kotlin.TypeCastException: null cannot be cast to non-null type android.support.v7.widget.Toolbar

Question

I'm new to Android here. What can be the situation for my problem? I'm trying to present my fragment to the MainActivity. Any suggestions will help. Thanks

Main Activity Class...

class NavigationActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.fragment_schedule)

        val toolbar = findViewById(R.id.toolbar) as Toolbar
        setSupportActionBar(toolbar) // setup toolbar
        toolbar.setNavigationIcon(R.drawable.ic_map)

        val drawer = findViewById(R.id.drawer_layout) as DrawerLayout
        val toggle = ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close)
        drawer.addDrawerListener(toggle) // navigation drawer
        toggle.syncState()

        val navigationView = findViewById(R.id.nav_view) as NavigationView
        navigationView.setNavigationItemSelectedListener(this) //setup navigation view

}

My Fragment Class..

 class fragment_schedule : Fragment() {
 override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
   // Inflate the layout for this fragment
   return inflater!!.inflate(R.layout.fragment_schedule, container, false)
}

Solution 1

Also another reason could be that you had put setContentView below the item that caused this exception. At least it is how I fixed it on my side.

Solution 2

Sanislondra figured out that the reason why I was getting this exception because the navigation graphs id in the xml should match the id of the menu items in the bottom navigation menu xml.