IssueTracker

Jetpack Compose release version: 1.0.3

Android Studio Build: Android Studio Arctic Fox | 2020.3.1 Patch 2 Build #AI-203.7717.56.2031.7678000, built on August 26, 2021

Kotlin version: 1.5.30

Steps to Reproduce:

1. Create a NavHost, and add it as a root composable in Activity
2. Add a lifecyle observer using Disposable effect in start destination composable
3. Lifecycle event ON_STOP is triggered for a brief moment followed by ON_START event

Please find below a code sample

class AccountActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            val navController = rememberNavController()

            SampleTheme {
                NavHost(navController, "start_route") {
                    composable("start_route") {
                        AccountContent()
                    }
                }
            }
        }
    }
}

@Composable
fun AccountContent(lifecycleOwner: LifecycleOwner = LocalLifecycleOwner.current) {
    DisposableEffect(lifecycleOwner) {

        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_START) {
                Log.d("Lifecycle", "OnStart View")
            } else if (event == Lifecycle.Event.ON_STOP) {
                Log.d("Lifecycle", "OnStop View")
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)

        onDispose {
            lifecycleOwner.lifecycle.removeObserver(observer)
        }
    }

    Column(
        modifier = Modifier
            .fillMaxSize()
            .background(MaterialTheme.colors.background)
            .wrapContentSize(Alignment.Center)
    ) {
        Text(
            text = "Account Body",
            fontWeight = FontWeight.Bold,
            modifier = Modifier.align(Alignment.CenterHorizontally),
            textAlign = TextAlign.Right,
            fontSize = 25.sp
        )
    }
}

When we run the app we get following logs for Lifecyle events which we are logging above:

2021-10-19 16:35:34.579 19885-19885/com.example.composesample D/Lifecycle: OnStart View
2021-10-19 16:35:34.580 19885-19885/com.example.composesample D/Lifecycle: OnStop View
2021-10-19 16:35:34.581 19885-19885/com.example.composesample D/Lifecycle: OnStart View

As you can see Lifecycle ON_STOP event is being triggered before triggering ON_START again. This is not a normal behaviour as it seems the view is created 2 times, and the first creation is killed and recreated again.

This issue doesn't occur if we wrap the NavHost inside a Scaffold like below

lass AccountActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            val navController = rememberNavController()

            SampleTheme {
                Scaffold {
                    NavHost(navController, "start_route") {
                        composable("start_route") {
                            AccountContent()
                        }
                    }
                }
            }
        }
    }
}

In case of above code, we only get single ON_START event and no ON_STOP event in the Lifecycle observer of start destination composable which is kinda expected behaviour. But strangely this behaviour only happens with Scaffold and not any other composable as root like Box, or Surface.

Ian, could you help triage this?

Do you have a sample project that reproduces your issue?

Hello Ian,

I have attached the sample project below.

Just run the app and check the logs with tag "Lifecyle" and observe that ON_STOP event gets fired at the beginning for some reason. Also added comment in the code what fix this behavior like I have explained above.

Let me know if you need anything else from my side or any further explanation of the issue.

This has been fixed internally and will be available in the Navigation 2.4.0-beta02 release.