Jetpack Compose + Navigation - Nested navigation with BottomNavBar

Question

I'm trying to implement the following screen flow using Jetpack Compose + Jetpack Navigation:

Actually, i am able to code two singles cases:

SplashScreen --> HomeScreen (with no BottomNavBar)
HomeScreen (with BottomNavBar) --> Tabs

I'm not able to code the whole problem. In fact, i have an issue with the management of the NavHost. In the first case (SplashScreen -> HomeScreen) i need to call the NavHost at a high scope:

class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContent {
        MyAppTheme {
            //init the Navigation Controller for screen navigation
            val navController = rememberNavController()

            //setup the Navigation Graph
            SetupNavGraph(navController)

while in the second case i need to call it in the innerPadding scope of the Scaffold composable:

fun MainScreen(navController: NavHostController) {

    Scaffold(
        bottomBar = {
            BottomNavBar(navController)
        }
    ) { //innerPadding scope
        //setup the Navigation Graph
        SetupNavGraph(navController)
    }
}

Please assume that SetupNavGraph() function works as intended (call NavHost to generate the navigation tree)

I tried to use two NavHost without success.
If i setup the NavHost in setContent() i'm able to load the splashscreen and move to an empty BottomNavBar screen. If i click on the BottomNavElements i'm able to navigate to the child tabs (in the example above "Favorite","Music","Places", "News") but the BottomNavBar disappears
I cannot setup NavHost in the innerPadding scope because this is loaded only after switching to the main screen (in the example above "Favorite Tab" + BottomBarNav)

The only workaround i found is generating the BottomNavBar composable in each of the BottomNav child tabs, but this generates a visible transition effect that i would like to avoid and, generally, doesn't seem a good practice.

Sorry and thx for editing. I added a more complete explanation and an example image of what i would like to achieve. Even if you can't answer, for the sake of being clear, could you tell me if what i ask is now understandable? Thx! — Frax
– Frax, Commented Feb 11, 2022 at 8:05

Dharman · Accepted Answer · 2022-02-11 15:59:25Z

11

Ok, i found a solution. This are the steps to achieve the desired result:

Create two different NavGraph, one for Splash->MainScreen and the other for the BottomNavBar

const val ROOT_ROUTE = "root"

@Composable
fun SetupRootNavGraph(navController: NavHostController) {
    NavHost(
        navController = navController,
        startDestination = Screen.FirstScreen.route,
        route = ROOT_ROUTE
    ) {
        composable(Screen.FirstScreen.route) { FirstScreen(navController)}
        composable(Screen.SecondScreen.route) { MainScreen(navController)}
    }
}

const val BOTTOM_BAR_ROUTE = "bottomBar"

@Composable
fun SetupNavGraphBottomBar(navController: NavHostController) {
    NavHost(
        navController = navController,
        startDestination = BottomBarScreen.FirstElement.route,
        route = BOTTOM_BAR_ROUTE
    ) {
        composable(BottomBarScreen.FirstElement.route) { FirstElementScreen() }
        composable(BottomBarScreen.SecondElement.route) { SecondElementScreen() }
        composable(BottomBarScreen.ThirdElement.route) { ThirdElementScreen() }
    }
}

Init the NavController and the RootNavGraph after setContent() in your MainActivity. This will be in charge of the SplashScreen -> MainScreen navigation tree.

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyAppTheme {

                //init the Navigation Controller for screen navigation
                val navController = rememberNavController()

                //setup the Root Navigation Graph
                SetupRootNavGraph(navController)
            }
        }
    }
}

Re-init the NavController in the Screen where you have your BottomNavBar ("MainScreen" in the example) and the assign to it the BottomNavGraph in the innerPadding scope.

@Composable
fun MainScreen(navController: NavHostController) {

    //Re-initialize the NavController to set a new NavGraph
    val navControllerBottomBar = rememberNavController()

    Scaffold(
        bottomBar = {
            BottomNavBar(navControllerBottomBar)
        }
    ) {
        //setup the Navigation Graph
        SetupNavGraphBottomBar(navControllerBottomBar, user)
    }
}

And this will work like charm! Of course you will need to structure your BottomNavBar in order to manage the navigation as documented on Official docs

edited Feb 11, 2022 at 15:59

Dharman♦

33.9k27 gold badges103 silver badges157 bronze badges

answered Feb 11, 2022 at 15:53

Frax

4575 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

AkshayT Over a year ago

Question: Your MainScreen is part of which Graph? ROOT_ROUTE or BOTTOM_BAR_ROUTE ?

Frax Over a year ago

You found me at the end. :) It's root route. Btw, I suggest you to read another similar post. This solution is not the best if you have that a tab of the bottomnav need to navigate to a screen without bottomnav.

Frax Over a year ago

stackoverflow.com/questions/71395630/… this is the post I suggest you to read

lostintranslation Over a year ago

But you lose the ability to navigate between the two graphs right? How do you go from the BottomNavGraph back to the MainNavGraph. EG if the main graph was a login flow, when your session expires one would want to navigate from the bottom graph back to the main graph

Frax Over a year ago

You are absolutely right. Unfortunately I was not able to find a solution with nested navigation. I prefer the solution in the other post (the other one you commented) because is more consistent and organized, even if it's still more a workaround than a solution

Collectives™ on Stack Overflow

Jetpack Compose + Navigation - Nested navigation with BottomNavBar

1 Answer 1

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related