Android Studio -在片段之间切换时底部导航崩溃

public class MainActivity extends AppCompatActivity {

    private BottomNavigationView bottomNavigationView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        bottomNavigationView = findViewById(R.id.bottom_navigation);
        bottomNavigationView.setOnNavigationItemSelectedListener(navListener);

        // 设置默认显示的Fragment
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, new HomeFragment()).commit();
    }

    private BottomNavigationView.OnNavigationItemSelectedListener navListener =
            new BottomNavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                    Fragment selectedFragment = null;
                    switch (item.getItemId()) {
                        case R.id.navigation_home:
                            selectedFragment = new HomeFragment();
                            break;
                        case R.id.navigation_dashboard:
                            selectedFragment = new DashboardFragment();
                            break;
                        case R.id.navigation_notifications:
                            selectedFragment = new NotificationsFragment();
                            break;
                    }
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, selectedFragment).commit();
                    return true;
                }
            };
}