How to Fix Mainactivity Does Not Have a Navcontroller

IllegalStateException: Link does not have a NavController set

UPDATED SOLUTION

Actually, Navigation can't find NavController in FrameLayout. So replacing <FrameLayout> with <fragment> will make it work.

Add the following inside the <fragment> tag -

android:name="androidx.navigation.fragment.NavHostFragment"

After doing the changes, the code will look similar to this -

 <fragment
       android:id="@+id/fragment_container"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       app:layout_behavior="@string/appbar_scrolling_view_behavior"
       android:name="androidx.navigation.fragment.NavHostFragment"
       app:navGraph="@navigation/main_navigation"
       app:defaultNavHost="true"/>

Main Activity does not have a NavController

As it was described in the reference:

When creating the NavHostFragment using FragmentContainerView or if
manually adding the NavHostFragment to your activity via a
FragmentTransaction, attempting to retrieve the NavController in
onCreate() of an Activity via Navigation.findNavController(Activity,
@IdRes int) will fail. You should retrieve the NavController directly
from the NavHostFragment instead.

Looks like you should use

NavHostFragment navHostFragment =
        (NavHostFragment) supportFragmentManager.findFragmentById(R.id.nav_host_fragment);
NavController navController = navHostFragment.getNavController();

instead of

 NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_activity_main);

How do I fix error java.lang.IllegalStateException: Activity does not have a NavController...?

--------- Answer -----------

Follow the steps below:

    private val navHostFragment =  supportFragmentManager
        .findFragmentById(R.id.activity_main_nav_host_fragment) as NavHostFragment
   
     navController = navHostFragment.navController

After this you can use navcontroller.

Feel free to ask if something is unclear.

Activity does not have a NavController set on

You can get the Nav Controller using Java like this:

final NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
final NavController navController = navHostFragment.getNavController();

And then you setup your bottom navigation like this:

NavigationUI.setupWithNavController(bottomNavigationView, navController);

Kotlin: does not have a NavController set

I had the same issue a while back. It works everywhere except in onCreate. In onCreate I had to find it like so:

val navigationHost =
            supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
val navController = navigationHost.navController

Navigation Component, does not have a NavController set , does not have a NavController set at androidx.navigation.Navigation.findNavController

Solution 1)

You need to check if fragment is visible or not anymore before onFinish() get called

Add a boolean , initialize it in onResume() and make it false in onPause() like this

private boolean isFragmentVisible=false;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_loading, container, false);
}



@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    this.view = view;

    new CountDownTimer(5000, 1000) { //Wait 5 seconds
        public void onTick(long millisUntilFinished) {
        }

        public void onFinish() { // Then navigate to other page.

           //check if fragment is visible or not
        if(isFragmentVisible){
          navigate();
        }
            
        }
    }.start();

    super.onViewCreated(view, savedInstanceState);
}

  @Override
    public void onResume() {
        super.onResume();
         isFragmentVisible=true;
    }

    @Override
    public void onPause() {
        super.onPause();
        isFragmentVisible=false;
    }
private void navigate() { 
  Navigation.findNavController(this.view).navigate(LoadingFragmentDirections.actionLoadingFragmentToSignInPagerFragment());
}**

Solution 2)
You need to declare an instance of CountDownTimer and initialize it once and make it null when fragment is no more visible

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