java - 选项卡 fragment 不显示

Question

我正在尝试在 fragment 中添加选项卡(用于底部导航栏)。但是，当我运行该应用程序时，选项卡根本不显示。下面是结果的图像:

IMAGE

• Home.java -> 应显示 2 个选项卡的 fragment ，其中包括 BlankFragment.java

• CategoryAdapater.java -> 设置要在每个选项卡中显示的选项卡名称和 fragment

• BlankFragment.java -> 每个选项卡上显示的空 fragment

我怎样才能让它工作？

<小时/>

Home.java(应显示选项卡的 fragment )

public class Home extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View rootView = inflater.inflate(R.layout.fragment_home, container, false);

    ViewPager viewPager = rootView.findViewById(R.id.viewpager);
    CategoryAdapter adapter = new CategoryAdapter(getChildFragmentManager());
    viewPager.setAdapter(adapter);
    TabLayout tabLayout = rootView.findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);

    return rootView;
}

public Home() {}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
}

@Override
public void onDetach() {
    super.onDetach();
}

<小时/>

类别Adapater.java

public class CategoryAdapter extends FragmentPagerAdapter {

public CategoryAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int position) {
    if (position == 0) {
        return new BlankFragment();
    } else {
        return new BlankFragment();
    }
}

@Override
public int getCount() {
    return 2;
}

@Override
public CharSequence getPageTitle(int position) {
    if (position == 0) {
        return "Devices";
    } else {
        return "Numbers";
        }
    }
}

<小时/>

BlankFragment.java

public class BlankFragment extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View rootView = inflater.inflate(R.layout.fragment_blank, container, false);

    return rootView;
}

public BlankFragment() {}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
}

@Override
public void onDetach() {
    super.onDetach();
   }
}

Answer 1

适配器addFragment丢失

    ViewPager viewPager = rootView.findViewById(R.id.viewpager);
    CategoryAdapter adapter = new CategoryAdapter(getChildFragmentManager());
    BlankFragment frag= new BlankFragment ();
    adapter.addFragment(frag);
    viewPager.setAdapter(adapter);
    TabLayout tabLayout = rootView.findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);