小编Ars*_*a13的帖子

我的MainActivity.java中有3个片段的底部导航。我想将片段之一设置为默认值，以在应用程序启动时自动打开。我怎样才能做到这一点？这是我的主要Activity.java：

public class MainActivity extends AppCompatActivity {
private static final String TAG = MainActivity.class.getSimpleName();
private BottomNavigationView bottomNavigation;
private Fragment fragment;
private android.support.v4.app.FragmentManager fragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    bottomNavigation = (BottomNavigationView)findViewById(R.id.bottom_navigation);
    bottomNavigation.inflateMenu(R.menu.bottom_menu);
    fragmentManager = getSupportFragmentManager();



    bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            Fragment selectedFragment = null;
            int id = item.getItemId();
            switch (id){
                case R.id.intros:
                    fragment = new IntrosFragment();
                    break;
                case R.id.menus:
                    fragment = new MenusFragment();
                    break;
                case R.id.infos:
                    fragment = new InfosFragment();
                    break;
            } …