Navigation Component — какво е това, NavHost и Navigation Graph

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    app:startDestination="@+id/homeFragment">

    <fragment
        android:id="@+id/homeFragment"
        android:name=".HomeFragment"
        android:label="Начало"
        tools:layout="@layout/fragment_home">
        <action
            android:id="@+id/action_home_to_detail"
            app:destination="@+id/detailFragment"
            app:enterAnim="@anim/slide_in_right"
            app:exitAnim="@anim/slide_out_left"
            app:popEnterAnim="@anim/slide_in_left"
            app:popExitAnim="@anim/slide_out_right" />
    </fragment>

    <fragment
        android:id="@+id/detailFragment"
        android:name=".DetailFragment"
        android:label="Детайли"
        tools:layout="@layout/fragment_detail">
        <argument android:name="itemId"
            app:argType="integer"
            android:defaultValue="0" />
    </fragment>
</navigation>

// Layout Activity: activity_main.xml
// <androidx.fragment.app.FragmentContainerView
//     android:id="@+id/nav_host_fragment"
//     android:name="androidx.navigation.fragment.NavHostFragment"
//     app:navGraph="@navigation/nav_graph"
//     app:defaultNavHost="true" />

class MainActivity : AppCompatActivity() {

    private val navController by lazy {
        (findViewById<NavHostFragment>(R.id.nav_host_fragment))
            .navController
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // NavigationUI свързва NavController с AppBar
        setupActionBarWithNavController(navController)
    }

    // Преход към екрана с детайли
    fun openDetail(itemId: Long) {
        val bundle = Bundle().apply {
            putLong("itemId", itemId)
        }
        navController.navigate(R.id.action_home_to_detail, bundle)
    }

    override fun onSupportNavigateUp() = 
        navController.navigateUp() || super.onSupportNavigateUp()
}

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate
        android:fromXDelta="100%"
        android:toXDelta="0%"
        android:duration="300" />
</set>

// Програмен преход с анимация
val navOptions = NavOptions.Builder()
    .setEnterAnim(R.anim.slide_in_right)
    .setExitAnim(R.anim.slide_out_left)
    .setPopEnterAnim(R.anim.slide_in_left)
    .setPopExitAnim(R.anim.slide_out_right)
    .build()

navController.navigate(R.id.detailFragment, args, navOptions)

// build.gradle (module)
plugins {
    id 'androidx.navigation.safeargs.kotlin'
}

// Safe Args генерира: DetailFragmentArgs, HomeFragmentDirections
// Използване в HomeFragment:
val action = HomeFragmentDirections
    .actionHomeToDetail(itemId = 42L)
findNavController().navigate(action)

// Използване в DetailFragment:
private val args: DetailFragmentArgs by navArgs()
// args.itemId има тип Long, null не може да бъде предаден

override fun onViewCreated(...) {
    super.onViewCreated(...)
    loadItem(args.itemId)
}

<fragment android:id="@+id/profileFragment"
    android:name=".ProfileFragment">
    <deepLink
        app:uri="https://example.com/profile/{userId}" />
    <argument
        android:name="userId"
        app:argType="string" />
</fragment>

// Програмно създаване на Deep Link
val pendingIntent = NavDeepLinkBuilder(context)
    .setGraph(R.navigation.nav_graph)
    .setDestination(R.id.profileFragment)
    .setArguments(Bundle().apply {
        putString("userId", "user_123")
    })
    .createPendingIntent()

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyAppTheme {
                val navController = rememberNavController()
                NavHost(
                    navController = navController,
                    startDestination = "home"
                ) {
                    composable("home") {
                        HomeScreen(
                            onItemClick = { id ->
                                navController.navigate("detail/$id")
                            }
                        )
                    }
                    composable(
                        route = "detail/{itemId}",
                        arguments = listOf(
                            navArgument("itemId") {
                                type = NavType.LongType
                            }
                        )
                    ) { backStackEntry ->
                        val itemId = backStackEntry
                            .arguments?.getLong("itemId") ?: 0L
                        DetailScreen(itemId = itemId)
                    }
                }
            }
        }
    }
}