Interview guides / android

Janky news list: Android Interview Question

Janky news list interview question with a clear example answer for Android engineers. Practice with AceMobileInterview.

This is a common Android interview topic: Janky news 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 Android zip. Opening the list with a large payload janks the UI. Find wrong-thread work and fix it (≈45–60 min).

   ## Scenario Compose/list screen freezes while parsing a large bundled JSON feed. ## How to investigate - Reproduce on launch with `assets/feed.json` - Android Studio CPU Profiler / Systrace - Search for `readText` / `Json.decodeFromString` on the main path ## Planted bug 1: Parse on Main **Symptom:** Frame freeze on first frame **Root cause:** Repository reads assets and decodes on `Dispatchers.Main` (or callers use `runBlocking` on main) **Fix:** `withContext(Dispatchers.Default)` for parse; `Dispatchers.IO` for asset read ## Planted bug 2: Bitmap work on UI thread **Symptom:** Scroll jank **Root cause:** `BitmapFactory.decodeByteArray` inside item composable / bind **Fix:** Decode on background; cache; use a proper image loader as stretch ## Planted bug 3: Architecture smell **Symptom:** Hard to test **Root cause:** Activity/ViewModel reaches into assets directly **Fix:** `FeedRepository` interface; inject fake in tests ## Optimization tips - Never `runBlocking` from a Composable - Prefer `StateFlow` updates after background work completes ## What to say in the interview - How you proved main-thread work before refactoring - What metric you re-checked after (time-to-content, jank frames)