I am presenting a PagingSource returned by Room ORM on a PagingDataAdapter.
The RecyclerView is present on a Fragment -- I have two such fragments. When they are switched, they stop loading the items on next page and only placehodlers are shown on scrolling.
Please view these screen captures if it isn't clear what I mean--
When I scroll without switching fragments, all the items are loaded
When I switch Fragments before scrolling all the way down, the adapter stops loading new items
Relevant pieces of code (please ask if you would like to see some other part/file) -
The Fragment:
private lateinit var recyclerView: RecyclerView
private val recyclerAdapter = CustomersAdapter(this)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
recyclerView = view.findViewById(R.id.recycler_view)
recyclerView.adapter = recyclerAdapter
recyclerView.layoutManager = LinearLayoutManager(context)
viewLifecycleOwner.lifecycleScope.launch {
viewModel.customersFlow.collectLatest { pagingData ->
recyclerAdapter.submitData(pagingData)
}
}
}
View model-
class CustomersListViewModel(application: Application, private val debtOnly: Boolean): ViewModel() {
private val db = AppDatabase.instance(application)
private val customersDao = db.customersDao()
val customersFlow = Pager(PagingConfig(20)) {
if (debtOnly)
customersDao.getAllDebt()
else
customersDao.getAll()
}.flow.cachedIn(viewModelScope)
}
After I went through your code, I found the problem FragmentTransaction.replace function and flow.cachedIn(viewModelScope)
When the activity calls the replace fragment function, the CustomerFragment will be destroyed and its ViewModel will also be destroyed (the viewModel.onCleared() is triggered) so this time cachedIn(viewModelScope) is also invalid.
I have 3 solutions for you
Solution 1: Remove .cachedIn(viewModelScope)
Note that this is only a temporary solution and is not recommended.
Because of this, instances of fragments still exist on the activity but the fragments had destroyed (memory is still leaking).
Solution 2: Instead of using the FragmentTransaction.replace function in the Main activity, use the FragmentTransaction.add function:
It does not leak memory and can still use the cachedIn function. Should be used when the activity has few fragments and the fragment's view is not too complicated.
private fun switchNavigationFragment(navId: Int) {
when (navId) {
R.id.nav_customers -> {
switchFragment(allCustomersFragment, "Customer")
}
R.id.nav_debt -> {
switchFragment(debtCustomersFragment, "DebtCustomer")
}
}
}
private fun switchFragment(fragment: Fragment, tag: String) {
val existingFragment = supportFragmentManager.findFragmentByTag(tag)
supportFragmentManager.commit {
supportFragmentManager.fragments.forEach {
if (it.isVisible && it != fragment) {
hide(it)
}
}
if (existingFragment != fragment) {
add(R.id.fragment_container, fragment, tag)
.disallowAddToBackStack()
} else {
show(fragment)
}
}
}
Solution 3: Using with Navigation Component Jetpack
This is the safest solution.
It can be created using Android Studio's template or some of the following articles.
Navigation UI
A safer way to collect flows
I tried solution 1 and 2 and here is the result:
I have a couple of fragments in my activity, each having their own Navigation Graph, they're created when the activity is created. What I want to know is how can I choose any of them to be the defaultNavHost or the PrimaryNavigationFragment after they are created?
The code below creates them and sets them as the default one, but I don't want to recreate them each time. How can I do that?
val finalHost = NavHostFragment.create(navigation)
supportFragmentManager.beginTransaction()
.replace(R.id.navFragment0, finalHost)
.setPrimaryNavigationFragment(finalHost) // this is the equivalent to app:defaultNavHost="true"
.commit()
Couldn't find the code to do what I wanted, so here's my workaround:
First remove the #setPrimaryNavigationFragment(finalHost) from fragmentManager's transaction in your Code, and/or remove app:defaultNavHost="true" from the <fragment...> in your XML.
Then create your NavHostFragments and add each of them to a HashMap:
private val navHostFragments = HashMap<Int, NavHostFragment?>()
fun createNavHosts() {
val finalHost: NavHostFragment =
NavHostFragment.create(navigationId)
.also { navHostFragments[aHandleToTheNavHost] = it }
}
Finally in onBackPressed get the navController of the proper navHost and navigate up on it:
override fun onBackPressed() {
if (navHostFragments[aHandleToTheNavHost]?.navController?.navigateUp() == false)
super.onBackPressed()
}
Note: when #navigateUp() returns false, it means there was nowhere to navigate up to. So in there you can finish the activity or anything else you may want to do.
I'm trying to move between two fragments without recreation of them so the data in the previous fragment won't disappear.
I tried to look over the internet for answers and tried for hours but without success. I looked at those links:
link 1
link 2
link 3- android developer site
After show() and hide() I also tried the AddToBackStack() but yet no success
link 4
class MainActivity : AppCompatActivity(){
private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
#Override
when (item.itemId) {
R.id.navigation_home -> {
//replaceFragment(SignInFragment())
supportFragmentManager.beginTransaction().hide(AllEventsFragment()).commit()
supportFragmentManager.beginTransaction().show(SignInFragment()).commit()
return#OnNavigationItemSelectedListener true
}
R.id.navigation_events -> {
//replaceFragment(AllEventsFragment())
supportFragmentManager.beginTransaction().hide(SignInFragment()).commit()
supportFragmentManager.beginTransaction().show(AllEventsFragment()).commit()
if (currentUser.isNotEmpty()) {
updateRecyclerView()
sign_in_error?.visibility = View.INVISIBLE
}
return#OnNavigationItemSelectedListener true
}
}
return#OnNavigationItemSelectedListener false
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportFragmentManager.beginTransaction().add(R.id.activity_main, AllEventsFragment(), "2").commit()
supportFragmentManager.beginTransaction().add(R.id.activity_main, SignInFragment(), "1").commit()
val navView: BottomNavigationView = findViewById(R.id.nav_view)
navView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener)
personInEvent = false
}
The result is overlapping fragments without an option to really navigate between them. I really tried everything I know there are some answers over the internet but none of them helped me fix my issue. I would really appreciate some help with this frustrating issue.
Before navigation:
After navigation:
supportFragmentManager.beginTransaction().hide(AllEventsFragment()).commit()
your recreating your fragments every time!
calling AllEventsFragment() is equivelant to new AllEventsFragment()
you need to instantiate them first
for example,
your code needs to be like this,
val fragment1: Fragment = SignInFragment()
val fragment2: Fragment = AllEventsFragment()
var active = fragment1
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportFragmentManager.beginTransaction().add(R.id.activity_main,fragment2 , "2").commit()
supportFragmentManager.beginTransaction().add(R.id.activity_main, fragment1, "1").commit()
val navView: BottomNavigationView = findViewById(R.id.nav_view)
navView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener)
personInEvent = false
}
inside your listener
R.id.navigation_home -> {
supportFragmentManager.beginTransaction().beginTransaction().hide(active).show(fragment1).commit();
active = fragment1;
return#OnNavigationItemSelectedListener true
}
R.id.navigation_events -> {
//replaceFragment(AllEventsFragment())
supportFragmentManager.beginTransaction().beginTransaction().hide(active).show(fragment2).commit();
active = fragment2
)
//handle rest of the cases
Take a look at architicture components, yuo can also achieve that in the old way Android - save/restore fragment state
When a fragment isnt viewable its paused or might even be destroyed use bundle to perserve data.
What you are trying to acheive could be done using two containers but you really shouldn't
Before trying the Navigation component I used to manually do fragment transactions and used the fragment tag in order to fetch the current fragment.
val fragment:MyFragment = supportFragmentManager.findFragmentByTag(tag):MyFragment
Now in my main activity layout I have something like:
<fragment
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/nav_host"
app:navGraph= "#navigation/nav_item"
android:name="androidx.navigation.fragment.NavHostFragment"
app:defaultNavHost= "true"
/>
How can I retrieve the current displayed fragment by the Navigation component?
Doing
supportFragmentManager.findFragmentById(R.id.nav_host)
returns a NavHostFragment and I want to retrieve my shown 'MyFragment`.
Thank you.
I managed to discover a way for now and it is as follows:
NavHostFragment navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host);
navHostFragment.getChildFragmentManager().getFragments().get(0);
In case of course you know it is the first fragment. I am still investigating a way without this. I agree it is not the best way but that should be something for now.
There is no way I can find to retrieve the current fragment instance. However, you can get the ID of lastly added fragment using the code below.
navController.currentDestination?.getId()
It returns the ID in navigation file. Hope this helps.
You should look the childFragmentManager primaryNavigationFragment property of your nav fragment, this is where the current displayed fragment is referenced.
val navHost = supportFragmentManager.findFragmentById(R.id.main_nav_fragment)
navHost?.let { navFragment ->
navFragment.childFragmentManager.primaryNavigationFragment?.let {fragment->
//DO YOUR STUFF
}
}
}
This seems like the cleanest solution. Update: Changed extension function to property. Thanks Igor Wojda.
1. Create the following extension
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
val FragmentManager.currentNavigationFragment: Fragment?
get() = primaryNavigationFragment?.childFragmentManager?.fragments?.first()
2. In Activity with NavHostFragment use it like this:
val currentFragment = supportFragmentManager.currentNavigationFragment
Use addOnDestinationChangedListener in activity having NavHostFragment
For Java
NavController navController= Navigation.findNavController(MainActivity.this,R.id.your_nav_host);
navController.addOnDestinationChangedListener(new NavController.OnDestinationChangedListener() {
#Override
public void onDestinationChanged(#NonNull NavController controller, #NonNull NavDestination destination, #Nullable Bundle arguments) {
Log.e(TAG, "onDestinationChanged: "+destination.getLabel());
}
});
For Kotlin
var navController :NavController=Navigation.findNavController(this, R.id.nav_host_fragment)
navController.addOnDestinationChangedListener { controller, destination, arguments ->
Log.e(TAG, "onDestinationChanged: "+destination.label);
}
this might be late but for anyone who's still looking
val currentFragment = NavHostFragment.findNavController(nav_host_fragment).currentDestination?.id
then you can do something like
if(currentFragment == R.id.myFragment){
//do something
}
note that this is for kotlin, java code should be almost the same
My requirement is to get the current visible fragment from Parent activity,my solution is
private Fragment getCurrentVisibleFragment() {
NavHostFragment navHostFragment = (NavHostFragment)getSupportFragmentManager().getPrimaryNavigationFragment();
FragmentManager fragmentManager = navHostFragment.getChildFragmentManager();
Fragment fragment = fragmentManager.getPrimaryNavigationFragment();
if(fragment instanceof Fragment ){
return fragment ;
}
return null;
}
This may help some one with same problem.
navController().currentDestination?.id
will give you your current Fragment's id where
private fun navController() = Navigation.findNavController(this, R.id.navHostFragment)
this id is the id which you have given in your Navigation Graph XML file under fragment tag. You could also compare currentDestination.label if you want.
First, you get the current fragment by id, then you can find the fragment, depending on that id.
int id = navController.getCurrentDestination().getId();
Fragment fragment = getSupportFragmentManager().findFragmentById(id);
Found working solution.
private fun getCurrentFragment(): Fragment? {
val currentNavHost = supportFragmentManager.findFragmentById(R.id.nav_host_id)
val currentFragmentClassName = ((this as NavHost).navController.currentDestination as FragmentNavigator.Destination).className
return currentNavHost?.childFragmentManager?.fragments?.filterNotNull()?.find {
it.javaClass.name == currentFragmentClassName
}
}
As per #slhddn answer and comment this is how I'm using it and retrieving the fragment id from the nav_graph.xml file:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
setSupportActionBar(findViewById(R.id.toolbar))
val navController = findNavController(this, R.id.nav_host_fragment)
ivSettingsCog.setOnClickListener {
if (navController.currentDestination?.id == R.id.updatesFragment) // Id as per set up on nav_graph.xml file
{
navController.navigate(R.id.action_updatesFragment_to_settingsFragment)
}
}
}
}
Using navigation components, I got the current displayed fragment using this line of code:
val fragment = parentFragmentManager.primaryNavigationFragment
From an Activity that uses NavHostFragment, you can use the code below to retrieve the instance of the Active Fragment.
val fragmentInstance = myNavHostFragment?.childFragmentManager?.primaryNavigationFragment
Within your activity, hosting the NavHostFragment we can write the following piece of code to fetch the instance of the currently displayed fragment
Fragment fragment = myNavHostFragment.getChildFragmentManager().findFragmentById(R.id.navHostFragmentId)
if(fragment instanceOf MyFragment) {
//Write your code here
}
Here R.id.navHostFragmentId is the resId for the NavHostFragment within your activity xml
Make :
• in some button in your fragment:
val navController = findNavController(this)
navController.popBackStack()
• In your Activity onBackPressed()
override fun onBackPressed() {
val navController = findNavController(R.id.nav_host_fragment)
val id = navController.currentDestination?.getId()
if (id == R.id.detailMovieFragment){
navController.popBackStack()
return
}
super.onBackPressed()
}
The first fragment in navhost fragment is the current fragment
Fragment navHostFragment = getSupportFragmentManager().getPrimaryNavigationFragment();
if (navHostFragment != null)
{Fragment fragment = navHostFragment.getChildFragmentManager().getFragments().get(0);}
Finally the working solution for those of you who are still searching
Actually it is very simple and you can achieve this using callback.
follow these steps:
Create a listener inside the fragment you want to get the instance from activity onCreate()
public class HomeFragment extends Fragment {
private OnCreateFragment createLIstener;
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
createLIstener.onFragmentCreated(this);
View root = inflater.inflate(R.layout.fragment_home, container, false);
//findViews(root);
return root;
}
#Override
public void onCreateOptionsMenu(#NonNull Menu menu, #NonNull MenuInflater inflater) {
super.onCreateOptionsMenu(menu, inflater);
inflater.inflate(R.menu.menu_main, menu);
}
#Override
public boolean onOptionsItemSelected(#NonNull MenuItem item) {
if (item.getItemId()==R.id.action_show_filter){
//do something
}
return super.onOptionsItemSelected(item);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
try {
createLIstener = (OnCreateFragment) context;
} catch (ClassCastException e) {
throw new ClassCastException(context.toString() + " must implement OnArticleSelectedListener");
}
}
public interface OnCreateFragment{
void onFragmentCreated(Fragment f);
}
}
Implement your listener in the host Fragment/Activity
public class MainActivity extends AppCompatActivity implements HomeFragment.OnCreateFragment {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navView = findViewById(R.id.nav_view);
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
R.id.navigation_home,
R. ----)
.build();
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
NavigationUI.setupWithNavController(navView, navController);
}
#Override
public void onFragmentCreated(Fragment f) {
if (f!=null){
H.debug("fragment created listener: "+f.getId());
f.setHasOptionsMenu(true);
}else {
H.debug("fragment created listener: NULL");
}
}
}
And that is everything you need to do the job.
Hop this help someone
The best way I could figure out with 1 fragment, Kotlin, Navigation usage:
On your layout file add the tag: "android:tag="main_fragment_tag""
<fragment
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/nav_host"
app:navGraph= "#navigation/nav_item"
android:tag="main_fragment_tag"
android:name="androidx.navigation.fragment.NavHostFragment"
app:defaultNavHost= "true"
/>
On your Activity:
val navHostFragment = supportFragmentManager.findFragmentByTag("main_fragment_tag") as NavHostFragment
val mainFragment = navHostFragment.childFragmentManager.fragments[0] as MainFragment
mainFragment.mainFragmentMethod()
Here is my solution for java
NavHostFragment navHostFragment= (NavHostFragment) getSupportFragmentManager().getFragments().get(0);
MyFragment fragment = (MyFragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
fragment.doSomething();
create extension function on Fragment Manager
inline fun <reified T : Fragment> FragmentManager.findNavFragment(hostId: Int): T? {
val navHostFragment = findFragmentById(hostId)
return navHostFragment?.childFragmentManager?.fragments?.findLast {
it is T
} as T?
}
Now simply use it by giving id of the hosting fragment and get the specified fragment
val myFragment: MyFragment? = supportFragmentManager.findNavFragment<MyFragment>(R.id.nav_host_id)
can you please check with getChildFragmentManager() call with
NavHostFragment fragment = supportFragmentManager.findFragmentById(R.id.nav_host);
MyFragment frag = (MyFragment) fragment.getChildFragmentManager().findFragmentByTag(tag);
If you need the instance of your fragment, you can go with:
(Activity) => supportFragmentManager.fragments.first().childFragmentManager.fragments.first()
It's very ugly but from there you can check if it's an instance of the fragment you want to play around with
On Androidx, I have tried many methods for finding out required fragment from NavHostFragment. Finally I could crack it with below method
public Fragment getFunctionalFragment (String tag_name)
{
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
FragmentManager navHostManager = Objects.requireNonNull(navHostFragment).getChildFragmentManager();
Fragment fragment=null;
List fragment_list = navHostManager.getFragments();
for (int i=0; i < fragment_list.size() ; i ++ )
{
if ( fragment_list.get(i) instanceof HomeFragment && tag_name.equals("frg_home")) {
fragment = (HomeFragment) fragment_list.get(i);
break;
}
}
return fragment;
}
This code works from me
NavDestination current = NavHostFragment.findNavController(getSupportFragmentManager().getPrimaryNavigationFragment().getFragmentManager().getFragments().get(0)).getCurrentDestination();
switch (current.getId()) {
case R.id.navigation_saved:
// WRITE CODE
break;
}
this might be late but may help someone later.
if you are using nested navigations you can get id like this in Kotlin
val nav = Navigation.findNavController(requireActivity(), R.id.fragment_nav_host).currentDestination
and this is one of fragments in fragment_nav_host.xml
<fragment
android:id="#+id/sampleFragment"
android:name="com.app.sample.SampleFragment"
android:label="SampleFragment"
tools:layout="#layout/fragment_sample" />
and you can check all you need like this
if (nav.id == R.id.sampleFragment || nav.label == "SampleFragment"){}
val fragment: YourFragment? = yourNavHost.findFragment()
Note: findFragment extension function is located in androidx.fragment.app package, and it's generic function
I combined Andrei Toaders answer and Mukul Bhardwajs answer with an OnBackStackChangedListener.
As an attribute:
private FooFragment fragment;
In my onCreate
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.nav_host);
FragmentManager navHostManager = Objects.requireNonNull(navHostFragment).getChildFragmentManager();
FragmentManager.OnBackStackChangedListener listener = () -> {
List<Fragment> frags = navHostManager.getFragments();
if(!frags.isEmpty()) {
fragment = (FooFragment) frags.get(0);
}
};
navController.addOnDestinationChangedListener((controller, destination, arguments) -> {
if(destination.getId()==R.id.FooFragment){
navHostManager.addOnBackStackChangedListener(listener);
} else {
navHostManager.removeOnBackStackChangedListener(listener);
fragment = null;
}
});
This way i can get a fragment, which will be displayed later on.
One even may be able to loop though frags and check multiple fragments with instanceof.
I need to do this to setup a bottom navigation view and I did it this way:
val navController = Navigation.findNavController(requireActivity(), R.id.nav_tabs_home)
val bottomNavBar: BottomNavigationView = nav_content_view
NavigationUI.setupWithNavController(bottomNavBar, navController)
The best way to achieve this is to register a fragment lifecycle callback.
As per the original question, if your NavHostFragment is defined as...
<fragment
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/nav_host"
app:navGraph= "#navigation/nav_item"
android:name="androidx.navigation.fragment.NavHostFragment"
app:defaultNavHost= "true"
/>
Then in your main activity onCreate(..)...
nav_host.childFragmentManager.registerFragmentLifecycleCallbacks(
object:FragmentManager.FragmentLifecycleCallbacks() {
override fun onFragmentViewCreated(
fm: FragmentManager, f: Fragment, v: View,
savedInstanceState: Bundle?
) {
// callback method always called whenever a
// fragment is added, or, a back-press returns
// to the start-destination
}
}
)
Other callback methods may be overridden to fit your requirements.
This solution will work in most situations
Try this:
val mainFragment = fragmentManager?.primaryNavigationFragment?.parentFragment?.parentFragment as MainFragment
or this:
val mainFragment = fragmentManager?.primaryNavigationFragment?.parentFragment as MainFragment
I'm trying to use the new navigation component. I use a BottomNavigationView with the navController : NavigationUI.setupWithNavController(bottomNavigation, navController)
But when I'm switching fragments, they are each time destroy/create even if they were previously used.
Is there a way to keep alive our main fragments link to our BottomNavigationView?
Try this.
Navigator
Create custom navigator.
#Navigator.Name("custom_fragment") // Use as custom tag at navigation.xml
class CustomNavigator(
private val context: Context,
private val manager: FragmentManager,
private val containerId: Int
) : FragmentNavigator(context, manager, containerId) {
override fun navigate(destination: Destination, args: Bundle?, navOptions: NavOptions?) {
val tag = destination.id.toString()
val transaction = manager.beginTransaction()
val currentFragment = manager.primaryNavigationFragment
if (currentFragment != null) {
transaction.detach(currentFragment)
}
var fragment = manager.findFragmentByTag(tag)
if (fragment == null) {
fragment = destination.createFragment(args)
transaction.add(containerId, fragment, tag)
} else {
transaction.attach(fragment)
}
transaction.setPrimaryNavigationFragment(fragment)
transaction.setReorderingAllowed(true)
transaction.commit()
dispatchOnNavigatorNavigated(destination.id, BACK_STACK_DESTINATION_ADDED)
}
}
NavHostFragment
Create custom NavHostFragment.
class CustomNavHostFragment: NavHostFragment() {
override fun onCreateNavController(navController: NavController) {
super.onCreateNavController(navController)
navController.navigatorProvider += PersistentNavigator(context!!, childFragmentManager, id)
}
}
navigation.xml
Use custom tag instead of fragment tag.
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto" android:id="#+id/navigation"
app:startDestination="#id/navigation_first">
<custom_fragment
android:id="#+id/navigation_first"
android:name="com.example.sample.FirstFragment"
android:label="FirstFragment" />
<custom_fragment
android:id="#+id/navigation_second"
android:name="com.example.sample.SecondFragment"
android:label="SecondFragment" />
</navigation>
activity layout
Use CustomNavHostFragment instead of NavHostFragment.
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<fragment
android:id="#+id/nav_host_fragment"
android:name="com.example.sample.CustomNavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="#+id/bottom_navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="#navigation/navigation" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/bottom_navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="#menu/navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>
Update
I created sample project. link
I don't create custom NavHostFragment. I use navController.navigatorProvider += navigator.
Update 19.05.2021 Multiple backstack
Since Jetpack Navigation 2.4.0-alpha01 we have it out of the box.
Check Google Navigation Adavanced Sample
Old answer:
Google samples link
Just copy NavigationExtensions to your application and configure by example. Works great.
After many hours of research I found solution. It was all the time right in front of us :) There is a function: popBackStack(destination, inclusive) which navigate to given destination if found in backStack. It returns Boolean, so we can navigate there manually if the controller won't find the fragment.
if(findNavController().popBackStack(R.id.settingsFragment, false)) {
Log.d(TAG, "SettingsFragment found in backStack")
} else {
Log.d(TAG, "SettingsFragment not found in backStack, navigate manually")
findNavController().navigate(R.id.settingsFragment)
}
If you have trouble passing arguments add:
fragment.arguments = args
in class KeepStateNavigator
If you are here just to maintain the exact RecyclerView scroll state while navigating between fragments using BottomNavigationView and NavController, then there is a simple approach that is to store the layoutManager state in onDestroyView and restore it on onCreateView
I used ActivityViewModel to store the state. If you are using a different approach make sure you store the state in the parent activity or anything which survives longer than the fragment itself.
Fragment
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
recyclerview.adapter = MyAdapter()
activityViewModel.listStateParcel?.let { parcelable ->
recyclerview.layoutManager?.onRestoreInstanceState(parcelable)
activityViewModel.listStateParcel = null
}
}
override fun onDestroyView() {
val listState = planet_list?.layoutManager?.onSaveInstanceState()
listState?.let { activityViewModel.saveListState(it) }
super.onDestroyView()
}
ViewModel
var plantListStateParcel: Parcelable? = null
fun savePlanetListState(parcel: Parcelable) {
plantListStateParcel = parcel
}
I've used the link provided by #STAR_ZERO and it works fine. For those who having problem with the back button, you can handle it in the activity / nav host like this.
override fun onBackPressed() {
if(navController.currentDestination!!.id!=R.id.homeFragment){
navController.navigate(R.id.homeFragment)
}else{
super.onBackPressed()
}
}
Just check whether current destination is your root / home fragment (normally the first one in bottom navigation view), if not, just navigate back to the fragment, if yes, only exit the app or do whatever you want.
Btw, this solution need to work together with the solution link above provided by STAR_ZERO, using keep_state_fragment.
Super easy solution for custom general fragment navigation:
Step 1
Create a subclass of FragmentNavigator, overwrite instantiateFragment or navigate as you need. If we want fragment only create once, we can cache it here and return cached one at instantiateFragment method.
Step 2
Create a subclass of NavHostFragment, overwrite createFragmentNavigator or onCreateNavController, so that can inject our customed navigator(in step1).
Step 3
Replace layout xml FragmentContainerView tag attribute from android:name="com.example.learn1.navigation.TabNavHostFragment" to your customed navHostFragment(in step2).
In the latest Navigation component release - bottom navigation view will keep track of the latest fragment in stack.
Here is a sample:
https://github.com/android/architecture-components-samples/tree/main/NavigationAdvancedSample
Example code
In project build.gradle
dependencies {
classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.0-alpha01"
}
In app build.gradle
plugins {
id 'com.android.application'
id 'kotlin-android'
id 'androidx.navigation.safeargs'
}
dependencies {
implementation "androidx.navigation:navigation-fragment-ktx:2.4.0-alpha01"
implementation "androidx.navigation:navigation-ui-ktx:2.4.0-alpha01"
}
Inside your activity - you can setup navigation with toolbar & bottom navigation view
val navHostFragment = supportFragmentManager.findFragmentById(R.id.newsNavHostFragment) as NavHostFragment
val navController = navHostFragment.navController
//setup with bottom navigation view
binding.bottomNavigationView.setupWithNavController(navController)
//if you want to disable back icon in first page of the bottom navigation view
val appBarConfiguration = AppBarConfiguration(
setOf(
R.id.feedFragment,
R.id.favoriteFragment
)
).
//setup with toolbar back navigation
binding.toolbar.setupWithNavController(navController, appBarConfiguration)
Now in your fragment, you can navigate to your second frgment & when you deselect/select the bottom navigation item - NavController will remember your last fragment from the stack.
Example: In your Custom adapter
adapter.setOnItemClickListener { item ->
findNavController().navigate(
R.id.action_Fragment1_to_Fragment2
)
}
Now, when you press back inside fragment 2, NavController will pop fragment 1 automatically.
https://developer.android.com/guide/navigation/navigation-navigate
Not available as of now.
As a workaround you could store all your fetched data into ViewModel and have that data readily available when you recreate the fragment. Make sure you get the ViewModel object using activity context.
You can use LiveData to make your data lifecycle-aware observable data holder.
The solution provided by #piotr-prus helped me, but I had to add some current destination check:
if (navController.currentDestination?.id == resId) {
return //do not navigate
}
without this check current destination is going to recreate if you mistakenly navigate to it, because it wouldn't be found in back stack.