Interview guides / android

God MainActivity: Android Interview Question

God MainActivity interview question with a clear example answer for Android engineers. Practice with AceMobileInterview.

This is a common Android interview topic: God MainActivity.

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

1. 1.MainActivity mixes networking, parsing, prefs, and UI with a hardcoded API key. Refactor the worst smells (≈45–60 min).

   ## Scenario God Activity with a committed secret. ## How to investigate - Skim `MainActivity.kt` responsibilities - Grep for API keys - Find main-thread `FileOutputStream` / prefs heavy writes ## Planted bug 1: Hardcoded API key **Symptom:** Secret in repo **Root cause:** `const val API_KEY = "sk_live_..."` **Fix:** BuildConfig / local properties placeholder; stub in exercise ## Planted bug 2: God object **Symptom:** Untestable **Root cause:** OkHttp + JSON + SharedPreferences + UI in Activity **Fix:** Extract `SettingsRepository` + ViewModel; Activity/Compose only collects state ## Planted bug 3: Main-thread disk write **Symptom:** Hitch on Save **Root cause:** Synchronous write on click handler **Fix:** `Dispatchers.IO`; then toast on Main ## Optimization tips - Interview success = clear boundaries, not perfect DI graph - Mention how you’d unit test the repository ## What to say in the interview - Secret removal first - What you deferred on purpose