Stop fragment refresh in bottom nav using navhost
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
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
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
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.