android - 当我移动到相邻页面之外时，带有 TabLayout 的 ViewPager 不显示来自 recyclerview 的列表

Question

这就是我的应用正在做的事情。我在 FragmentPagerAdapter 中使用 TabLayout 有四个选项卡:A、B、C 和 D。我只在 B 处显示数据。该应用程序在选项卡 B 启动。我可以从选项卡 B 向左翻页到 A，然后返回到选项卡 B，数据仍然显示正常。然后我可以从选项卡 B 向右翻页到选项卡 C，然后返回到选项卡 B，数据也可以正常显示。但是一旦我翻页到选项卡 D，然后翻页回到选项卡 B，页面就完全变空了。我显示的 RecyclerView 列表不再显示任何内容。我刚开始使用 FragmentPagerAdapter 和 TabLayout(以及一般的 Android 编程)，所以如果我的代码有问题或其他问题，我深表歉意。

顺便说一句，我的 ViewPager 位于 Activity 内部(尽管各个页面都是 Fragment，希望不会造成混淆)所以我无法使用 getChildFragmentManager() 很多答案都在暗示(除非我做错了)。我在这里阅读了 viewpager 上的许多答案，但似乎他们遇到的问题与我不同。这是我的代码:

主要 Activity :

public class MainActivity extends AppCompatActivity
{
    private Toolbar mToolbar;
    private ViewPager mViewPager;
    private TabLayout mTabLayout;

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

        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        mViewPager = (ViewPager) findViewById(R.id.main_activity_view_pager);
        mTabLayout = (TabLayout) findViewById(R.id.main_activity_tab_layout);

        setSupportActionBar(mToolbar);
        assert getSupportActionBar() != null;
        getSupportActionBar().setDisplayShowTitleEnabled(false);

        NavDrawerFragment navDrawerFrag = (NavDrawerFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_nav_drawer);
        navDrawerFrag.setUp((DrawerLayout)findViewById(R.id.nav_drawer), mToolbar);

        setupViewPagerAdapter(mViewPager);
        mTabLayout.setupWithViewPager(mViewPager);

        mTabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener()
        {
            @Override
            public void onTabSelected(TabLayout.Tab tab)
            {
                mViewPager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab)
            {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab)
            {

            }
        });

    private void setupViewPagerAdapter(ViewPager viewPager)
    {
        MainPagerAdapter pagerAdapter = new MainPagerAdapter(getSupportFragmentManager());

        //order is very important here; they correspond to the tab position from left to right
        pagerAdapter.addFragment(MyGamesFragment.newInstance(), "My Games");
        pagerAdapter.addFragment(AllGamesFragment.newInstance(), "All Games");
        pagerAdapter.addFragment(AllPlacesFragment.newInstance(), "All Places");
        pagerAdapter.addFragment(MyPlacesFragment.newInstance(), "My Places");

        viewPager.setAdapter(pagerAdapter);
        viewPager.setCurrentItem(1);
}

MainPagerAdapter(FragmentPagerAdapter 类):

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

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

    @Override
    public Fragment getItem(int position)
    {
        return mFragmentList.get(position);
    }

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

    @Override
    public CharSequence getPageTitle(int position)
    {
        return mFragmentTitleList.get(position);
    }

    public void addFragment(Fragment fragment, String title)
    {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }
}

我的 fragment (这代表我上面解释中的“选项卡 B”):

public class AllGamesFragment extends Fragment
{
    private static final String ARG_ALLGAMES_FRAG_ID = "all_games_frag_id";
    RecyclerView mAllGamesRecyclerView;
    GameAdapter mGameAdapter;

    public static AllGamesFragment newInstance()
    {
        return new AllGamesFragment();
    }

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

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.inflate(R.layout.all_games_recycler_view, container, false);
        mAllGamesRecyclerView = (RecyclerView) view.findViewById(R.id.all_games_recycler_view);
        mAllGamesRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        updateList();

        return view;
    }

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

    private void updateList()
    {
        if(mGameAdapter == null)
        {
            mGameAdapter = new GameAdapter();
            mAllGamesRecyclerView.setAdapter(mGameAdapter);
        }
    }

    private class GameHolder extends RecyclerView.ViewHolder implements View.OnClickListener
    {
        private TextView mTeamOne, mTeamTwo, mGameStartTime;
        private ImageView mTeamOneLogo, mTeamTwoLogo;

        public GameHolder(View itemView)
        {
            super(itemView);
            itemView.setOnClickListener(this);

            mTeamOne = (TextView) itemView.findViewById(R.id.team_one_name);
            mTeamTwo = (TextView) itemView.findViewById(R.id.team_two_name);
            mTeamOneLogo = (ImageView) itemView.findViewById(R.id.team_one_logo);
            mTeamTwoLogo = (ImageView) itemView.findViewById(R.id.team_two_logo);
            mGameStartTime = (TextView) itemView.findViewById(R.id.game_time);
        }

        @Override
        public void onClick(View v)
        {

        }
    }

    private class GameAdapter extends RecyclerView.Adapter<GameHolder>
    {
        @Override
        public GameHolder onCreateViewHolder(ViewGroup parent, int viewType)
        {
            LayoutInflater inflater = LayoutInflater.from(getActivity());
            View view = inflater.inflate(R.layout.list_game_item, parent, false);
            return new GameHolder(view);
        }

        @Override
        public void onBindViewHolder(GameHolder holder, int position)
        {

        }

        @Override
        public int getItemCount()
        {
            return 10;
        }
    }

如您所见，我还没有使用实际数据，我只是想让 UI 正常工作。

Answer 1

更改代码

if(mGameAdapter == null)
        {
            mGameAdapter = new GameAdapter();
            mAllGamesRecyclerView.setAdapter(mGameAdapter);
        }

到

    mGameAdapter = new GameAdapter();
    mAllGamesRecyclerView.setAdapter(mGameAdapter);