Develop Reference

Error using <FragmentContainerView>, but no error with <fragment>

I am developing a mobile app and I am currently trying to rework my workflow to more appropriately leverage Activities and Fragments for their intended purposes and I have run across a strange issue I can't figure out. I have a fragment I am trying to add to an Activity, but what I try and use FragmentContainerView, the app crashes on launch, but it doesn't happen when I just use a tag with all the same attributes. In looking at the Logcat, the error comes from null being assigned to the last line of the utils file where it tries to assign to topAppBar view the view with an id of top_app_bar. Here is the relevant code:
MainActivity.kt
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
fragmentManager.beginTransaction().replace(R.id.frame_layout, HomeFragment()).commit()
utils = Utils(this)
topAppBar = findViewById(R.id.top_app_bar)
drawerLayout = findViewById(R.id.drawer_layout)
val navigationView: NavigationView = findViewById(R.id.navigation_view)
topAppBar.setNavigationOnClickListener {
if (!drawerLayout.isDrawerOpen(GravityCompat.START)) {
drawerLayout.openDrawer(GravityCompat.START)
}
else {
drawerLayout.closeDrawer(GravityCompat.START)
}
}
navigationView.setNavigationItemSelectedListener { item ->
val id: Int = item.itemId
drawerLayout.closeDrawer(GravityCompat.START)
when (id) {
R.id.navigation_home -> { utils.replaceFragment(HomeFragment(), getString(R.string.app_name)) }
R.id.navigation_recipes -> { utils.replaceActivity(this, item.title.toString().lowercase()) }
R.id.navigation_budget -> { utils.replaceActivity(this, item.title.toString().lowercase()) }
R.id.navigation_inventory -> { utils.replaceActivity(this, item.title.toString().lowercase()) }
R.id.navigation_customers -> { utils.replaceActivity(this, item.title.toString().lowercase()) }
R.id.navigation_reports -> { utils.replaceActivity(this, item.title.toString().lowercase()) }
}
true
}
activity_main.xml
<androidx.fragment.app.FragmentContainerView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/fragment_container_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.example.bakingapp.ui.TopAppBarFragment"
tools:layout="#layout/fragment_top_app_bar" />
Utils.kt (There is more to this file, but it is not relevant to the problem)
class Utils(activity: Activity) {
private var currentActivity: Activity
private var fragmentManager: FragmentManager
private var topAppBar: MaterialToolbar
val activitiesList = listOf("recipes", "budget", "inventory", "customers",
"reports")
init {
currentActivity = activity
fragmentManager = (activity as AppCompatActivity).supportFragmentManager
topAppBar = currentActivity.findViewById(R.id.top_app_bar)
}
}
This works perfectly fine when I use instead of what is currently there, but I get warnings saying I shouldn't use fragment. I should be able to use the more proper tag, but I don't understand why it can't find the view when I use this method, but it can find the view when I use the tag. If someone could explain what is happening here and what I can do to fix the issue, I would really appreciate it.

Step 1 : Add FragmentContainerView to your activity xml
<androidx.fragment.app.FragmentContainerView
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
Step 2 : In your MainActivity.class file, declare FragmentManager
private FragmentManager manager;
Step 3 : Initialize FragmentManager in onCreate()
manager = getSupportFragmentManager();
Step 4 : In your onOptionsItemSelected() begin this fragment
Bundle bundle = new Bundle();
manager.beginTransaction()
.replace(R.id.container/*Your View Id*/, YourFragment.class, bundle, "TAG")
.setReorderingAllowed(true)
//.setCustomAnimations(R.anim.anim_enter, R.anim.anim_exit)
.addToBackStack("TAG")
.commit();

Have you tried putting FragmentContainerView inside a layout? Instead of using it as parent layout.
That could solve it.

I managed to figure out the problem. It was a scope issue. A lot of logic for a Fragment I was handling in MainActivity. I moved pretty much everything in my onCreate function into the relevant Fragment file and from there was able to get the FragmentContainerView working after refactoring this code

Issue with backstack and bottomnav in kotlin

I have a bottom nav with 4 fragments Home, Following, Notification, and Profile, there is no issue with the bottom navigation on backstack , but now for eg from profile fragment I jumped to a fragment called edit_profile which is not a part of the bottom nav and when press back I want that it should go back to the profile fragment but the backstack is taking me from edit_profile to directly home fragment
here is a recording link
I recently change my project from java to kotlin and I'm a beginner in kotlin
i really like the navigation of Pinterest and Instagram
Note:- All this code is automatically changed to kotlin (with some
changes done manually ) , this issue was also with java and not after migrating to kotlin , Also if you want more reference of the code
please tell me i will update the question
Code
MainActivity.kt // Bottom Nav
class MainActivity : AppCompatActivity() {
var bottomNavigationView: BottomNavigationView? = null
var integerDeque: Deque<Int> = ArrayDeque(3)
var flag = true
#RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
setContentView(R.layout.activity_main)
val window = this.window
window.statusBarColor = this.resources.getColor(R.color.black)
bottomNavigationView = findViewById(R.id.bottom_navigation_view)
integerDeque.push(R.id.nav_home)
loadFragments(Home_Fragment())
bottomNavigationView!!.selectedItemId = R.id.nav_home
bottomNavigationView!!.setOnNavigationItemSelectedListener(
BottomNavigationView.OnNavigationItemSelectedListener { item: MenuItem ->
val id = item.itemId
if (integerDeque.contains(id)) {
if (id == R.id.nav_home) {
integerDeque.size
if (flag) {
integerDeque.addFirst(R.id.nav_home)
flag = false
}
}
integerDeque.remove(id)
}
integerDeque.push(id)
loadFragments(getFragment(item.itemId))
false
}
)
}
#SuppressLint("NonConstantResourceId")
private fun getFragment(itemId: Int): Fragment {
when (itemId) {
R.id.nav_home -> {
bottomNavigationView!!.menu.getItem(0).isChecked = true
return Home_Fragment()
}
R.id.nav_following -> {
bottomNavigationView!!.menu.getItem(1).isChecked = true
return Following_Fragment()
}
R.id.nav_notification -> {
bottomNavigationView!!.menu.getItem(2).isChecked = true
return Notification_Fragment()
}
R.id.nav_profile -> {
bottomNavigationView!!.menu.getItem(3).isChecked = true
return Profile_Fragment()
}
}
bottomNavigationView!!.menu.getItem(0).isChecked = true
return Home_Fragment()
}
private fun loadFragments(fragment: Fragment?) {
if (fragment != null) {
supportFragmentManager.beginTransaction()
.replace(R.id.fragment_container, fragment, fragment.javaClass.simpleName)
.commit()
}
}
override fun onBackPressed() {
integerDeque.pop()
if (!integerDeque.isEmpty()) {
loadFragments(getFragment(integerDeque.peek()))
} else {
finish()
}
}
Edit_Profile.kt // from this fragment i want to go back to the last fragment which should be the profile fragment
class Edit_Profile : Fragment() {
private var profilePhoto: CircleImageView? = null
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_edit_profile, container, false)
profilePhoto = view.findViewById(R.id.circleImageView)
initImageLoader()
setProfileImage()
val imageView = view.findViewById<ImageView>(R.id.backArrow)
imageView.setOnClickListener {
val newCase: Fragment = Profile_Fragment()
assert(fragmentManager != null)
val transaction = requireFragmentManager().beginTransaction()
transaction.replace(R.id.fragment_container, newCase)
transaction.addToBackStack(Profile_Fragment.toString())
transaction.commit()
}
return view
}
Edit
added a part of the transaction from Profile Fragment to Edit Profile
ProfileFragment.kt
editProfileButton!!.setOnClickListener(View.OnClickListener { v: View? ->
val edit_profile: Fragment = Edit_Profile()
requireActivity().getSupportFragmentManager()
.beginTransaction()
.add(R.id.fragment_container, edit_profile,"TAG")
.addToBackStack("TAG")
.commit()
})

Now you are managing the back stack through the integerDeque array.
When you go to a new BottomNavigationView fragment; you added its id to the array if it doesn't already exist.
When you pop up the back stack; the fragment at the top is kicked off the array.
But since you pushed all those ids in the bottomNavigationView.setOnItemSelectedListener callback; then the integerDeque array only contains BottomNavigationView fragments ids.
And as the Edit_Profile fragment is not a part of BottomNavigationView fragments, then it won't be added/popped off the queue. Instead when you try to popup the back stack whenever the Edit_Profile fragment is shown; the normal behavior you manage in the onBackPressed() continues and the Profile_Fragment id will pop up from the queue making you return to the preceding fragment (Home_Fragment) in your mentioned example.
A little fix to this is to consider adding an id into the queue when you transact to Edit_Profile fragment so that this id is popped off the queue resulting in back to Profile_Fragment fragment.
You can do that with the fragment's id in order to make sure it's unique:
editProfileButton!!.setOnClickListener(View.OnClickListener { v: View? ->
val edit_profile: Fragment = Edit_Profile()
requireActivity().getSupportFragmentManager()
.beginTransaction()
.add(R.id.fragment_container, edit_profile,"TAG")
.addToBackStack("TAG")
.commit()
(requireActivity() as MainActivity).integerDeque.push(id) // <<<< pushing id to the queue
})
This should fix your problem.
Side tips:
Use setOnItemSelectedListener instead of setOnNavigationItemSelectedListener on the BNV as the latter is deprecated.
Return true instead of false from setOnItemSelectedListener callback as this should consume the event and mark the BNV as selected.
In Edit_Profile transaction replace the fragment instead of adding it with add as already the container is consumed; and this would make you avoid overlapping fragments in the container.
In onBackPressed(); you'd replace loadFragments(..) with bottomNavigationView.selectedItemId = integerDeque.peek(); this could be lighter to reuse the same fragment instead of redoing the transaction.

Usually I follow this pattern
Where I add HomeF in main container which includes all bottom nav tab, and all bottom nav tab will open in home container, and those fragment which are not part of bottom nav will open in main container. I generally add(not replace) all the fragments in main container and set add to back stack , so that if user goes from profile (home_container) to something in main container , while backstack we can pop the top fragment and user will be seeing profile.

Android Bottom navigation with splash

I'm implementing this bottom navigation pattern but with a splash fragment.
My issue is when I navigate throw different fragments with bottom menu and I press to go back, I don't go back to the home fragment, instead of this, I return to the previous fragment.
For example, I have fragments A-B-C:
Now I'm on fragment A and I press to go to B.
Then I press to go to C (from B).
Then I press to go back.
The result is I'm getting back to B, not to fragment A (what I really want!).
(If I set in the navigation graph app:startDestination -> fragment A - instead of login fragment - everything goes well).
Here is my graph:
<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_navigation"
app:startDestination="#id/splashFragment">
<fragment
android:id="#+id/splashFragment"
android:name="application.SplashFragment"
tools:layout="#layout/fragment_splash">
<action
android:id="#+id/action_splashFragment_to_fragmentA"
app:destination="#id/fragmentA"
app:popUpTo="#id/main_navigation"
app:popUpToInclusive="true" />
</fragment>
<fragment
android:id="#+id/fragmentA"
android:name="application.fragmentA"
android:label="#string/fragmentA"
tools:layout="#layout/fragmentA" />
<fragment
android:id="#+id/fragmentB"
android:name="application.fragmentB"
android:label="fragmentB"
tools:layout="#layout/fragmentB" />
<fragment
android:id="#+id/fragmentC"
android:name="application.fragmentC"
android:label="#string/fragmentC"
tools:layout="#layout/fragmentC" />
And here my MainActivity:
class MainActivity : AppCompatActivity() {
private lateinit var appBarConfiguration: AppBarConfiguration
private lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Toolbar & Navigation
setSupportActionBar(toolbar)
navController = findNavController(R.id.nav_host)
// AppBarConfiguration with the correct top-level destinations
appBarConfiguration = AppBarConfiguration(
topLevelDestinationIds = setOf(
R.id.fragmentA,
R.id.fragmentB,
R.id.fragmentC
)
)
// This allows NavigationUI to decide what label to show in the action bar
// By using appBarConfig, it will also determine whether to
// show the up arrow or drawer menu icon
setupActionBarWithNavController(navController, appBarConfiguration)
// Set destinations to left and bottom navigation
bottom_navigation.setupWithNavController(navController)
// Set visibility for NavigationView & Toolbar
visibilityNavElements()
}
// Allows NavigationUI to support proper up navigation or the drawer layout
// drawer menu, depending on the situation
override fun onSupportNavigateUp() = navController.navigateUp(appBarConfiguration)
private fun visibilityNavElements() {
findNavController(R.id.nav_host).addOnDestinationChangedListener { _, destination, _ ->
when (destination.id) {
R.id.splashFragment -> {
toolbar.visibility = View.GONE
bottom_navigation.visibility = View.GONE
}
else -> {
toolbar.visibility = View.VISIBLE
bottom_navigation.visibility = View.VISIBLE
}
}
}
}
}
Thanks!

You can handle OnbackPress in any fragment like below and is the recommended way . You can use it in Fragment C and when back is pressed you can navigate to Fragment A
in Java
OnBackPressedCallback onBackPressedCallback = new OnBackPressedCallback(true) {
#Override
public void handleOnBackPressed() {
}
};
requireActivity().getOnBackPressedDispatcher().addCallback(this, onBackPressedCallback);
in Kotlin
val callback = requireActivity().onBackPressedDispatcher.addCallback(this) {
// Handle the back button event
}

Issues while changing Back button behavior with Navigation Drawer (Android/Kotlin)

Building my first custom app, I would like to implement something that seemed easy at first but of course it is not. I have an activity with some fragments, which I can navigate to with a Navigation Drawer:
res/menu/navdrawer_menu.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="#+id/matchFragmentUI"
android:icon="#drawable/ic_match"
android:title="#string/matches_string" />
<item
android:id="#+id/statFragmentUI"
android:icon="#drawable/ic_stat"
android:title="#string/stats_string" />
<item
android:id="#+id/clubFragmentUI"
android:icon="#drawable/ic_club"
android:title="#string/club_string" />
<item
android:id="#+id/agendaFragmentUI"
android:icon="#drawable/ic_agenda"
android:title="#string/agenda_string" />
<item
android:id="#+id/settingFragmentUI"
android:icon="#drawable/ic_settings"
android:title="#string/settings_string" />
<item
android:id="#+id/profileFragmentUI"
android:icon="#drawable/ic_person_black_24dp"
android:title="#string/profile_text" />
</menu>
res/layout/activity_content.xml
<?xml version="1.0" encoding="utf-8"?>
<layout 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">
<androidx.drawerlayout.widget.DrawerLayout
android:id="#+id/drawerLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".content.ContentActivity">
<fragment
android:id="#+id/contentNavHostFragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="#navigation/navigation_content" />
</androidx.constraintlayout.widget.ConstraintLayout>
<com.google.android.material.navigation.NavigationView
android:id="#+id/navView"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
app:menu="#menu/navdrawer_menu"
app:headerLayout="#layout/nav_header"/>
</androidx.drawerlayout.widget.DrawerLayout>
</layout>
I would like to change the back button behavior to prevent users from leaving accidentally the app like this :
/* Override behavior of back button */
override fun onBackPressed() {
/* Case we are not on the home screen */
if(/* not on home screen */) /* go to home screen */
else {
/* Otherwise we return to the access activity */
/* Dialog window to prevent accidental leaving */
val backAlertDialog = android.app.AlertDialog.Builder(this)
backAlertDialog.setTitle("Log out")
backAlertDialog.setMessage("Are you sure you want to leave?")
/* buttons YES/NO actions */
backAlertDialog.setPositiveButton("No") { dialog, which -> dialog.cancel() }
backAlertDialog.setNegativeButton("Yes") { dialog, which ->
val accessIntent = Intent(this, AccessActivity::class.java)
accessIntent.flags = FLAG_ACTIVITY_CLEAR_TOP // Clear activity backstack
startActivity(accessIntent) // Go back to access activity
finish() // Finish this activity
}
backAlertDialog.show()
}
}
My problem is checking if we are or not displaying the HomeFragment. At first, I tried with this :
if (supportFragmentManager.backstackEntryCount > 0)
But the issue here is that navigating with the navigation drawer doesn't add anything to the backstack (the backstackEntryCount stays at 0) so it won't work.
That's why I'm now trying to use NavigationView.OnNavigationItemSelectedListener interface, to add something in the backstack when an item is selected and also keep track of what is the current displayed fragment like :
/* Keep track of what the current fragment is like */
private var fragment : Fragment? = null
override fun onNavigationItemSelected(item: MenuItem): Boolean {
val itemId = item.itemId
val fm = this.supportFragmentManager
/* Clear stack */
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE)
/* Add a case for each item in the drawer */
/* For each case, always add (push) a HomeFragment and then the fragment we navigate to */
/* Then, going back will always return to Home because we cleared backstack before */
when(itemId) {
R.id.profileFragmentUI -> {
fragment = ProfileFragmentUI()
}
R.id.agendaFragmentUI -> {
fragment = AgendaFragmentUI()
}
R.id.clubFragmentUI -> {
fragment = ClubFragmentUI()
}
R.id.statFragmentUI -> {
fragment = StatFragmentUI()
}
R.id.matchFragmentUI -> {
fragment = MatchFragmentUI()
}
R.id.settingFragmentUI -> {
fragment = SettingFragmentUI()
}
}
/* Replace current fragment by the selected fragment in backstack and add home for back support */
if (fragment != null) {
fm.beginTransaction()
.add(HomeFragmentUI(), "HomeFragmentUI")
.addToBackStack("HomeFragmentUI")
.replace(R.id.contentNavHostFragment, fragment!!)
.commit()
}
return true
}
Also, here are my onCreate() and onSupportNavigateUp() methods in the activity code :
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
/* Bind layout elements at compile time to be faster at runtime */
val binding = DataBindingUtil.setContentView<ActivityContentBinding>(this, R.layout.activity_content)
val contentDrawerLayout = binding.drawerLayout
val player = intent.getParcelableExtra("player")
val navigationView = binding.navView
navigationView.setNavigationItemSelectedListener { item -> onNavigationItemSelected(item) }
/* Setup the navigation for fragments */
val navController = this.findNavController(R.id.contentNavHostFragment)
val fragmentManager = this.supportFragmentManager
/* Setup navigation bar, with drawer menu */
NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)
NavigationUI.setupWithNavController(binding.navView, navController)
fragment = HomeFragmentUI() /* To make back button work at start of navigation */
}
override fun onSupportNavigateUp(): Boolean {
val navController = this.findNavController(R.id.contentNavHostFragment)
/* Replace up button by drawer button on title screen */
return NavigationUI.navigateUp(navController, drawerLayout)
}
Now, I want to do my check like this :
if (fragment is HomeFragmentUI)
/* display dialog */
else
/* navigate back to home */
The problem now is that when I select an item in my drawer, I navigate to the good fragment, BUT the attribute fragment is still a HomeFragmentUI instance. I tried to put some logs in
onNavigationItemSelected method but they never show up.
I have no idea of why the method is never called since I defined the listener in onCreate.
Here are some links I used until now :
https://www.youtube.com/watch?v=I47Zy6JtNIU
https://www.youtube.com/watch?v=y9KYKYJJ4GY
https://guides.codepath.com/android/Fragment-Navigation-Drawer
Thank you in advance.

Android Navigation Architecture Component - Get current visible fragment

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