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 bottom navigation control without refreshing the fragment each time they are selected. Here is what I have currently:

navigation/main.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/main"
    app:startDestination="@id/home">

    <fragment
        android:id="@+id/home"
        android:name="com.org.ftech.fragment.HomeFragment"
        android:label="@string/app_name"
        tools:layout="@layout/fragment_home" />
    <fragment
        android:id="@+id/news"
        android:name="com.org.ftech.fragment.NewsFragment"
        android:label="News"
        tools:layout="@layout/fragment_news"/>
    <fragment
        android:id="@+id/markets"
        android:name="com.org.ftech.fragment.MarketsFragment"
        android:label="Markets"
        tools:layout="@layout/fragment_markets"/>
    <fragment
        android:id="@+id/explore"
        android:name="com.org.ftech.ExploreFragment"
        android:label="Explore"
        tools:layout="@layout/fragment_explore"/>
</navigation>

activity_mail.xml:

<?xml version="1.0" encoding="utf-8"?>
<!-- Use DrawerLayout as root container for activity -->
<androidx.drawerlayout.widget.DrawerLayout
    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/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <fragment
            android:id="@+id/nav_host_fragment"
            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_constraintHorizontal_bias="0.0"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:navGraph="@navigation/main" />

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottomNavigationView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:itemIconTint="@color/nav"
            app:itemTextColor="@color/nav"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:menu="@menu/main">

        </com.google.android.material.bottomnavigation.BottomNavigationView>

    </androidx.constraintlayout.widget.ConstraintLayout>

    <com.google.android.material.navigation.NavigationView
        app:menu="@menu/main"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:id="@+id/navigationView"
        android:layout_gravity="start">
    </com.google.android.material.navigation.NavigationView>

</androidx.drawerlayout.widget.DrawerLayout>

MainActivity.kt:

class MainActivity : AppCompatActivity() {

    private var drawerLayout: DrawerLayout? = null
    private var navigationView: NavigationView? = null
    private var bottomNavigationView: BottomNavigationView? = null
    private lateinit var appBarConfiguration: AppBarConfiguration

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

        drawerLayout = findViewById(R.id.drawer_layout)
        navigationView = findViewById(R.id.navigationView)
        bottomNavigationView = findViewById(R.id.bottomNavigationView)

        val navController = findNavController(R.id.nav_host_fragment)
        appBarConfiguration = AppBarConfiguration(setOf(R.id.markets, R.id.explore, R.id.news, R.id.home), drawerLayout)

        setupActionBarWithNavController(navController, appBarConfiguration)

        findViewById<NavigationView>(R.id.navigationView)
            .setupWithNavController(navController)

        findViewById<BottomNavigationView>(R.id.bottomNavigationView)
            .setupWithNavController(navController)

    }


    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.nav_host_fragment)
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        if (item.itemId == R.id.search) {
            startActivity(Intent(applicationContext, SearchableActivity::class.java))
        }
        return super.onOptionsItemSelected(item)
    }

    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
        menuInflater.inflate(R.menu.options_menu, menu)
        return super.onCreateOptionsMenu(menu)
    }
}

In the fragment I am making a few calls to my services to fetch the data in onCreateView, when resuming the fragment I am assuming those calls will not longer be executed and the state of the fragment should be preserved.

Solution 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);
    }


}

Or You can follow Google's recommended solution: Google Link

Solution 2

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

[EDIT] The above link is broken. Found it in a forked repo

Source

• Google's Solution

Solution 3

The simple solution to stop refreshing on multiple clicks on the same navigation item could be

 binding.navView.setOnNavigationItemSelectedListener { item ->
        if(item.itemId != binding.navView.selectedItemId)
            NavigationUI.onNavDestinationSelected(item, navController)
        true
    }

where binding.navView is the reference for BottomNavigationView using Android Data Binding.

Solution 4

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

Solution 5

Quick tip, if you just want to prevent loading the already selected fragment just override setOnNavigationItemReselectedListener and do nothing, but this won't save the fragment states

binding.navBar.setOnNavigationItemReselectedListener {  }

View more solutions

Comments

[faizanjehangir]

Do I need to set the fragments in supportFragmentManager before I try to navigate between them in a listener?

[VVB]

Yeah. Set all of them in OnCreate(...) of your Activity. Make sure default is Active & rest others are Hidden

[Pavlo Ostasha]

OnViewCreated will be executed either way. It will always be called distegarding how you are using fragmentManager - classic way or via jetpack navigation.

[EpicPandaForce]

Make sure you get the references to your fragments by first checking for their existence via FindFragmentByTag, and that you track the active fragment tag using onSaveInstanceState / onCreate(Bundle)

[faizanjehangir]

Do you have some working sample that demonstrates this approach? I was looking at here and here, would these solve this problem?

[tynn]

I actually replaced the fragment navigator to only show and hide the fragments. Before I tried to do what I suggested here and it worked as well. But it was a different use-case. You could also use actions to define the behavior then.

[baskInEminence]

What if our bottom navigation View fragment keeps showing full screen fragments? Lets say 3 levels deep for that single tab. Then wouldn't you need a viewModel essentially recording which fragment the user is on? And then quickly recreate these fragments on the fly when it gets created again? Seems like a lot of work and needing to mess around with navigation stacks which is less than ideal

[baskInEminence]

Many of us are using the nav Host xml where our fragments get defined. Any suggestions on applying this solution to that newer version since we wouldn't explicitly create fragments in the activity in code directly

[Jamil Hasnine Tamim]

@baskInEminence what is you requirements? Please explain me.

[baskInEminence]

I have a navigation xml which lists all of my fragments (following latest android pattern for navigation). My activity main xml uses a androidx.navigation.fragment.NavHostFragment element with the key value (app:navGraph="@navigation/my_nav"). The main activity does not create any fragments, only minor setup. findViewById<BottomNavigationView>(R.id.bottomNavigationView‌​).setupWithNavContro‌​ller(findNavControll‌​er(R.id.fragment)). The R.id.fragment is the NavHostFragment I mentioned earlier. This latest android pattern is different from your provided solution where fragments are manually created

[Jamil Hasnine Tamim]

@baskInEminence he wants manual process. Btw if you want to more simplify please follow this link: simplifiedcoding.net/android-navigation-tutorial

[baskInEminence]

Yeah thats just a generic tutorial on how to set it up. It doesn't dive into how to ensure the fragment doesn't refresh

[baskInEminence]

Created a solution using google's recommended answer: stackoverflow.com/a/64142496/3316842

[faizanjehangir]

This is the right way to go in 2020, I am using this navigation component in my application now.

[Merve Gencer]

This doesn't work. The fragment is always null and so a new instance is created even though I used <keep_state_fragment> inside navGraph. Seemed an elegant approach, but not working :/ Besides, navController.navigatorProvider gives warning: NavController.setNavigatorProvider can only be called from within the same library group (groupId=androidx.navigation)

[ironflower]

I have followed your guide, very helpful. Unfortunately navigation works exactly the same as before, all fragments are being recreated. Any suggestions or did I misunderstood what the google solution was supposed to do.

[chitgoks]

the docs say this is the way to go. though im not really sure if it is. i tried a simple int tracking, it always resets back to its initial value instead of the incremented one. the docs itself is fairly limited it does not even provide a simple working example.

[Vikash Parajuli]

In this case you can do simply binding.navView.setOnNavigationItemReselectedListener { }

[Richard Wilson]

Please any idea on how to upgrade to multiple backstacks? stackoverflow.com/questions/68042591/…

[Aan]

Can you provide this NavigationExtensions.kt File, given link is broken

[baskInEminence]

@AnzyShQ Thank you for the comment. Found it in a forked repo. Updated Answer

[Rasoul Miri]

don't use this way, you need the update libs. see this answer stackoverflow.com/a/69325054/4797289

[baskInEminence]

@RasoulMiri Although the new alpha version may fix it, it's still an alpha release. They keep publishing a new alpha for this version every 2 weeks. Just keep that in mind when deploying alpha changes with your production code. I am happy to see Google has addressed at least looked into this matter

[Aan]

Does this implementations only stops the fragment refresh ? Seems not working. Can you provide any snippet or something working ?

[Kl3jvi]

this works, thanks

[Vasily Kabunov]

You can use navView.setOnItemReselectedListener { } instead of deprecated navView.setOnNavigationItemReselectedListener { }