Bottom Navigation View

<?xml version="1.0" encoding="utf-8"?>
<!-- item ids = destination ids in nav_graph.xml, so setupWithNavController() can link them -->
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/notesFragment" android:icon="@drawable/ic_note" android:title="@string/menu_notes" />
    <item android:id="@+id/subjectsFragment" android:icon="@drawable/ic_subject" android:title="@string/menu_subjects" />
    <item android:id="@+id/statsFragment" android:icon="@drawable/ic_stats" android:title="@string/menu_stats" />
</menu>

<!-- activity_main.xml (Student Diary, part) -->
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNav"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:menu="@menu/bottom_nav_menu" />
</LinearLayout>

// MainActivity.onCreate (Student Diary)
val navHost = supportFragmentManager.findFragmentById(R.id.nav_host) as NavHostFragment
navController = navHost.navController

binding.bottomNav.setupWithNavController(navController)    // tap item → navigate to same id

// top-level destinations: no ← arrow on these
appBarConfiguration = AppBarConfiguration(
    setOf(R.id.notesFragment, R.id.subjectsFragment, R.id.statsFragment /* … */),
    binding.drawerLayout
)
setupActionBarWithNavController(navController, appBarConfiguration)

val bottomScreens = setOf(R.id.notesFragment, R.id.subjectsFragment, R.id.statsFragment)
navController.addOnDestinationChangedListener { _, destination, _ ->
    binding.bottomNav.isVisible = destination.id in bottomScreens
    if (destination.id == R.id.notesFragment) binding.fab.show() else binding.fab.hide()
}

// show "3" on the Notes tab (e.g. pending notes)
viewModel.countAll.observe(this) { total ->
    val badge = binding.bottomNav.getOrCreateBadge(R.id.notesFragment)
    badge.isVisible = total > 0
    badge.number = total
}
// remove it
binding.bottomNav.removeBadge(R.id.notesFragment)

// Tapping the current tab again → scroll the list to the top
binding.bottomNav.setOnItemReselectedListener { item ->
    if (item.itemId == R.id.notesFragment) scrollNotesToTop()
}

// Without the Navigation Component (manual fragments)
binding.bottomNav.setOnItemSelectedListener { item ->
    val fragment = when (item.itemId) {
        R.id.notesFragment -> NotesFragment()
        R.id.subjectsFragment -> SubjectsFragment()
        else -> StatsFragment()
    }
    supportFragmentManager.commit { replace(R.id.container, fragment) }
    true
}