Android：RecyclerView 不显示片段中的列表项

Posted 2023-04-15

【中文标题】Android：RecyclerView 不显示片段中的列表项

【英文标题】：Android: RecyclerView not showing List Items in a Fragment

【发布时间】：2018-01-31 08:25:11

【问题描述】：

谁能帮我尝试让我的 RecyclerView 出现。如果我没有在片段中实现它，它就会出现。但是，当我尝试将其实现为片段时，我在 (CarFront) 中的其他 XML 代码与 RecyclerView 分开显示。

我的日志中出现此错误： “E/RecyclerView：未连接适配器；跳过布局”

以下是我的代码，如果您需要任何其他信息或其他代码部分，请随时在下面发表评论。非常感谢。

适配器：

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewHolders> 

    private List<ItemObject> itemList;
    private Context context;

    public RecyclerViewAdapter(Context context, List<ItemObject> itemList) 
        this.itemList = itemList;
        this.context = context;
    

    @Override
    public RecyclerViewHolders onCreateViewHolder(ViewGroup parent, int viewType) 

        View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view_list, null);
        RecyclerViewHolders rcv = new RecyclerViewHolders(layoutView);
        return rcv;

    

    @Override
    public void onBindViewHolder(RecyclerViewHolders holder, int position) 
        //holder.countryName.setText(itemList.get(position).getName());
        holder.photo.setImageResource(itemList.get(position).getPhoto());


    

    @Override
    public int getItemCount() 

        Log.e("Test", "" + this.itemList.size());
        return this.itemList.size();

    

片段（欢迎）：

public class Welcome extends AppCompatActivity 

    // Declaring variables
    private ViewPager viewPager;
    private ViewPagerAdapter viewPagerAdapter;
    private LinearLayout sectionLayout;
    private TextView[] sections;
    private int[] welcome_screen;
    private Button Skip, Next;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        // Changing the window to fullscreen
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.activity_welcome);
        // Hiding the action bar to make it fullscreen
        getSupportActionBar().hide();

        // Setting the variables equal to their counter-part in the .xml
        viewPager = (ViewPager) findViewById(R.id.view_pager);
        sectionLayout = (LinearLayout) findViewById(R.id.sections_layout);
        Skip = (Button) findViewById(R.id.skip);
        Next = (Button) findViewById(R.id.next);

        // Adding the various layouts to the welcome screen
        welcome_screen = new int[]
                R.layout.activity_car_front,
                R.layout.activity_car_side;

        // adding sections
        SectionsDesign(0);

        viewPagerAdapter = new ViewPagerAdapter();
        viewPager.setAdapter(viewPagerAdapter);
        viewPager.addOnPageChangeListener(viewPagerPageChangeListener);

        //RecyclerView
        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.front_recyclerview);

    


    public  void nextclick(View v)
    

        // Checks to see if it has reached the homescreen, if so proceed
        int current = getItem(1);
        if (current < welcome_screen.length) 
            // moving to the next section
            viewPager.setCurrentItem(current);
         else 
            launchHomeScreen();
        
    

    ViewPager.OnPageChangeListener viewPagerPageChangeListener = new ViewPager.OnPageChangeListener() 

        @Override
        public void onPageSelected(int position) 
            SectionsDesign(position);

            // When it reaches the last section, show launch button
            if (position == welcome_screen.length - 1) 
                // last page. make button text to GOT IT
                Next.setText("LAUNCH");
                Skip.setVisibility(View.GONE);
             else 
                // Physical next button (blank for design)
                Next.setText("");
                Skip.setVisibility(View.VISIBLE);
            
        

        // Not using but need
        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) 

        
        @Override
        public void onPageScrollStateChanged(int arg0) 

        
    ;

    private void SectionsDesign(int currentPage) 
        // Getting how many sections there are
        sections = new TextView[welcome_screen.length];

        sectionLayout.removeAllViews();
        for (int i = 0; i < sections.length; i++) 
            sections[i] = new TextView(this);
            // Shows how many sections there are
            sections[i].setText(html.fromHtml("&#8226;"));
            // Size of the sections slider (dot)
            sections[i].setTextSize(35);
            // For other sections that isn't the one you are on
            sections[i].setTextColor(getResources().getColor(R.color.section_inactive));
            sectionLayout.addView(sections[i]);
        

        if (sections.length > 0)
            // Change colour to active
            sections[currentPage].setTextColor(getResources().getColor(R.color.section_active));
    


    private int getItem(int i) 
        return viewPager.getCurrentItem() + i;
    

    // Method for switching to the main screen
    private void launchHomeScreen() 
        startActivity(new Intent(this, Form.class));
        finish();
    

    public class ViewPagerAdapter extends PagerAdapter 
        private LayoutInflater layoutInflater;


        public ViewPagerAdapter() 

        

        @Override
        public Object instantiateItem(ViewGroup container, int position) 
            layoutInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

            View view = layoutInflater.inflate(welcome_screen[position], container, false);
            container.addView(view);

            return view;
        

        @Override
        public boolean isViewFromObject(View view, Object obj) 
            return view == obj;
        

        @Override
        // Number of sections
        public int getCount() 
            return welcome_screen.length;
        


        @Override
        public void destroyItem(ViewGroup container, int position, Object object) 
            View view = (View) object;
            container.removeView(view);
        
    

CarFront（片段中我的观点之一）：

public class CarFront extends AppCompatActivity 

    private LinearLayoutManager lLayout;
    public static ImageView fbumper;
    public static ImageView hood;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);

        //remove title/fullscreen
        //requestWindowFeature(Window.FEATURE_NO_TITLE);
        //getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                //WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.activity_car_front);
        setTitle(null);

        List<ItemObject> rowListItem = getAllItemList();
        lLayout = new LinearLayoutManager(CarFront.this);

        RecyclerView rView = (RecyclerView)findViewById(R.id.front_recyclerview);
        rView.setLayoutManager(lLayout);

        RecyclerViewAdapter rcAdapter = new RecyclerViewAdapter(CarFront.this, rowListItem);
        rView.setAdapter(rcAdapter);

        //Selected Images

        fbumper = (ImageView)findViewById(R.id.fbumperselected);
        hood = (ImageView)findViewById(R.id.hoodselected);




    

    private List<ItemObject> getAllItemList()

        List<ItemObject> allItems = new ArrayList<ItemObject>();

        allItems.add(new ItemObject("", R.drawable.hood_selected));

        //allItems.add(new ItemObject("", R.drawable.hood_card));


        return allItems;
    

    public static class ViewHolder extends RecyclerView.ViewHolder
    

        public ViewHolder(View itemView) 
            super(itemView);
        
    

车前（XML）：

<?xml version="1.0" encoding="utf-8" ?>
<LinearLayout 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_
    android:orientation="vertical"
    android:background="@color/background">

    <android.support.v7.widget.Toolbar
        android:layout_
        android:layout_
        android:background="@drawable/top_logo">

    </android.support.v7.widget.Toolbar>

    <android.support.constraint.ConstraintLayout
        android:layout_
        android:layout_>

        <ImageView
            android:id="@+id/carfront"
            android:layout_
            android:layout_
            android:scaleType="fitStart"
            app:srcCompat="@drawable/carfront"
            tools:layout_editor_absoluteY="50dp"
            tools:layout_editor_absoluteX="8dp" />

        <ImageView
            android:id="@+id/hoodselected"
            android:layout_
            android:layout_
            android:scaleType="fitStart"
            app:srcCompat="@drawable/hood_selected"
            tools:layout_editor_absoluteY="50dp"
            tools:layout_editor_absoluteX="8dp"
            android:visibility="invisible"/>


        <ImageView
            android:id="@+id/fbumperselected"
            android:layout_
            android:layout_
            android:scaleType="fitStart"
            app:srcCompat="@drawable/fbumper_selected"
            tools:layout_editor_absoluteY="0dp"
            tools:layout_editor_absoluteX="8dp"
            android:visibility="invisible"/>

    </android.support.constraint.ConstraintLayout>



        <android.support.v7.widget.RecyclerView
            android:id="@+id/front_recyclerview"
            android:layout_
            android:layout_
            android:scrollbars="none" />


</LinearLayout>

RecyclerViewHolder：

    public class RecyclerViewHolders extends RecyclerView.ViewHolder implements View.OnTouchListener

    //public TextView countryName;
    public ImageView photo;
    public ImageView fbumper;

    public RecyclerViewHolders(View itemView) 
        super(itemView);
        itemView.setOnTouchListener(this);
        photo = (ImageView)itemView.findViewById(R.id.cardview);
    

    @Override
    //make a gesture detector
    //make a nice clean graphic after they tap on repair, telling the user how it works
    //pointer = multitouch
    public boolean onTouch(View view, MotionEvent event)
    
        switch (event.getAction() & MotionEvent.ACTION_MASK)
        
            case MotionEvent.ACTION_DOWN:
                actionDown();
                break;

            case MotionEvent.ACTION_POINTER_UP:
                actionUp();
                break;
        

        return true;
    

    // Method for Down Press
    public void actionDown()
    
        switch (getAdapterPosition())
        
            case 0:

                CarFront.fbumper.setVisibility(View.VISIBLE);
                break;

            case 1:
        

    
    //Method for Up Press
    public void actionUp()
    
        switch (getAdapterPosition())
        
            case 0:

                CarFront.fbumper.setVisibility(View.INVISIBLE);
                //break;

            case 1:
        
    

（我在尝试格式化和解释我的问题时很垃圾。但是，基本上我的 RecyclerView 没有显示在我的片段中。它是为了显示 Cardview/s）

【问题讨论】：

您的 CarFront 类没有扩展 Fragment，它正在扩展 AppCompatAcvitiy。

你在哪里创建片段？我在你的代码中找不到。 Welcome 是一种受欢迎的教程吗？

好的，让我尝试帮助您修复设置中的一些项目。给我一点时间。

没关系，我只是试着重写一些东西，然后我们看看这是否有助于你走上正轨。

好的，我发布了一个关于如何构建Fragments 和ViewPager 的答案，请尝试检查一下。

【参考方案1】：

好的，首先，您的 Fragment 的结构应该更像以下内容。在您的 onCreateView 中，只需扩充布局，然后在 onViewCreated 中，您就可以绑定/填充您的信息。

我们还使用newInstance，因为这是创建新片段的标准方式。

注意，我使用的是android.support.v4.app.Fragment，而不是旧的Fragment。

public class CarFrontFragment extends Fragment 

    public ImageView bumper; // Do not use static views.
    public ImageView hood;

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

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) 
        super.onViewCreated(view, savedInstanceState);

        // Bind your views.
        RecyclerView list = (RecyclerView) view.findViewById(R.id.front_recyclerview);
        bumper = (ImageView) view.findViewById(R.id.fbumperselected);
        hood = (ImageView) view.findViewById(R.id.hoodselected);

        // Create your layout manager.
        LinearLayoutManager layout = new LinearLayoutManager(getContext());
        list.setLayoutManager(layout);

        // Fetch your items.
        List<ItemObject> rowListItem = getAllItemList();

        // Set your adapter
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(getContext(), rowListItem);
        list.setAdapter(adapter);

    

    // Creating a new Fragment through newInstance.
    public static CarFrontFragment newInstance() 
        return new CarFrontFragment();
    


    // Fetching items, passing in the View they will control.
    private List<ItemObject> getAllItemList()
        List<ItemObject> allItems = new ArrayList<ItemObject>();

        allItems.add(new ItemObject("", R.drawable.hood_selected), hood);
        allItems.add(new ItemObject("", R.drawable.bumped_selected), bumper);

        return allItems;
    

现在，对于包含这些的适配器，您需要一个FragmentStatePagerAdapter。所有这一切都会将位置绑定到您选择的Fragment。

public class PagerAdapter extends FragmentStatePagerAdapter 

    public static final int NUM_OF_PAGES = 2;
    private static final int PAGE_WELCOME = 0;
    private static final int PAGE_CAR_FRONT = 1;

    public PagerAdapter(FragmentManager fm) 
        super(fm);
    

    @Override
    public Fragment getItem(int position) 
        switch (position) 
            case PAGE_WELCOME:
                // Return a new instance of your Fragment.

            case PAGE_CAR_FRONT:
                return CarFrontFragment.newInstance();
        
        return null;
    

    @Override
    public int getCount() 
        return NUM_OF_PAGES;
    

在适配器中，我们要做的就是传递 ItemObject 所控制的View。

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewHolders> 

    private List<ItemObject> itemList;
    private Context context;

    public RecyclerViewAdapter(Context context, List<ItemObject> itemList) 
        this.itemList = itemList;
        this.context = context;
    

    @Override
    public RecyclerViewHolders onCreateViewHolder(ViewGroup parent, int viewType) 
        View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view_list, null);
        RecyclerViewHolders rcv = new RecyclerViewHolders(layoutView);
        return rcv;

    

    @Override
    public void onBindViewHolder(RecyclerViewHolders holder, int position) 
        holder.photo.setImageResource(itemList.get(position).getPhoto());
        // Telling the holder about the View.
        holder.view = itemList.get(position).getView();
    

    @Override
    public int getItemCount() 
        return itemList.size();
    

现在，在RecyclerViewHolders 中，我们将使用onTouch 切换视图的可见性。

public class RecyclerViewHolders extends RecyclerView.ViewHolder implements View.OnTouchListener 

    ImageView photo;
    public View view;

    public RecyclerViewHolders(View itemView) 
        super(itemView);
        itemView.setOnTouchListener(this);
        photo = (ImageView) itemView.findViewById(R.id.cardview);
    

    @Override
    public boolean onTouch(View view, MotionEvent event) 
        switch (event.getAction() & MotionEvent.ACTION_MASK) 
            case MotionEvent.ACTION_DOWN:
                this.view.setVisibility(View.VISIBLE);
                break;

            case MotionEvent.ACTION_POINTER_UP:
                this.view.setVisibility(View.GONE);
                break;
        

        return true;
    

【讨论】：

再次感谢您（cmets 真的很有帮助）。这看起来真的很吓人。我担心我现在可能无法像以前那样与单个卡片进行交互。我可以发布我的 RecyclerViewHolder，这样您就可以快速查看我是否还能像以前一样进行交互。

还不错，只是Fragments和一个ViewPager的基本结构而已。你想如何像以前一样与卡片互动？很难准确说出您对每张卡的用途。RecyclerViewHolder 不在您发布的代码中。

好的，你想要的只是让汽车的bumper 隐藏或显示？您可以在 Fragment 中轻松处理它。您不需要对其进行静态引用。

我已经更新了答案，Fragment 现在实现了View.OnTouchListener，您可以显示/隐藏保险杠。这样做你对 Fragment 有更多的控制，你的 Welcome 类不需要知道这些交互，Fragment 可以处理它们。

是的，只需将它们放入您的 Fragment 中，您就可以为该 Fragment 做任何您需要做的事情。