MainActivity.kt

package com.example.deletemenavigation

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Column
import androidx.compose.material.*
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.List
import androidx.compose.material.icons.filled.Settings
import androidx.compose.runtime.*
import androidx.compose.runtime.savedinstancestate.savedInstanceState
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.vector.ImageVector
import androidx.compose.ui.platform.setContent
import androidx.navigation.NavController
import androidx.navigation.NavHostController
import androidx.navigation.compose.*
import com.example.deletemenavigation.ui.DeleteMeNavigationTheme

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            DeleteMeNavigationTheme {
                MyAppContent()
            }
        }
    }
}

sealed class TabItem(val route: String, val title: String, val icon: ImageVector) {
    object ListInfo : TabItem("tab1", "Items", Icons.Filled.List)
    object ProfileInfo : TabItem("tab2", "Profile", Icons.Filled.Settings)
}

@Composable
fun MyAppContent() {
    var currentTab by savedInstanceState { TabItem.ListInfo.route }
    val items = listOf(
        TabItem.ListInfo,
        TabItem.ProfileInfo,
    )
    Scaffold(
        bottomBar = {
            BottomNavigation {
                items.forEach { tabItem ->
                    BottomNavigationItem(
                        icon = { Icon(tabItem.icon) },
                        label = { Text(tabItem.title) },
                        selected = tabItem.route == currentTab,
                        onClick = {
                            currentTab = tabItem.route
                        }
                    )
                }
            }
        }
    ) {
        TabContent(currentTab) { currentTab = TabItem.ListInfo.route }
    }
}

@Composable
fun TabContent(tabItem: String, onBackPressed: () -> Unit) {
    val tab1NavState =
        savedInstanceState { Bundle() }
    val tab2NavState =
        savedInstanceState { Bundle() }

    when (tabItem) {
        TabItem.ListInfo.route -> {
            TabWrapper(tab1NavState) { navController ->
                TabList(navController)
            }
        }
        TabItem.ProfileInfo.route -> {
            TabWrapper(tab2NavState) { navController ->
                TabProfile(navController, onBackPressed)
            }
        }
    }
}

@Composable
fun TabWrapper(
    navState: MutableState<Bundle>,
    content: @Composable (NavHostController) -> Unit
) {
    val navController = rememberNavController()
    onCommit {
        val callback = NavController.OnDestinationChangedListener { navController, _, _ ->
            navState.value = navController.saveState() ?: Bundle()
        }
        navController.addOnDestinationChangedListener(callback)
        navController.restoreState(navState.value)

        onDispose {
            navController.removeOnDestinationChangedListener(callback)
            navController.enableOnBackPressed(false)
        }
    }
    content(navController)
}

@Composable
fun TabList(navController: NavHostController) {
    NavHost(navController = navController, startDestination = "list") {
        composable("list") { ListScreen(navController) }
        composable("list_details") { DetailScreen() }
    }
}

@Composable
fun TabProfile(navController: NavHostController, onBackPressed: () -> Unit) {
    NavHost(navController = navController, startDestination = "profile") {
        composable("profile") { ProfileScreen(navController, onBackPressed) }
        composable("profile_details") { ProfileDetailScreen() }
    }
}

@Composable
fun ListScreen(navController: NavHostController) {
    Column(modifier = Modifier.background(Color.Red)) {
        Text(text = "Tab 1")
        Button(onClick = {
            navController.navigate("list_details")
        }) {
            Text("Next")
        }
    }
}

@Composable
fun DetailScreen() {
    Text(text = "Tab 1 - Details")
}

@Composable
fun ProfileScreen(navController: NavHostController, onBackPressed: () -> Unit) {
    Column(modifier = Modifier.background(Color.Blue)) {
        Text(text = "Tab 2")
        Button(onClick = {
            navController.navigate("profile_details")
        }) {
            Text("Next")
        }
    }
    BackButtonHandler(onBackPressed = {
        onBackPressed()
    })
}

@Composable
fun ProfileDetailScreen() {
    Text(text = "Tab 2 - Details")
}