Ako by ste implementovali navigáciu s tlačidlami, aby…

Používam Navigation Architecture Component.

Vytvorenie NavGraph: Definoval by som Destinácie (fragmenty alebo Activity) a Actions (prechody medzi nimi) v XML zdroji.

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/nav_graph"
    app:startDestination="@id/fragmentA"> // Počiatočný bod

    <fragment
        android:id="@+id/fragmentA"
        android:name="com.example.FragmentA"
        android:label="FragmentA" >
        <action
            android:id="@+id/action_fragmentA_to_fragmentB"
            app:destination="@id/fragmentB" />
    </fragment>
    <fragment
        android:id="@+id/fragmentB"
        android:name="com.example.FragmentB"
        android:label="FragmentB" >
        <action
            android:id="@+id/action_fragmentB_to_fragmentC"
            app:destination="@id/fragmentC" />
    </fragment>
     <fragment
        android:id="@+id/fragmentC"
        android:name="com.example.FragmentC"
        android:label="FragmentC" />
</navigation>

Umiestnenie NavHost: Pridal by som NavHost (napríklad NavHostFragment) do rozloženia aktivity, ku ktorej je pripojený NavGraph.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        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" /> // Pripojenie NavGraph

    <!-- Tu môžu byť navigačné tlačidlá -->
</LinearLayout>

Pridanie navigačných tlačidiel: Použil by som BottomNavigationView alebo samostatné tlačidlá. Pre BottomNavigationView by som ho prepojil s NavController.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        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" />

    <Button
        android:id="@+id/button_go_to_b"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Choď na B" />

    <Button
        android:id="@+id/button_go_to_c"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Choď na C" />
</LinearLayout>

Spracovanie stlačení tlačidiel v kóde: Získal by som inštanciu NavController a volal navigate() pri stlačení tlačidla. NavController automaticky spravuje back stack.

// V Activity alebo Fragment
import androidx.navigation.findNavController

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    val navController = findNavController(R.id.nav_host_fragment) // Získanie NavController

    view.findViewById<Button>(R.id.button_go_to_b).setOnClickListener {
        navController.navigate(R.id.action_fragmentA_to_fragmentB) // Prechod cez Action
    }

    view.findViewById<Button>(R.id.button_go_to_c).setOnClickListener {
        // Priamy prechod na Destination, možno použiť aj action_fragmentA_to_fragmentC, ak existuje
         navController.navigate(R.id.fragmentC)
    }
}

Pre zložitejšiu navigáciu s viacerými záložkami (BottomNavigationView, DrawerLayout) by som použil setupWithNavController().

// V Activity s BottomNavigationView
import androidx.navigation.ui.setupWithNavController
import com.google.android.material.bottomnavigation.BottomNavigationView

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

    val navController = findNavController(R.id.nav_host_fragment)
    val bottomNavView = findViewById<BottomNavigationView>(R.id.bottom_nav_view)
    bottomNavView.setupWithNavController(navController) // Prepojenie BottomNavigationView s NavController
}

Navigation Component predvolene spravuje back stack. Stlačením tlačidla "Späť" sa používateľ vráti k predchádzajúcemu destination v back stack. Na riadenie správania back stack pri navigate() možno použiť NavOptions s popUpTo.

Ako by ste implementovali navigáciu s tlačidlami, aby zachovala zásobník?