Starting a new activity on navigation drawer item click

Instead of

NavigationUI.setupWithNavController(navigationView, navController);

Do this

navigationView.setNavigationItemSelectedListener(new 
    NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) { 
            Toast.makeText(MainActivity.this, "clicked", Toast.LENGTH_SHORT).show();
            return false;
        }
    }
);

For each case statement you just need to specify which Activity you want to start via an Intent.

Say for example you want to start the Playboard activity when navigation_item_1 is selected.

You would add this code to that particular case.

case R.id.navigation_item_1:
    Intent i = new Intent(MainActivity.this, Playboard.class);
    startActivity(i);
    break;