Android Compose & Kotlin Performance

Workflow

1. Identify the problem area:

   • Compose UI jank / recomposition → See references/compose.md
   • Coroutine communication / threading → See references/coroutines.md

2. Apply targeted fixes using the patterns in the relevant reference file.

3. Verify in release mode — debug builds disable Compose compiler optimizations and skippability, making profiling unreliable.

Quick Reference: Most Common Mistakes

Compose

• Reading state in parent when only child needs it — pass () -> T lambdas instead
• Using List/Map/Set params (unstable) — use kotlinx.collections.immutable or @Immutable
• Missing key in LazyColumn/LazyRow items
• Using Modifier.offset(x, y) instead of Modifier.offset { IntOffset(x, y) } for animated values
• Sorting/filtering inside composables instead of ViewModel
• Profiling in debug builds

Coroutines

• Using GlobalScope instead of viewModelScope/lifecycleScope
• Using synchronized/ReentrantLock instead of Mutex.withLock in coroutine code
• Collecting StateFlow without repeatOnLifecycle or collectAsStateWithLifecycle()
• Using Channel when SharedFlow is appropriate (one-to-many) or vice versa
• Running IO work on Dispatchers.Default or Dispatchers.Main

Recommended Architecture

• ViewModel: MutableStateFlow for UI state, exposed as StateFlow. Logic in viewModelScope.
• Repository/data layer: withContext(Dispatchers.IO) for disk/network. Expose Flow.
• Compose UI: Collect via collectAsStateWithLifecycle(). Defer reads via lambdas. Use stable types. Provide keys to lazy layouts.
• Cross-coroutine: Channel for one-to-one delivery, SharedFlow for one-to-many broadcast.
• Synchronization: Mutex.withLock over synchronized in coroutine code.