如何从onCreateView方法内部设置ViewPager选项卡？

Question

好的，所以我在ViewPager中有一个Fragment，我正尝试使用数据库中的onCreateView()在Fragment的LiveData中设置ViewPager的选项卡。我期望发生的事情是改变选项卡，发生的事情是……什么都没有。我要去哪里错了？

这里是onCreateView()：

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        final View rootView = inflater.inflate(R.layout.fragment_menu, container, false);
        final MenuActivity menuAct = (MenuActivity) getActivity();
        final MenuViewModel viewModel = ViewModelProviders.of(this, new MenuViewModelFactory(menuAct.getApplication(), MenuActivity.ResID)).get(MenuViewModel.class);

        final Fragment f = this;

        viewModel.getAllMenuTitles().observe(this, new Observer<String[]>() {
            @Override
            public void onChanged(String[] strings) {
                final Spinner spinner = rootView.findViewById(R.id.spinner);
                final SubMenuViewModel subMenuViewModel = ViewModelProviders.of(f, new SubMenuViewModelFactory(menuAct.getApplication(), spinner.getSelectedItemPosition() + 1)).get(SubMenuViewModel.class);

                ArrayAdapter<String> adapter = new ArrayAdapter<String>(getContext(), R.layout.support_simple_spinner_dropdown_item, strings);
                adapter.setDropDownViewResource(R.layout.support_simple_spinner_dropdown_item);
                spinner.setAdapter(adapter);

                spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                    @Override
                    public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                        menuAct.removeAllTabs();
                        subMenuViewModel.getSubMenus().observe(f.getActivity(), new Observer<String[]>() {
                            @Override
                            public void onChanged(@Nullable String[] strings) {
                                menuAct.populateTabs(strings);
                            }
                        });
                    }

                    @Override
                    public void onNothingSelected(AdapterView<?> adapterView) {

                    }
                });
            }
        });

        return rootView;
    }

这里是removeAllTabs()：

public void removeAllTabs() {
    int cnp = mViewPager.getChildCount();
    while (cnp > 1) {
        mSectionsPagerAdapter.destroyItem(mViewPager, cnp - 1, mSectionsPagerAdapter.getItem(cnp - 1));
        mTabLayout.removeTabAt(cnp - 1);
        cnp--;
    }
    mSectionsPagerAdapter.notifyDataSetChanged();
}

这是populateTabs()：

public void populateTabs(String[] subMenus) {
    for (int i = 0; i < subMenus.length; i++) {
        mTabLayout.addTab(mTabLayout.newTab().setText(subMenus[i]),i);
        Log.d(TAG, "Added " + (subMenus[i]) + " to TabLayout");
    }

    mTabLayout.invalidate();
    mSectionsPagerAdapter.notifyDataSetChanged();
}

似乎populateTabs()根本没有运行。