CompositionLocal in Jetpack Compose

Example.kt

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContent {
            MaterialTheme {
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
                    var analyticsProvider by remember { mutableStateOf<Analytics.Provider>(Analytics.Provider.Firebase) }
                    CompositionLocalProvider(LocalAnalytics provides Analytics(analyticsProvider)) {
                        Greeting(modifier = Modifier.padding(innerPadding))
                    }
                }
            }
        }
    }
}

@Composable
fun Greeting(modifier: Modifier = Modifier) {
    val analytics = LocalAnalytics.current
    analytics.trackEvent("Greeting (Re)composed")
    Text(
        modifier = modifier,
        text = "Hello World!"
    )
}


data class Analytics(private val provider: Provider) {

    sealed interface Provider {
        object LogCat : Provider
        object Println : Provider
        object Firebase : Provider
    }

    fun trackEvent(eventName: String) {
        when (provider) {
            Provider.LogCat -> println("Debug: LogCat - Tracking event: $eventName")
            Provider.Println -> println("Debug: Println - Tracking event: $eventName")
            Provider.Firebase -> println("Debug: Firebase - Tracking event: $eventName")
        }
    }
}

val LocalAnalytics = compositionLocalOf { Analytics(Analytics.Provider.Println) }

NestedTracking.kt

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContent {
            MaterialTheme {
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
                    var analyticsProvider by remember { mutableStateOf<Analytics.Provider>(Analytics.Provider.Firebase) }
                    CompositionLocalProvider(
                        LocalAnalytics provides Analytics(analyticsProvider, "main")
                    ) {
                        Column(Modifier.padding(innerPadding)) {
                            RadioButton(
                                text = "Println",
                                selected = analyticsProvider is Analytics.Provider.Println,
                                onClick = { analyticsProvider = Analytics.Provider.Println }
                            )
                            RadioButton(
                                text = "LogCat",
                                selected = analyticsProvider is Analytics.Provider.LogCat,
                                onClick = { analyticsProvider = Analytics.Provider.LogCat }
                            )
                            RadioButton(
                                text = "Firebase",
                                selected = analyticsProvider is Analytics.Provider.Firebase,
                                onClick = { analyticsProvider = Analytics.Provider.Firebase }
                            )

                            TrackableButton("0. View")
                            Column {
                                CompositionLocalProvider(
                                    LocalAnalytics provides
                                            LocalAnalytics.current.wrapWithPrefix("view1")
                                ) {
                                    TrackableButton("1. View")
                                    Column {
                                        CompositionLocalProvider(
                                            LocalAnalytics provides
                                                    LocalAnalytics.current.wrapWithPrefix("view2")
                                        ) {
                                            TrackableButton("2. View")
                                            Column {
                                                CompositionLocalProvider(
                                                    LocalAnalytics provides
                                                            LocalAnalytics.current.wrapWithPrefix("view3")
                                                ) {
                                                    TrackableButton("3. View")
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

@Composable
fun RadioButton(
    text: String,
    selected: Boolean,
    onClick: () -> Unit,
) {
    Row {
        androidx.compose.material3.RadioButton(
            selected = selected,
            onClick = onClick
        )
        Text(
            text = text,
            modifier = Modifier
                .padding(start = 8.dp)
                .align(Alignment.CenterVertically)
        )
    }
}

@Composable
fun TrackableButton(text: String) {
    val analytics = LocalAnalytics.current
    val context = LocalContext.current
    analytics.trackEvent("TrackableButton (Re)composed")
    Button(
        onClick = {
            analytics.trackEvent("buttonClicked")
            Toast.makeText(context, "Button at $text clicked", Toast.LENGTH_SHORT).show()
        },
        content = { Text(text) }
    )
}

data class Analytics(private val provider: Provider, private val eventNamePrefix: String) {

    sealed interface Provider {
        object LogCat : Provider
        object Println : Provider
        object Firebase : Provider
    }

    fun trackEvent(eventName: String) {
        when (provider) {
            Provider.LogCat -> println("Debug: LogCat - Tracking event: ${eventNamePrefix + "_" + eventName}")
            Provider.Println -> println("Debug: Println - Tracking event: ${eventNamePrefix + "_" + eventName}")
            Provider.Firebase -> println("Debug: Firebase - Tracking event: ${eventNamePrefix + "_" + eventName}")
        }
    }

    fun wrapWithPrefix(appendPrefix: String): Analytics =
        copy(eventNamePrefix = eventNamePrefix + "_" + appendPrefix)
}

val LocalAnalytics = compositionLocalOf { Analytics(Analytics.Provider.Println, "null") }