IssueTracker

Component used: Navigation Version used: 2.8.0-beta04 Devices/Android versions reproduced on: all

Duplicate destinations in a navigation graph are allowed but can lead to indeterminate behavior at run time. Consider the following code which creates two nested nav graphs that share a destination: DetailRoute.

@Serializable data object HomeNavRoute
@Serializable data object HomeRoute
@Serializable data object ListNavRoute
@Serializable data object ListRoute 
@Serializable data class DetailRoute(val id: Int)

@Composable
fun MyNavHost(navController: NavHostController) {
    Column(modifier = Modifier.fillMaxHeight()) {
        NavHost(
            navController = navController,
            startDestination = HomeNavRoute
        ) {
            navigation<ListNavRoute>(startDestination = ListRoute) {
                composable<ListRoute> {
                    ListScreen(onClickItem = { 
                        navController.navigate(route = DetailRoute(id = 123)) 
                    })
                }
                composable<DetailRoute> { backStackEntry -> 
                    DetailScreen(
                        id = backStackEntry.toRoute<DetailRoute>().id,
                        parent = backStackEntry.destination.parent) 
                }
            }
            navigation<HomeNavRoute>(startDestination = HomeRoute) {
                composable<HomeRoute> {
                    HomeScreen(onClickItem = {
                        navController.navigate(route = DetailRoute(id = 456))
                    })
                }
                composable<DetailRoute> { backStackEntry ->
                    DetailScreen(
                        id = backStackEntry.toRoute<DetailRoute>().id,
                        parent = backStackEntry.destination.parent)
                }
            }
        }
    }
}

@Composable
private fun HomeScreen(onClickItem: () -> Unit) {
    Column {
        Text("Home screen")
        Button(onClick = onClickItem){
            Text("Go to detail screen")
        }
    }
}

@Composable
fun ListScreen(onClickItem: () -> Unit){
    Column {
        Text("I am a list screen")
        Button(onClick = onClickItem){
            Text("Go to detail screen")
        }
    }
}

@Composable
fun DetailScreen(id: Int, parent: NavDestination? = null) {
    Text("I am a detail screen with ID $id, my parent is $parent")
}

If you navigate from ListRoute to DetailRoute it is undetermined whether the resulting destination will have a parent of HomeNavRoute or ListNavRoute. If we follow the rule of "whichever destination is defined first in the navigation graph will be used" then destination with parent ListNavRoute should be used, however, in my tests, DetailRoute's parent is HomeNavRoute (which is defined second in the nav graph).

Perhaps adding a duplicate destination should be a compile-time error or warning.