kotlin.TypeCastException: null cannot be cast to non-null type androidx.navigation.fragment.NavHostFragment at NavigationExtensionsKt

Question

I copied the NavigationExtensions.kt extension file from the NavigationAdvancedSample and I get this exception:

Mafaldamafeking

Hi Amir, welcome to SO. Please post the actual text of your code and exception, using correct StackOverflow markdown (instead of images). Also have a look at how to ask and how to create a minimum, reproducible example for better results when using the site. Good luck! – Discharge

You can do safe casting using as? operator. – Skep

Answer 1

UPDATE: make sure your menu item ids are the same as your navigation resource files ids

also: if you're having a problem with ItemReselectedListener Add null safety checks, your listener should be something like this:

setOnNavigationItemReselectedListener { item ->
        val newlySelectedItemTag = graphIdToTagMap[item.itemId]
        val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
                as NavHostFragment?
        val navController = selectedFragment?.navController
        // Pop the back stack to the start destination of the current navController graph
        navController?.popBackStack(
            navController.graph.startDestination, false
        )
    }

Tonsillitis

Answer 2

In my case, I forgot to add android:name="androidx.navigation.fragment.NavHostFragment" in FragmentContainerView

Atlantean

This was the solution for me too. Thanks! – Cranston

Answer 3

I also faced this probelem, the solution is actually very simple.

Make sure your menu item's id match the id of NAV_GRAPH not destinations.

I was using the same ids for menu items and destinations, but in this case, menu item should have same id as of NAV_GRAPH.

Volnay

Answer 4

I also had the same issue

Check that you have set your start destination and attached it to a fragment. in your nav graph set app:startDestination="@id/your fragment"

this should solve your problem

Robalo

Answer 5

I manage to solve this problem.

In my case, I was calling val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment before setContentView(binding.root) so I change the order of the methods and everything was Ok.

Squalene

Answer 6

I have resolved this, Actually, i set another layout for this activity in setcontentView, When I set the original layout it worked.

Ypsilanti

Same lame thing for me – Gourami

Answer 7

So for me it was that inside my navigation graph file the id I declared on

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/my_id"
    app:startDestination="@id/container">
 ....

Was not the same name as the menu item

<item
        android:id="@+id/my_idd"
        android:enabled="true"
        android:icon="@drawable/icon"
        android:title="@string/test_title" />

Changing the id to be the same for both solved the problem

Lenssen

Answer 8

can you try with this?

val selectedFragment: NavHostFragment? = fragmentManager.findFragmentByTag(newlySelectedItemTag) as NavHostFragment

Bullfinch

Won't work either cast it to a nullable type or use safe cast operator as? – Skep

then what will you do if selectedFragment is null? – Bullfinch

wrap it with if else – Bullfinch

it will throw the same exception if you try to do like this, it won't be able to cast to a non-null NavHostFragment type – Skep