Why does my NavController cannot find an ID that I already have?

Question

Every time when I launch my app it crashes and Logcat says this:

Caused by: java.lang.IllegalArgumentException: ID does not reference a View inside this Activity

So I think this is saying ID is not found, but here's my Java file and XML file corresponding to each other. Java:

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

XML:

<com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <fragment
        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:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.285"
        app:navGraph="@navigation/mobile_navigation" />

The Logcat says failed because the java file, ID does not reference a View inside this Activity. But I clearly typed the ID: nav_host_fragment. I don't know what's wrong and when I'm inside Android Studio and it DID NOT report ANY error. Please help.

Answer 1

Navigation.findNavController relies on findViewById(), which only works after you've called setContentView() - i.e., actually added your Views to your activity.