从另一个片段导航后，ViewPager在返回时不可见

Question

我有默认创建的经典底部导航，有3个TAB（FragmentOne，FragmentTwo和FragmentThree）。第一个片段（FragmentOne）具有ViewPager，其中包含两个静态内部片段（FragmentInner1和FragmentInner2）。

当应用程序启动时，evrything很好，所以在FragmentOne中我们可以看到FragmentInner1并可以导航到FragmentInner2。

但是在从FragmentTwo导航到FragmentOne后，FragmentInner1不可见。这是一个问题。

我想我们应该以某种方式再创造它？我从这里https://developer.android.com/guide/components/fragments.html和https://developer.android.com/training/implementing-navigation/lateral.html#PagerTitleStrip调查手册，但它没有帮助，我的代码看起来一样。

请帮忙。谢谢！

FragmentOne

public class FragmentOne extends Fragment {

    //This is our viewPager
    private ViewPager viewPager;

    //Fragments
    FragmentInner1 fragmentInner1;
    FragmentInner2 fragmentInner2;

    ViewPagerAdapter adapter;

    private View view;

    public FragmentOne() {
    }

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

         view = inflater.inflate(R.layout.fragment_fragment_one, container, false);

        //Initializing viewPager
        viewPager = (ViewPager) view.findViewById(R.id.viewpager);

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

        setupViewPager(viewPager);

        return view;
    }

    private void setupViewPager(ViewPager viewPager) {
        adapter  = new ViewPagerAdapter(getActivity().getSupportFragmentManager());
        fragmentInner1=new FragmentInner1();
        fragmentInner2=new FragmentInner2();
        adapter.addFragment(fragmentInner1);
        adapter.addFragment(fragmentInner2);
        viewPager.setAdapter(adapter);
    }

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

    @Override
    public void onResume() {
        super.onResume();

    }

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

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

ViewPagerAdapter

public class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();

    public ViewPagerAdapter(FragmentManager manager) {
        super(manager);
    }
    @Override
    public Fragment getItem(int position) {
        Fragment fragment = mFragmentList.get(position);
        return fragment;
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFragment(Fragment fragment) {
        mFragmentList.add(fragment);
    }
}

FragmentInner1

public class FragmentInner1 extends Fragment {

    public static FragmentInner1 newInstance( ) {
        FragmentInner1 fragment = new FragmentInner1();
        return fragment;
    }

    public FragmentInner1() {
    }    

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {     
        return inflater.inflate(R.layout.fragment_fragment_inner1, container, false);
    }

}

Answer 1

您必须使用getChildFragmentManager() For Viewpager来调整Popback功能。

adapter  = new ViewPagerAdapter(getChildFragmentManager());

这是因为Viewpager有多个片段，其中Viewpager本身或由另一个片段持有。因此，要调用和使用子片段。

You Can Refer this Documentation on ChildFragmentManager()