选项卡布局不显示片段

Posted 2023-04-18

【中文标题】选项卡布局不显示片段

【英文标题】：Tab Layout not showing fragments

【发布时间】：2021-11-20 19:34:53

【问题描述】：

我有一个名为“通知片段”的片段，我想在其中使用选项卡布局显示另一个名为“观看片段”的片段。当我运行应用程序时，选项卡布局栏可见，但片段不可见。

我的 Fragment 将在其中显示其他 Fragment（通知 Fragment）

public class NotificationsFragment extends Fragment


    GridView listv;
    FragmentAdapter fragmentAdapter;

    private NotificationsViewModel notificationsViewModel;
    private FragmentNotificationsBinding binding;

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) 
        notificationsViewModel =
                new ViewModelProvider(this).get(NotificationsViewModel.class);

        binding = FragmentNotificationsBinding.inflate(inflater, container, false);
        View root = binding.getRoot();

        TabLayout tabLayout = root.findViewById(R.id.tabLayout);
        ViewPager vp = root.findViewById(R.id.vp2);

        fragmentAdapter = new FragmentAdapter(getChildFragmentManager() , tabLayout.getTabCount());
        vp.setAdapter(fragmentAdapter);

        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() 
                @Override
                public void onTabSelected(TabLayout.Tab tab) 
                    vp.setCurrentItem(tab.getPosition());

                    if(tab.getPosition() == 0 || tab.getPosition() == 1 || tab.getPosition() == 2)
                            fragmentAdapter.notifyDataSetChanged();
                    

                    @Override
                    public void onTabUnselected(TabLayout.Tab tab) 

                    

                    @Override
                    public void onTabReselected(TabLayout.Tab tab) 

                    
                );

               vp.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

    return  root; 

我的第一个片段（观看片段）

public class WatchingFragment extends Fragment 

    ArrayList<String> list = new ArrayList<String>();
    GridView gridv1;

    private WatchingViewModel mViewModel;

    public static WatchingFragment newInstance() 
        return new WatchingFragment();
    

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

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

        gridv1 = view.findViewById(R.id.gridv1);


        Intent intent = getActivity().getIntent();
        String animename = intent.getStringExtra("nameanime");
        list.add(animename);


        loadData2();
        saveData2();

        ListNewAdapter adapter = new ListNewAdapter(getContext(), R.layout.watch_list, list);
       gridv1.setAdapter(adapter);
        gridv1.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() 
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) 
                list.remove(position);
                adapter.notifyDataSetChanged();
                saveData2();
                return true;
            
        );

    return view;
    

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) 
        super.onActivityCreated(savedInstanceState);
        mViewModel = new ViewModelProvider(this).get(WatchingViewModel.class);
        // TODO: Use the ViewModel
    

    private void saveData2() 
        SharedPreferences sp = getActivity().getSharedPreferences("shared preferences", MODE_PRIVATE);
        SharedPreferences.Editor ed = sp.edit();
        Gson gson = new Gson();
        String json = gson.toJson(list);
        ed.putString("anime list", json);
        ed.apply();
    

    private void loadData2() 
        SharedPreferences sp = getActivity().getSharedPreferences("shared preferences", MODE_PRIVATE);
        Gson gson = new Gson();
        String json = sp.getString("anime list", "");
        Type type = new TypeToken<ArrayList<String>>() .getType();
        list = gson.fromJson(json , type);

        if (list == null) 
            list = new ArrayList<String>();
        

    

我的视图寻呼机适配器

public class FragmentAdapter extends FragmentPagerAdapter 
int tabcount;
    public FragmentAdapter(@NonNull @NotNull FragmentManager fm, int behavior) 
        super(fm, behavior);
        tabcount = behavior;
    

    @NonNull
    @NotNull
    @Override
    public Fragment getItem(int position) 
        switch (position)
            case 0: return new WatchingFragment();
            case 1: return new CompletedFragment();
            case 2: return new WantToWatchFragment();
            default: return null;
        
    

    @Override
    public int getCount() 
        return 0;
    

通知片段布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_
    android:layout_
    tools:context=".ui.notifications.NotificationsFragment">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        android:layout_
        android:layout_
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <com.google.android.material.tabs.TabItem
            android:layout_
            android:layout_
            android:text="Watching" />

        <com.google.android.material.tabs.TabItem
            android:layout_
            android:layout_
            android:text="Completed" />

        <com.google.android.material.tabs.TabItem
            android:layout_
            android:layout_
            android:text="Want To Watch" />
    </com.google.android.material.tabs.TabLayout>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/vp2"
        android:name="com.example.animeguide.ui.notifications.NotificationsFragment"
        android:layout_
        android:layout_
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/tabLayout" />

</androidx.constraintlayout.widget.ConstraintLayout>

查看片段布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_
    android:layout_
    android:orientation="vertical"
    tools:context=".ui.notifications.FragmentsInsideList.watching.WatchingFragment">

    <TextView
        android:id="@+id/textView4"
        android:layout_
        android:layout_
        android:text="hello world"
        android:textSize="34sp" />

    <GridView
        android:id="@+id/gridv1"
        android:layout_
        android:layout_
        android:numColumns="2" />

</LinearLayout>

【参考方案1】：

为了让 Adapter 知道它有多少页，你需要重写 getCount 方法。您确实覆盖了它，但使用 0 作为页数，因此没有页。

在您的 FragmentAdapter 类中，尝试更改：

@Override
public int getCount() 
    return 0;

到这里：

@Override
public int getCount() 
    return tabcount;

【讨论】：

知道了。谢谢。