IssueTracker

Jetpack Compose version: Bom 2024.11.00

Jetpack Compose component(s) used: runtime and ui

Android Studio Build: Any

Kotlin version: 1.9.0

If you update some state via a LaunchedEffect and that state is a condition for some other part of the code, it is possible to reach code that should be inaccessible.

This is a simplier version of this issue with PredictiveBackHandler which updates it's enabled state as part of a LaunchedEffect.

This is the code (project also attached):

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContent {
            var state by remember { mutableIntStateOf(2) }
            val conditionalCallback = ConditionalCallback(state > 1) {
                Toast.makeText(this, "Fired the callback", Toast.LENGTH_SHORT).show()
                if (state < 2) {
                    error("Should not get here if state is not enabled")
                }
            }
            MyCallback(state > 1, conditionalCallback)
            Box(Modifier.padding(100.dp)) {
                Column {
                    Button(onClick = { state-- }) {
                        Text(text = "decrement state")
                    }
                    Button({ conditionalCallback.triggerCallback() }) {
                        Text(text = "trigger callback")
                    }
                    Text(text = "current State is $state")
                }
            }
        }
    }
}

@Composable
fun MyCallback(valid: Boolean, conditionalCallback: ConditionalCallback) {
    LaunchedEffect(valid) {
        conditionalCallback.isEnabled = valid
    }
}

class ConditionalCallback(var isEnabled: Boolean, private var callback: () -> Unit) {
    fun triggerCallback() {
        if (isEnabled) {
            callback.invoke()
        }
    }
}

Instead of attempting to be fast enough to trigger it manually, you can trigger the error by using the debugger.

Steps to Reproduce or Code Sample to Reproduce:

1. Launch app in debug mode \
2. Click the trigger callback button to ensure the callback fires (should see a toast)
3. Pause debugger
4. Click decrement state button once and then click the trigger callback button
5. Resume debugger
6. App crashes with bad state

If a LaunchedEffect is not be the right approach for this, is there some other component that fits better?