Android 如何根据列表是否为空在主活动中显示片段？

我正在为即将到来的生日开发一款Android应用程序。我有一种方法，可以检查SQLite数据库中的日期，看两天后是否有即将到来的生日，然后加载到列表中。还有两个片段：main片段和BirthdayFragment。在启动应用程序时，我希望仅当列表包含某些内容时显示BirthdayFragment，如果没有，则应显示MainFragment。但当我使用下面的代码启动应用程序时，它显示了一个空的活动。当列表为空和不为空时，我尝试了这个方法

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

    //check for upcoming birthday here...
    //if we have birthday, display Birthday Fragment
    DatabaseOperations dbo = new DatabaseOperations(getApplicationContext());
    List<Student> studentList = dbo.getAllStudentsToList();
    if (studentList.isEmpty())
        //if we don't have any birthday, display main fragment
        if (savedInstanceState == null) {
            MainFragment fragment = new MainFragment();
            replaceFragment(fragment);
        }
    else {//if we have any birthday, display birthday fragment
        BirthdayFragment birthdayFragment = new BirthdayFragment();
        replaceFragment(birthdayFragment);
    }
}

下面是替换片段的方法

public void replaceFragment(Fragment fragment){
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    fragmentTransaction.replace(R.id.fragment_container, fragment);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

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我需要你的帮助

尽量不要将其放入savedInstanceState中，而是使用getSupportFragmentManager而不是getFragmentManager@ChataBirthdayFragment是否在后台线程上正确处理sql请求？在删除savedInstanceState If块后，它工作正常。非常感谢。@Lino它不在后台线程中

public void replaceFragment(Fragment fragment){
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    fragmentTransaction.replace(R.id.fragment_container, fragment);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}