kotlin java.lang.NullPointerException: null cannot be cast to non-null type androidx.navigation.frag-CodePudding

I looked at past questions but i can't still solve my problem I am getting this error : java.lang.NullPointerException: null cannot be cast to non-null type androidx.navigation.fragment.NavHostFragment

My MainActivity code is :

class MainActivity : AppCompatActivity() {




override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
    val navController =navHostFragment.navController
    val navBottomView:  BottomNavigationView = findViewById(R.id.bottomNavigation)
    navBottomView.setupWithNavController(navController)

}

} My HomeFragment code is this

class HomeFragment : Fragment() {

private var activity: MainActivity?= null



override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    activity = activity
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    val  view : View = inflater.inflate(R.layout.fragment_home,container,false)
    return view
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
}

}

ActivityMain.xml code is here too :

<RelativeLayout 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"
android:paddingTop="?attr/actionBarSize">

<FrameLayout
    android:id="@ id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_above="@id/app_bar_layout" >

    <androidx.fragment.app.FragmentContainerView
        android:id="@ id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graoh" />

</FrameLayout>
<com.google.android.material.appbar.AppBarLayout
    android:id="@ id/app_bar_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true">

    <androidx.appcompat.widget.Toolbar
        android:id="@ id/dashboard_toolbar"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@android:color/white">
        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@ id/bottomNavigation"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@android:color/white"
            app:menu="@menu/bottom_nav_menu"
            app:labelVisibilityMode="unlabeled"
            android:layout_marginRight="15dp"/>

    </androidx.appcompat.widget.Toolbar>

</com.google.android.material.appbar.AppBarLayout>

I can't run my app. If some one can help me it will be perfect

CodePudding user response：

I have a suggestion that for some reason your nav_host_fragment is not created. Try to look at your gradle, most likely the problem is in your implementation

CodePudding user response：

The problem is in the MainActivity where you do not have setContentView(R.id.activity_main)

extra notes I have noticed in your homeFragment you have: activity = activity // which is self assign

and in your main activity xml you have a typo in the following line: app:navGraph="@navigation/nav_graoh"

and you are missing the closing tag of relative layout