (≈30–45 min).

   ## Scenario Notes list crashes on empty state and after rapid delete + detail tap. ## How to investigate - Turn on Exception Breakpoint - Reproduce: delete last note; delete then immediately tap a row - Search for `!` force unwraps and `notes[indexPath.row]` ## Planted bug 1: Force unwrap on selected note **Symptom:** Crash when opening detail with no selection **Root cause:** `detailNote!` in segue / push helper **Fix:** `guard let note else { return }`; disable detail when empty ## Planted bug 2: Stale index after delete **Symptom:** Out-of-bounds after delete animation **Root cause:** Action handler captures `indexPath.row` then mutates array before use **Fix:** Capture `note.id`; look up by id; or delete via `IndexPath` inside `performBatchUpdates` consistently ## Planted bug 3: Missing empty state **Symptom:** Table assumes ≥1 row elsewhere **Root cause:** `numberOfRows` can be 0 but toolbar still calls `notes[0]` **Fix:** Empty view; guard all `notes[i]` access ## Optimization tips - Prefer value ids over raw indexes across async UI callbacks - `fatalError` in production paths is a smell—use `assertionFailure` + recovery ## What to say in the interview - How you mapped crash stacks to the exact line - How you added a regression check (empty list + rapid tap)