compose-anti-patterns

Compose / Kotlin Android Anti-Patterns

Reject these in generated code. Each entry has a BAD example and the CORRECT replacement.

1. View-system leak: findViewById in a Compose project

// BAD
val btn = findViewById<Button>(R.id.submit)
btn.setOnClickListener { ... }

// CORRECT
Button(onClick = { ... }) { Text("Submit") }

Mixing XML layouts and Compose in the same screen forces both engines to run. New screens should be pure Compose.

2. setContentView(R.layout.x) instead of setContent { ... }

// BAD
class MainActivity : AppCompatActivity() {
    override fun onCreate(b: Bundle?) {
        super.onCreate(b)
        setContentView(R.layout.activity_main)
    }
}

// CORRECT
class MainActivity : ComponentActivity() {
    override fun onCreate(b: Bundle?) {
        super.onCreate(b)
        setContent { AppTheme { AppNavHost() } }
    }
}

3. GlobalScope.launch { }

// BAD - leaks, no lifecycle
GlobalScope.launch { repo.sync() }

// CORRECT - viewModelScope / lifecycleScope / rememberCoroutineScope
viewModelScope.launch { repo.sync() }

GlobalScope survives configuration changes, screen destruction, and process death. Anything started in it leaks until the process dies.

4. LiveData when StateFlow is the default

// BAD
val name: LiveData<String> = MutableLiveData("")
val displayName by vm.name.observeAsState("")

// CORRECT
private val _name = MutableStateFlow("")
val name: StateFlow<String> = _name.asStateFlow()

// in composable
val displayName by vm.name.collectAsStateWithLifecycle()

LiveData works but is legacy. New code uses StateFlow for state, SharedFlow for events.

5. Public MutableStateFlow / MutableState

// BAD
val count = MutableStateFlow(0)   // anyone can mutate

// CORRECT
private val _count = MutableStateFlow(0)
val count: StateFlow<Int> = _count.asStateFlow()

Same rule as Java: expose the read-only contract, keep the mutator private.

6. Force-unwrap !!