Fix fragment container view crash

see https://issuetracker.google.com/issues/142847973

Author: daniel-stoneuk

app/src/main/java/guide/graphql/toc/MainActivity.kt

@@ -2,29 +2,37 @@ package guide.graphql.toc
 
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
-import androidx.navigation.findNavController
+import androidx.navigation.NavController
+import androidx.navigation.fragment.NavHostFragment
 import androidx.navigation.ui.NavigationUI
 import guide.graphql.toc.databinding.ActivityMainBinding
 
+
 class MainActivity : AppCompatActivity() {
 
     private lateinit var binding: ActivityMainBinding
+    private lateinit var navController: NavController
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
         binding = ActivityMainBinding.inflate(layoutInflater)
 
+        val navHostFragment = supportFragmentManager
+            .findFragmentById(R.id.nav_host_fragment) as NavHostFragment?
+
+        navController = navHostFragment!!.navController
+
         setContentView(binding.root)
         setSupportActionBar(binding.toolbar)
 
         NavigationUI.setupActionBarWithNavController(
             this,
-            findNavController(R.id.nav_host_fragment)
+            navController
         )
     }
 
     override fun onSupportNavigateUp(): Boolean {
-        return findNavController(R.id.nav_host_fragment).navigateUp() || super.onSupportNavigateUp()
+        return navController.navigateUp() || super.onSupportNavigateUp()
     }
 }

app/src/main/java/guide/graphql/toc/ui/chapters/ChaptersViewModel.kt

@@ -2,7 +2,6 @@ package guide.graphql.toc.ui.chapters
 
 import android.util.Log
 import androidx.lifecycle.LiveData
-import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.liveData
 import com.apollographql.apollo.coroutines.toDeferred

app/src/main/res/layout/activity_main.xml

@@ -23,7 +23,7 @@
             android:theme="@style/AppTheme.Toolbar" />
     </com.google.android.material.appbar.AppBarLayout>
 
-    <fragment
+    <androidx.fragment.app.FragmentContainerView
         android:id="@+id/nav_host_fragment"
         android:name="androidx.navigation.fragment.NavHostFragment"
         android:layout_width="match_parent"