Stop fragment refresh in bottom nav using navhost

Question

This problem has been asked a few times now, but we are in 2020 now, did anyone find a good usable solution to this yet?

I want to be able to navigate using the bott

Answer 1

Try this:

public class MainActivity extends AppCompatActivity {


    final Fragment fragment1 = new HomeFragment();
    final Fragment fragment2 = new DashboardFragment();
    final Fragment fragment3 = new NotificationsFragment();
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

        fm.beginTransaction().add(R.id.main_container, fragment3, "3").hide(fragment3).commit();
        fm.beginTransaction().add(R.id.main_container, fragment2, "2").hide(fragment2).commit();
        fm.beginTransaction().add(R.id.main_container,fragment1, "1").commit();

    }


    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    fm.beginTransaction().hide(active).show(fragment1).commit();
                    active = fragment1;
                    return true;

                case R.id.navigation_dashboard:
                    fm.beginTransaction().hide(active).show(fragment2).commit();
                    active = fragment2;
                    return true;

                case R.id.navigation_notifications:
                    fm.beginTransaction().hide(active).show(fragment3).commit();
                    active = fragment3;
                    return true;
            }
            return false;
        }
    };


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            startActivity(new Intent(MainActivity.this, SettingsActivity.class));
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


}

Answer 2

Use this snippet:

private fun attachFragment(fragmentTag: String) {
    val fragmentTransaction = supportFragmentManager.beginTransaction()
    supportFragmentManager.findFragmentByTag(fragmentTag)?.let {
        if (supportFragmentManager.backStackEntryCount == 0) return
        val currentFragmentTag = supportFragmentManager.getBackStackEntryAt(supportFragmentManager.backStackEntryCount - 1).name
        (supportFragmentManager.findFragmentByTag(currentFragmentTag) as? FragmentBase)?.let { curFrag ->
            fragmentTransaction.hide(curFrag)
        }
        fragmentTransaction.show(it)
    } ?: run {
        when (fragmentTag) {
            FragmentHome.TAG -> FragmentBase.newInstance<FragmentHome>()
            FragmentAccount.TAG -> FragmentBase.newInstance<FragmentAccount>()
            else -> null
        }?.let {
            fragmentTransaction.add(R.id.container, it, fragmentTag)
            fragmentTransaction.addToBackStack(fragmentTag)
        }
    }
    fragmentTransaction.commit()
}

You can use this pass the tag of specific fragment that you want to show now, using method attachFragment(FragmentHome.TAG)

Answer 3

If you are using Jetpack, the easiest way to solve this is using ViewModel

You have to save all valuable data and not make unnecessary database loads or network calls everytime you go to a fragment from another.

UI controllers such as activities and fragments are primarily intended to display UI data, react to user actions, or handle operating system communication, such as permission requests.

Here is when we use ViewModels

ViewModel objects are automatically retained during configuration changes so that data they hold is immediately available to the next activity or fragment instance.

So if the fragment is recreated, all your data will be there instantly instead of make another call to database or network. Its important to know that if the activity or fragment that holds the ViewModel is reacreated, you will receive the same ViewModel instance created before.

But in this case you have to specify the ViewModel to have activity scope instead of fragment scope, independently if you are using a shared ViewModel for all the fragments, or a different ViewModel for every fragment.

Here is a little example using LiveData too:

//Using KTX
val model by activityViewModels<MyViewModel>()
model.getData().observe(viewLifecycleOwner, Observer<DataModel>{ data ->
        // update UI
    })

//Not using KTX
val model by lazy {ViewModelProvider(activity as ViewModelStoreOwner)[MyViewModel::class.java]}
model.getData().observe(viewLifecycleOwner, Observer<DataModel>{ data ->
        // update UI
    })

And that's it! Google is actively working on multiple back stack support for bottom tab Navigation and claim that it'll arrive on Navigation 2.4.0 as said here and on this issue tracker if you want and/or your problem is more related to multiple back stack, you can check out those links

Remember fragments still be recreated, usually you don't change component behavior, instead, you adapt your data to them!

I leave you some useful links:

ViewModel Overview Android Developers

How to communicate between fragments and activities with ViewModels - on Medium

Restoring UI State using ViewModels - on Medium

Answer 4

If you use NavigationUI.setupWithNavController(), the NavOptions are defined for you with NavigationUI.onNavDestinationSelected(). These options include launchSingleTop and, if the menu item is not secondary, a popUpTo the root of the graph.

The problem is, that launchSingleTop still replaces the top fragment with a new one. To resolve this issue, you'd have to create your own setupWithNavController() and onNavDestinationSelected() functions. In onNavDestinationSelected() you'd just adapt the NavOptions to your needs.

Answer 5

Kotlin 2020 Google's Recommended Solution

Many of these solutions call the Fragment constructor in the Main Activity. However, following Google's recommended pattern, this is not needed.

Setup Navigation Graph Tabs

Firstly create a navigation graph xml for each of your tabs under the res/navigation directory.

Filename: tab0.xml

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/tab0"
    app:startDestination="@id/fragmentA"
    tools:ignore="UnusedNavigation">

    <fragment
        android:id="@+id/fragmentA"
        android:label="@string/fragment_A_title"
        android:name="com.app.subdomain.fragA"
    >
    </fragment>
</navigation>

Repeat the above template for your other tabs. Important all fragments and the navigation graph has an id (e.g. @+id/tab0, @+id/fragmentA).

Setup Bottom Navigation View

Ensure the navigation ids are the same as the ones specified on the bottom menu xml.

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:title="@string/fragment_A_title"
        android:id="@+id/tab0"
        android:icon="@drawable/ic_baseline_book_24"/>

    <item android:title="@string/fragment_B_title"
        android:id="@+id/tab1"
        android:icon="@drawable/ic_baseline_add_alert_24"/>

    <item android:title="@string/fragment_C_title"
        android:id="@+id/tab2"
        android:icon="@drawable/ic_baseline_book_24"/>

    <item android:title="@string/fragment_D_title"
        android:id="@+id/tab3"
        android:icon="@drawable/ic_baseline_more_horiz_24"/>

</menu>

Setup Activity Main XML

Ensure FragmentContainerView is being used and not <fragment and do not set the app:navGraph attribute. This will set later in code

<androidx.fragment.app.FragmentContainerView
      android:id="@+id/fragmentContainerView"
      android:name="androidx.navigation.fragment.NavHostFragment"
      android:layout_width="0dp"
      android:layout_height="0dp"
      app:defaultNavHost="true"
      app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@id/main_toolbar"
/>

Main Activity XML

Copy over the following Code into your main activity Kotlin file and call setupBottomNavigationBar within OnCreateView. Ensure you navGraphIds use R.navigation.whatever and not R.id.whatever

private lateinit var currentNavController: LiveData<NavController>

private fun setupBottomNavigationBar() {
  val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigationView)
  val navGraphIds = listOf(R.navigation.tab0, R.navigation.tab1, R.navigation.tab2, R.navigation.tab3)
  val controller = bottomNavigationView.setupWithNavController(
      navGraphIds = navGraphIds,
      fragmentManager = supportFragmentManager,
      containerId = R.id.fragmentContainerView,
      intent = intent
  )
  controller.observe(this, { navController ->
      val toolbar = findViewById<Toolbar>(R.id.main_toolbar)
      val appBarConfiguration = AppBarConfiguration(navGraphIds.toSet())
      NavigationUI.setupWithNavController(toolbar, navController, appBarConfiguration)
      setSupportActionBar(toolbar)
  })
  currentNavController = controller
}

override fun onSupportNavigateUp(): Boolean {
  return currentNavController?.value?.navigateUp() ?: false
}

Copy NavigationExtensions.kt File

Copy the following file to your codebase

Source

• Google's Solution

Answer 6

Try something like this

navView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener)

And

private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
    when (item.itemId) {
        R.id.home -> {
            fragmentManager.beginTransaction().hide(active).show(homeFragment).commit()
            active = homeFragment
            return@OnNavigationItemSelectedListener true
        }
        R.id.news -> {
            fragmentManager.beginTransaction().hide(active).show(newsFragment).commit()
            active = newsFragment
            return@OnNavigationItemSelectedListener true
        }
        R.id.markets -> {
            fragmentManager.beginTransaction().hide(active).show(marketsFragment).commit()
            active = marketsFragment
            return@OnNavigationItemSelectedListener true
        }
        R.id.explore -> {
            fragmentManager.beginTransaction().hide(active).show(exploreFragment).commit()
            active = exploreFragment
            return@OnNavigationItemSelectedListener true
        }
    }
    false
}